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Appendix:Dictionary of Mining, Mineral, and Related Terms/P/4

pit
 * a. Depression produced in a metal surface by nonuniform electrodeposition or by corrsion.

b. Excavation to hold quantities of water and drilling fluids. c. So. Wales. Long, open-air fire for converting coal into coke for blast-furnace purposes. d. A mine, quarry, or excavation worked by the open-cut method to obtain material of value. e. The shaft of a mine; a shaft mine; a trial pit. f. The underground portion of a colliery, including all workings. Used in many combinations, as pit car, pit clothes, etc. g. In hydraulic mining, the excavation in which piping is carried forward. h. Commonly, a coal mine, but not usually called so by workers, except in reference to surface mining where the workings may be known as a strip pit. i. See: abyss.

pit ash
 * Ash in coal derived from the dirt bands, adjoining shales or cleat minerals.

pit bank
 * a. Eng. The raised ground or platforms upon which the coal is sorted and screened at the surface. See also: heapstead; pit brow; pithead; pit hill.

b. Scot. The surface of the ground at the mouth of a pit, or shaft.

pit bar
 * One of the wooden props bracing the sides of a pit.

pit boss
 * A mine foreman who is in direct charge of workers in a specific portion of a pit or mine. Also called shift boss. See also: pit foreman.

pit bottom
 * The bottom of a shaft and all the equipment and roadways around it. See also: loop-type pit bottom.

pit brow
 * The pithead, and in particular, the mouth of the shaft. The edge or brow of a pit. See also: brow.

pit cage
 * The structure used in mine shafts for transport purposes. See also: cage.

pit-car loader
 * A short, electrically powered, lightweight elevating conveyor designed for use in working places, to facilitate the loading of large cars or to aid in shoveling long distances. The loader shovels into the hopper end and the conveyor carries the coal to the car.

pit-car-loader operator
 * In bituminous coal mining, a person who operates a machine to load coal in mine (pit) cars.

pit-car repairer
 * See: mine-car repairman.

pitch
 * a. The angle between the horizontal and any linear feature, such as an ore shoot or lineation, measured in the plane containing the linear feature. See also: rake.

b. The angle between the horizontal and an axial line passing through the highest or lowest points of a given stratum in an anticline or syncline. c. Loosely, the grade, rise, or incline of a seam or bed. d. A vein-form deposit that follows dipping joint planes. This usage is confined largely to the Upper Mississippi Valley lead-zinc deposits. e. The slope of a roof, in inches (or centimeters), of vertical rise per horizontal foot (or meter). f. The distance between tooth centers, as in a gear wheel, or the number of teeth per unit of diameter. See also: pitch line. g. The grade of an incline or the rise of a coal seam. h. The solid or semisolid residue from the partial evaporation of tar. Strictly, pitch is a bitumen with extraneous matter, such as free carbon, residual coke, etc. i. The angular inclination of an ore shoot with respect to the surface, measured in the direction of the strike. j. Of a lode, angle of deviation from the vertical taken by a section of ore having some special characteristic, such as enhanced value. k. The angle that a directional feature, for example, slickensides, in a plane makes with a horizontal line within the plane. l. In dredging, the distance between the center of any pin and that of the pin in the next adjacent bucket. m. See: dip. n. The slope of a surface or tooth relative to its direction of movement. o. In a roller or silent chain, the space between pins, measured center to center. p. The amount of advance of a single-thread screw in one turn, expressed in lineal distance along or parallel to the axis, or in turns per unit of length. q. The distance between corresponding points on adjacent projections produced on work by a cutting tool.

pitch arm
 * One of the rods, usually adjustable, which determine the digging angle of a blade or bucket.

pitchblende
 * The massive variety of uraninite, UO (sub (2+x)) ; radioactive; black to dark brown; the most important ore of uranium; occurs widely in hydrothermal veins and the disseminated uranium-vanadium deposits of the Colorado Plateau type. Syn: pitch ore. CF: uraninite.

pitch circle
 * The circle passing through the chain joint centers when the chain is wrapped on the sprocket.

pitch diameter
 * The diameter of a circle that passes through the points of average contact between the teeth of two gears running in mesh, or between the teeth of a sprocket and the roller of its companion chain, or between a male and a female thread that are engaged.

pitcher
 * One who picks over dumps for pieces of ore.

pitches and flats
 * See: flats and pitches.

pitching bar
 * A kind of pick used, esp. by miners, in beginning a hole.

pitching chisel
 * A chisel used for making an edge on the face of a stone. Also called pitching tool.

pitching seam
 * A highly inclined seam. In coal mining, called edge coal.

pitch length
 * The length of an ore shoot in its greatest dimension.

pitch line
 * a. The line on which the pitch of gear teeth is measured; an ideal line, in a toothed gear or rack, bearing such a relation to a corresponding line in another gear with which the former works that the two lines will have a common velocity, as in rolling contact. See also: pitch.

b. The line along which the pitch of a rack is marked out, corresponding to the pitch circle of a spur wheel.

pitch off
 * A quarry worker's term for trimming an edge of a block of stone with a hammer and set.

pitch ore
 * See: pitchblende; pitchy copper ore.

pitchstone
 * A dark, resinous volcanic glass.

pitchwork
 * In coal mining, work done on shares.

pitch working
 * Mine working in a steeply inclined seam.

pitchy
 * adj. Resembling the appearance or properties of pitch.

pitchy copper ore
 * a. A dark, pitchlike oxide of copper. Syn: pitch ore.

b. A mixture of chrysocolla and limonite.

pitchy iron ore
 * a. An old syn. for pitticite. See: pitticite.

b. See: triplite.

pit efficiency
 * In order to allow for the friction of the skips on the guides and between the air and the skips in the shaft and for other small losses, it is usual to divide the total static torque at any point of the wind by 0.9 for a new shaft with rope guides, or 0.85 for an old shaft with rigid guides. This factor is generally referred to as pit efficiency.

pit eye
 * Bottom of a pit shaft from which the sky is visible.

pit-eye pillar
 * A barrier of coal left around a shaft to protect it from caving.

pit foreman
 * In bituminous coal mining, a foreman who is in immediate charge of all mining operations in a strip mine. See also: pit boss.

pit frame
 * a. The framework carrying the pit pulley. See also: headframe.

b. The framework in a coal mine shaft.

pit guide
 * An iron column that guides the cage in a mine shaft.

pit hand
 * In the iron and steel industry, a general term applied to workers who perform varied duties around the processing furnaces.

pithead
 * a. Landing stage at the top of a shaft.

b. The top of a mine shaft including the buildings, roads, tracks, plant, and machines around it. See also: pit brow.

pithead output
 * The total tonnage of raw coal produced at a colliery, as distinct from saleable output. It is the tonnage of coal as weighed before it enters the coal-preparation plant. See also: run-of-mine.

pit hill
 * Eng. See: pit bank.

pit lamp
 * An open lamp worn on a miner's cap, as distinguished from a safety lamp.

pit limit
 * Either the vertical or lateral extent to which the mining of a mineral deposit by open pitting may be economically carried. The cost of removing overburden or waste material versus the minable value of the ore so exposed is usually the factor controlling the limits of a pit.

pitman
 * a. The worker who regularly examines the condition of mine infrastructure.

b. A connecting rod, such as in the Blake type of jaw crusher; the vertical member linking the eccentric shaft with the toggles between the frame and the lower end of the movable jaw.

pitman arm
 * An arm having a limited movement around a pivot.

pitmen
 * Workers employed in shaft sinking or shaft inspection and repair.

pit mining
 * Surface mining in which the material mined is removed from below the surrounding land surface.

pitotmeter
 * An instrument that consists essentially of two pitot tubes one of which is turned upstream and the other downstream and that is used to record autographically the velocity of a flowing liquid or gas.

Pitot-static tube
 * When the Pitot tube and static tube are combined, they form the Pitot-static tube, and as such they can be used as an anemometer. The tubes are usually arranged concentrically. When they are connected to the opposite sides of a manometer, the dynamic or velocity pressure will be measured directly.

Pitot tube
 * Consists of two concentric tubes bent in an L shape. In operation, the instrument is pointed in the direction of air flow: the inner tube, open at the end directed upstream, measures total head, and the outer tube, perforated with small openings transverse to the air flow, records static head. Each tube is connected to a leg of a manometer, when reading velocity head.

pit pony
 * A pony used for packing or haulage in a mine.

pit prop
 * a. A piece of timber used as a temporary support for a mine roof.

b. Length of timber used as a roof support in longwall mining. Modern variants include expandable steel props which can be hydraulically or mechanically lengthened; used in stratified deposits.

pit quarry
 * An openpit quarry sunk below ground level. Access is gained by stairs, ladders, or mechanical hoists, and material is conveyed from the quarry by inclined tracks, trucks, derricks, or cableway hoists. These pits may reach depths of several hundred feet. A drainage scheme will in most cases be necessary, as the pit will form a natural sump for both surface and subsoil water. This type of quarry is often used for gravel or soft rock that can be extracted by some form of digging. See also: hillside quarry.

pit room
 * a. The number of working places, or the length of a longwall face, available in a mine for coal production.

b. The extent of the opening in a mine; pit space.

pit rope
 * Eng. Winding rope; a hoisting rope.

pit sampling
 * a. Use of small untimbered pits to gain access to shallow alluvial deposits or ore dumps for purpose of testing or valuation.

b. Sampling shallow deposits by means of trial pits, usually about 2 to 3 ft (0.6 to 0.9 m) in diameter. In reasonably dry ground, depths of 50 ft (15.2 m) or more may be reached. Pit sampling is often used to assist site investigations as it provides the maximum of information regarding the nature of deposits and bedrock. See also: trial pit.

pit sand
 * a. Sand usually composed of grains that are relatively angular; it often contains clay and organic matter. When washed and screened it is a good sand for general purposes.

b. Sand from a pit, as distinct from river or sea sand.

pit shale
 * The name given to the shale from a drift opened in the side of the ravine at a level 62 ft (18.9 m) below that of the Pittsburgh coal seam.

pit slope
 * The angle at which the wall of an open pit or cut stands as measured along an imaginary plane extended along the crests of the berms or from the slope crest to its toe.

pittasphalt
 * An old name give to viscid bitumen. Syn: maltha. See also: mineral tar.

pitticite
 * The mineral amorphous, hydrous, ferric arsenate sulfate. It is brown to yellow and red; earthy; occurs as crusts and botryoidal layers; a common oxidation product of arsenical ores. Also spelled pittizite. Syn: pitchy iron ore.

pitting
 * a. The act of digging or sinking a pit.

b. Testing an alluvial deposit by the systematic sinking of small shafts, the material recovered being subsequently tested. The practice is confined to shallow depths; i.e., down to about 50 ft (15.2 m) in fairly dry soft ground.

Pittsburgh bed
 * The Pittsburgh coal which outcrops prominently in the vicinity of Pittsburgh and extends under a large area of western Pennsylvania, northern West Virginia, northwestern Maryland, and eastern Ohio. It belongs in the Carboniferous system, Pennsylvanian series, at the base of the Monongahela formation.

pit water
 * Water from the underground workings of a mine.

pit wood
 * The various kinds of timber used at a mine, mainly as supports.

pitwork
 * Cornish pumps and other engineering appliances in and near a mine shaft.

pivot
 * A nonrotating axle or hinge pin.

pivoted-bucket carrier
 * The highest type of combined elevator and conveyor. It consists of two long-pitch roller chains joined by crossbars on which are hung the buckets in such a way that they can be completely turned over.

pivoted-bucket conveyor
 * A type of conveyor using pivoted buckets attached between two endless chains that operate in suitable guides or casing in horizontal, vertical, inclined or a combination of these paths over drive-corner and takeup terminals. The buckets remain in the carrying position until they are tipped or inverted to discharge. Syn: bucket elevator.

pivot shaft
 * A tractor dead axle, or any fixed shaft that acts as a hinge pin.

pivot tube
 * A hollow hinge pin.

place
 * a. See: in situ.

b. The part of a mine in which a miner works by contract is known as his "place" or "working place." c. A point at which the cutting of coal is being carried on.

placer
 * A deposit of sand or gravel that contains particles of gold, ilmenite, gemstones, or other heavy minerals of value. The common types are stream gravels and beach sands. See also: alluvial deposit; beach placer.

placer claim
 * a. A mining claim located upon gravel or ground whose mineral contents are extracted by the use of water, by sluicing, hydraulicking, etc. The unit claim is 1,320 ft (super 2) (122.6 m (super 2) ) and contains 10 acres (4.1 ha). See also: mining claim.

b. Ground with defined boundaries that contains mineral in the earth, sand, or gravel; ground that includes valuable deposits not fixed in the rock. See also: claim; lode claim. c. The maximum size of a placer claim is 20 acres (8.1 ha). Association claims of two or more persons may be located up to an area of 160 acres (64.8 ha) for eight persons. Placer claims must have a discovery. They should be staked, a location notice posted, and recorded in the same manner as for lode claims, stating the mineral for which the location in made.

placer digging
 * a. The action of mining by placer methods.

b. A place at which placer mining is or may be carried on.

placer gold
 * Gold occurring in more or less coarse grains or flakes and obtainable by washing the sand, gravel, etc., in which it is found. Also called alluvial gold. See also: stream gold. Syn: wash gold.

placer ground
 * Ground where placer mining can be done; i.e., where valuable minerals can be obtained by digging up the earth and washing it for the valued mineral.

placer location
 * A location of a tract of land for mineral-bearing or other valuable deposits upon or within it that are not found within lodes or veins in rock in place; a claim of a tract of land for the sake of the loose deposits on or near its surface.

placer mine
 * a. A deposit of sand, gravel, or talus from which some valuable mineral is extracted.

b. See: placer mining.

placer mining
 * a. The extraction of heavy mineral from a placer deposit by concentration in running water. It includes ground sluicing, panning, shoveling gravel into a sluice, scraping by power scraper and excavation by dragline, dredge or other mechanized equipment.

b. Extracting the gold or other mineral from placers, wherever situated--in dry channels and in channels temporarily filled with water. The mineral may be found in deep channels, in navigable streams, or in estuaries or creeks and rivers where the sea ebbs and flows. c. That form of mining in which the surficial detritus is washed for gold or other valuable minerals. When water under pressure is employed to break down the gravel, the term hydraulic mining is generally employed. There are deposits of detrital material containing gold which lie too deep to be profitably extracted by surface mining, and which must be worked by drifting beneath the overlying barren material. The term "drift mining" is applied to the operations necessary to extract such auriferous material. See also: dredge. Syn: placer mine. d. The extraction and concentration of heavy metals or minerals from placer deposits by various methods, generally using running water. CF: alluvial mining; hydraulic mining; drift mining.

placodine
 * See: maucherite.

plaffeiite
 * A fossil resin found in Switzerland.

plagihedral
 * See: plagiohedral.

plagioclase
 * a. Any of a group of feldspars containing a mixture of sodium and calcium feldspars, distinguished by their extinction angles; crystal; triclinic; Mohs hardness, 6; and sp gr, 2.6 to 2.7.

b. A series of triclinic feldspars of general formula: (Na,Ca)Al(Si,Al)Si (sub 2) O (sub 6) ; at high temperatures it forms a complete crystal solution series from albite, NaAlSi (sub 3) O (sub 8), to anorthite, An, CaAl (sub 2) Si (sub 2) O (sub 8) ; the series is arbitrarily subdivided and named according to increasing mole fraction of the An component: albite (An 0% to 10%), oligoclase (An 10% to 30%), andesine (An 30% to 50%), labradorite (An 50% to 70%), bytownite (An 70% to 90%), and anorthite (An 90% to 100%). The Al:Si ratio ranges with increasing An content from 1:3 to 1:1. Plagioclase feldspars are common rock-forming minerals, have characteristic polysynthetic twinning, and commonly display zoning. The term was originally applied to all feldspars having an oblique angle between the two main cleavages. CF: alkali feldspar; orthoclase. Syn: sodium-calcium feldspar.

plagioclase rhyolite
 * A porphyritic extrusive rock with phenocrysts of plagioclase and quartz in a groundmass of orthoclase and quartz. Also called plagioliparite. Syn: dellenite.

plagioclastic
 * Having the cleavage of plagioclase; breaking obliquely.

plagiohedral
 * Having an oblique spiral arrangement of faces; specif., being a group of the isometric system characterized by 13 axes of symmetry but no center or planes. Also spelled plagihedral.

plagionite
 * A monoclinic mineral, Pb (sub 5) Sb (sub 8) S (sub 17) ; metallic black to lead-gray; forms stubby tablets; an uncommon associate of other lead sulfosalts in hydrothermal veins.

plain
 * a. An extent of level, or nearly level, land; a region not noticeably diversified with mountains, hills, or valleys.

b. A flat, gently sloping or nearly level region of the sea floor. c. Archaic. Relatively free of gaseous inclusions.

plain clinometer
 * A clinometer having only its upper end threaded to fit drill rods. Also called end clinometer. See also: clinometer. CF: line clinometer; wedge clinometer.

plain concrete
 * Concrete with no reinforcement.

plain detonator
 * A detonator for use with a safety fuse. It consists of an aluminum tube closed at one end and partly filled with a sensitive initiating explosive. The tube is only partially filled because a plain detonator is always used in conjunction with a safety fuse, and the empty space enables the fuse to be inserted into the tube until it comes into contact with the detonating composition. The safety fuse is then secured in position by indenting the detonator tube, this process being known as crimping. The combination of safety fuse and plain detonator is called a capped fuse.

plain pilot
 * A pilot in the surface of which no cutting points, such as diamonds or slugs, are inset. See also: pilot.

plaiting
 * A texture seen in some schists that results from the intersection of relict bedding planes with well developed cleavage planes.

plan
 * a. A map showing features--such as mine workings, geological structures, and outside improvements--on a horizontal plane. See also: colliery plan.

b. A scheme or project for mine development. See also: planning. c. The system on which a colliery is worked, such as longwall, room-and-pillar, etc.

planar
 * Lying or arranged as a plane or in planes, usually implying more or less parallelism, as in bedding or cleavage. It is a two-dimensional arrangement, in contrast to the one-dimensional linear arrangement.

planar cross-bedding
 * a. Cross-bedding in which the lower bounding surfaces are planar surfaces of erosion. It results from beveling and subsequent deposition.

b. Cross-bedding characterized by planar foreset beds.

planar element
 * A fabric element having two dimensions that are much greater than the third; e.g., bedding, cleavage, and schistosity. CF: linear element.

planar flow structure
 * See: platy flow structure.

planar gliding
 * Uniform slippage along plane surfaces.

planar structure
 * See: platy flow structure.

planation
 * The widening of valleys through lateral corrasion by streams after they reach grade and begin to meander and form floodplains. Also, by the extension, the reduction of divides and the merging of valley plains to form a peneplain; peneplanation.

plane
 * a. Any roadway, generally inclined but not necessarily so, along which ore or workers are conveyed by mechanical means from one bed to another or to a lower elevation in the same bed. See also: bedding plane; fault plane; slope.

b. A road on the natural floor of a seam. c. A two-dimensional form that is without curvature; ideally, a perfectly flat or smooth surface. In geology the term is applied to such features as a bedding plane or a planation surface. Adj: planar. See also: surface. d. In crystallography, a plane of symmetry dividing a crystal structure into two mirror images. See also: symbols of crystal faces. e. A level surface bounded by straight lines, such as the faces of crystals.

plane course
 * Scot. In the direction facing the joint planes. Syn: on plane.

plane engineer
 * See: slope engineer.

plane fault
 * A fault with a surface that is planar rather than curved.

plane figure
 * A plane surface bounded either by straight lines or curved lines or by a combination of straight and curved lines.

plane group
 * The 17 possible combinations of symmetry elements which may coexist in 2 dimensions. CF: space group.

plane man
 * See: incline man.

plane of saturation
 * See: water table.

plane of stretching
 * A low-angle gravity (normal) fault resulting from stretching of the solidified top of an igneous intrusion.

plane of symmetry
 * Any plane which divides a crystal, crystal structure, or crystal symmetry such that each side is a mirror reflection of the other. Represented as m or 2 and graphically as a solid or heavy line. Syn: mirror plane.

plane or rectangular coordinate
 * Either of two perpendicular distances of a point from a pair of rectangular coordinate axes.

plane-polarized light
 * Light with its electric vector confined to a plane.

planer
 * a. First developed as a fixed-blade device for continuous longwall mining of narrow seams of friable coal, this machine is pulled along the coal face, planing a narrow cut. Vibrating-blade planers were designed later in an attempt to apply the technique to harder coal; they have also been experimented with in the phosphate mines in western Montana and northern Idaho.

b. A machine provided with a cutting tool having lateral and vertical adjustment that is widely used in stone trimming. Both sides and tops of blocks may be planed to desired dimensions. Some planers may be adjusted to cut curved forms.

planerite
 * A triclinic mineral, Al (sub 6) (PO (sub 4) ) (sub 2) (PO (sub 3) OH) (sub 2) (OH) (sub 8) .4H (sub 2) O ; turquoise group.

plane schistosity
 * A type of schistosity characterized by the arrangement of tabular and prismatic grains in parallel planes.

plane shear
 * One of four types of slope failure. Plane shear failure results when a natural plane of weakness, such as a fault, a shear zone, or bedding plane exists within a slope and has a direction such as to provide a preferential path for failure. Large intact portions of the slope rock may slide along this plane surface.

plane strain
 * A state of strain in which all displacements that arise from deformation are parallel to one plane, and the longitudinal strain is zero in one principal direction.

plane stress
 * A state of stress in which one of the principal stresses is zero.

plane surveying
 * Ordinary field and topographic surveying in which Earth curvature is disregarded and all measurements are made or reduced parallel to a plane representing the surface of the Earth. The accuracy and precision of results obtained by plane surveying may decrease as the area surveyed increases in size. CF: geodetic surveying.

plane table
 * a. An instrument for plotting the lines of a survey directly from the observations; consisting essentially of a drawing board mounted on a tripod and fitted with a ruler that is pointed at the object observed, usually with the aid of a sighting device, such as a telescope.

b. An inclined ore-dressing table.

planetary geared drum
 * A drum containing planetary gearing that is used to control the motion of the rope drums on certain types of mining machines. In planetary gearing, which is used when a large ratio of speed reduction with only a few operating gears is required, some or all of the gear wheels in the train of mechanism have a motion about an axis and a revolution about the same axis.

planetary lap
 * A type of machine lap employing a number of geared workholders that rotate with an epicyclic motion between two stationary lapping plates. The crystals being lapped, when contained in pentagonal holes in the workholder, have an imposed rotatory motion. Also known as the Hunt-Hoffman lap or Bendix lap.

planetary mill
 * Mill used for making very large reductions on slabs by one pass through the mill. The mill consists of two large plain rolls, each surrounded by many small work rolls.

planetary set gear
 * A gearset consisting of an inner (sun) gear, an outer ring with internal teeth, and two or more small (planet) gears meshed with both the sun and the ring.

plane tender
 * See: slope engineer.

planet gearing
 * Gearing in which one gear wheel revolves around another.

planimeter
 * An instrument for measuring the area of any plane figure by passing a tracer around its boundary line.

planimetric analysis
 * Analysis of patterns in a fabric diagram based on distribution of points and areal comparisons.

planimetric map
 * A map that presents only the relative horizontal positions of natural or cultural features, by lines and symbols. It is distinguished from a topographic map by the omission of relief in measurable form. Syn: line map.

planimetry
 * a. The measurement of plane surfaces; e.g., the determination of horizontal distances, angles, and areas on a map.

b. The plan details of a map; the natural and cultural features of a region (excluding relief) as shown on a map.

planisher
 * A device for flattening thin sections cut for microscopic examination.

plank timbering
 * The lining of a shaft with rectangular plank frames. See also: box timbering.

plankton
 * The whole community of rifting small plants and animals in layers of the water. This term is frequently used to describe all life forms, regardless of size, which have no means of significant self-locomotion. This community can be divided into the phytoplankton (plants) and the zooplankton (animals).

plankton bloom
 * The rapid growth and multiplication of plankton, usually plant forms, producing an obvious change in the physical appearance of the sea surface, such as coloration or slicks. Also called sea bloom; florescence.

planktonic
 * Relating to the chiefly simple types of floating and surface-dwelling forms of organisms of the ocean waters.

plank tubbing
 * The lining of a shaft with planks, spiked on the inside of curbs. See also: tubbing.

planning
 * The predesign of the detailed layout, main roadways, and workings of a mine or group of mines. The scheme usually involves the introduction of mechanical equipment for the working and transport of the coal or mineral. The selection of mining methods and machines properly adapted to the local conditions is part of planning.

planning engineer
 * A mining engineer responsible for mine planning. The engineer is attached to the planning department of a large mine or a group of smaller mines and is qualified by training, experience, and technical qualifications to envisage new development work and coordinate the ideas of other experts such as a mechanization engineer, ventilation engineer, mining geologist, etc.

planometric projection
 * Pictorial view of an object showing it in plan with oblique lines showing the front, side, and thickness. See also: projection.

planosol
 * A great soil group in the 1938 classification system; an intrazonal, hydromorphic group of soils having a leached surface layer above a definite clay pan or hardpan. These soils develop on nearly flat upland surfaces under grass or trees in a humid to subhumid climate.

plant
 * a. The shaft or slope, tunnels, engine houses, railways, machinery, workshops, etc., of a colliery or other mine.

b. To place gold or any valuable ore in the ground, in a mine, or the like to give a false impression of the richness of the property. To salt, as to plant gold with a shotgun. See also: salting a mine. c. In mining, the mechanical installations, machines, and their housings. Earthworks are sometimes loosely included. d. Used to include the machinery, derricks, railway, cars, etc., employed in tunnel work.

plant mix
 * The process of soil stabilization in which the soil is carried to a stationary mixer, returned to the site after mixing and then spread. CF: mix-in-place.

plant-mixed concrete
 * Concrete that is mixed at a central mixing plant and delivered to a site in special equipment designed to prevent its segregation.

plant-mix method
 * A method of preparing aggregates for bituminous surfaces in which aggregates and bitumen are combined in a plant situated at the road or at a relatively long distance from the road. Also known as the premixed method.

plant scrap
 * Scrap metal produced in the plant itself; e.g., sprues and gates in a foundry or defective ingots and hot tops in a steel mill. Also called home scrap.

plasma
 * a. Gas comprising equal amounts of positively and negatively charged particles; a fourth state of matter (solid, liquid, gas, plasma) capable of conducting magnetic force.

b. A bright-, leek-, to emerald-green subtranslucent variety of cryptocrystalline (chalcedonic) quartz. The green color is attributed to chlorite. CF: bloodstone; heliotrope. c. That part of a soil which can be or has been moved, reorganized, and/or concentrated by soil-forming processes.

plasma jet
 * a. A jet formed by passing a high-speed current of nitrogen or a mixture of nitrogen and hydrogen over a tungsten electrode placed in a specially designed narrow orifice in a cutting torch. An arc is struck between this electrode and the earthed nozzle of the torch, which is cooled by a water jacket. When a plasma jet is used to cut rock, two separate zones of action can be expected.

b. Ionized gas produced by passing an inert gas through a high-intensity arc, causing temperatures up to tens of thousands degrees centigrade.

plastering
 * See: mudcapping.

plaster mill
 * A machine consisting of a roller or set of rollers for grinding lime or gypsum to powder.

plaster pit
 * Derb. A gypsum mine.

plaster shooting
 * a. A surface blasting method used when no rock drill is available or is not necessary. It consists of placing a charge of gelignite, primed with safety fuse and detonator, in close contact with the rock or boulder and covering it completely with stiff damp clay. The charges vary from 8 to 16 oz/yd (super 3) (297 to 593 g/m (super 3) ) of rock. See also: popping; snakeholing.

b. A form of secondary blasting in which the explosive is detonated in contact with the rock without the use of a shothole. See also: secondary blasting; mudcapping.

plaster stone
 * See: gypsum.

plastic
 * Said of a body in which strain produces continuous, permanent deformation without rupture. CF: elastic.

plastic and semiplastic explosive
 * Any of several explosives used for commercial purposes. The consistency is such that the explosive can be shaped by moderate pressure to fill a drill hole. The difference between plastic and semiplastic form is primarily dependent on the difference in equipment which has been found necessary in manufacturing cartridges of the explosive. The viscosity of the plastic type makes it possible to produce cartridges by a process of extrusion through tubes.

plastic clay
 * Any clay, but chiefly kaolinite, which, when mixed with water, is easily shaped and retains this shape until fired.

plastic deformation
 * a. Permanent deformation of the shape or volume of a substance, without rupture. It is mainly accompanied by crystal gliding and/or recrystallization. Syn: plastic flow; thixotropy. CF: plastic strain.

b. Deformation by one or both of two grain-scale mechanisms: slip, and twinning. This is a metallurgical definition, increasingly used by geologists. Sometimes called crystal plasticity. c. Rheological term for deformation characterized by a yield stress, which must be exceeded before flow begins. d. An elastic deformation of brittle minerals--such as olivine under mantle conditions, or quartz, during metamorphism; deformation occurs along well-defined crystallographic planes in specific directions, which may be preserved as thin deformation lamellae or as deformation twinning. It may be annealed out by recrystallization. CF: elastic deformation. e. Irreversible deformation of metallic minerals, such as gold or copper. See also: malleability.

plastic design
 * The design of steel or reinforced-concrete structural frames which is based on the assumption that plastic hinges form at points of maximum bending moment. See also: elastic design; plastic modulus.

plastic explosive
 * See: plastic and semiplastic explosive.

plastic firebrick
 * A common term for both high duty and super-duty fire clay plastic refractories.

plastic flow
 * See: plastic deformation.

plastic fracture
 * The breakage of a solid material under load when being permanently deformed.

plastic igniter cord
 * A corklike device for lighting a safety fuse. When the cord is ignited an intense flame passes along its length at a uniform rate and ignites the blackpowder core of an ordinary safety fuse. Two types are made: the fast has a nominal burning speed of 1 s/ft (3.3 s/m); the other is about 10 times as slow.

plasticity
 * The property of a material that enables it to undergo permanent deformation without appreciable volume change, elastic rebound, or rupture. See also: plastic deformation; plastic flow; plastic limit; plastic soil; plastic state; plasticity index.

plasticity index
 * The water-content range of a material at which it is plastic, defined numerically as the liquid limit minus the plastic limit. CF: Atterberg limits; plastic limit.

plasticizer
 * A material, usually organic, capable of imparting plastic properties to nonplastics or improving the plasticity of ceramic mixtures. Syn: wetting agent.

plastic limit
 * a. The water-content boundary beyond which a soil can be rolled into a thread approx. 3 mm in diameter without crumbling, i.e., beyond which it is plastic.

b. The water content of a soil or clay material corresponding to an arbitrarily defined boundary between a plastic and a semisolid state. CF: Atterberg limits; plasticity index.

plastic modulus
 * A factor used in the plastic design of steel structures. It is a constant for each particular shape of section. See also: plastic design.

plastic soil
 * a. A soil that can be rolled into 1/8-in (1.6-mm) diameter strings without crumbling.

b. A soft, rubbery soil. c. A soil that exhibits plasticity.

plastic solid
 * A solid that undergoes change of shape continuously and indefinitely after the stress applied to it passes its elastic limit.

plastic state
 * The range of consistency within which a soil exhibits plastic properties. Also called plastic range.

plastic strain
 * In rocks, which are composed of many crystals commonly belonging to several mineral species, the term applies to any permanent deformation throughout which the rock maintains essential cohesion and strength regardless of the extent to which local microfracturing and displacement of individual grains may have entered into the process. CF: plastic deformation.

plastic tamping rod
 * A tamping rod or stemmer, of a rigid nature, made from plastic possessing suitable dielectric properties. A plastic conducive to the building up of heavy charges of static electricity is unsuitable.

plastic tooling
 * Dies, jigs, and fixtures for metal forming, boring, assembly, and checking; made at a saving of time and labor, of laminated and cast components, and cemented into highly stable industrial tools, chiefly with epoxy and some with polyester resins. Epoxies are strong adhesive resins, particularly useful because of their low shrinkage factor. Polyesters have a cost advantage and are easy to handle.

plastic yield
 * The term commonly applied to plastic deformation.

plastic zone
 * In explosion-formed-crater nomenclature, this zone differs from the rupture zone by having less fracturing and only small permanent deformations. There is no distinct boundary between the rupture and plastic zones.

Plast-Sponge
 * High-quality iron powder made by reduction of iron oxide; used in powder metallurgy.

plat
 * a. The map of a survey in horizontal projection, such as of a mine, townsite, etc.

b. A diagram drawn to scale showing land boundaries and subdivisions, together with all data essential to the description of the several units. A plat differs from a map in that it does not show additional cultural, drainage, and relief features. c. A platform, floor, or surface in or about a mine used esp. for loading and unloading ore, etc.

plate
 * a. A flat iron or steel sheet laid around a mine-shaft collar, at the shaft bottom, or at any level station, to enable mine cars and other equipment to be easily turned and moved about. Also, a cast-iron plate with a circular ridge on which mine rail cars are turned at the junction of roads.

b. A horizontal timber laid on a floor or sloping wall to receive a framework of timbers. c. A torsionally rigid thin segment of the Earth's lithosphere, which may be assumed to move horizontally and adjoins other lithosopheric plates along zones of seismic activity. See also: plate tectonics.

plate amalgamation
 * Use of copper or copper-alloy plates coated with enough mercury to form a soft adherent film, in order to trap gold from crushed ore pulp as it flows over the plates. The resulting amalgam, containing up to 40% metallic gold, is periodically scraped off and more mercury is added to the film.

plate-and-frame filter
 * A filter press consisting of plates with a gridiron surface alternating with hollow frames, all of which are held by means of lugs, on the press framework. The corners of both frames and plates are cored to make continuous passages for pulp and solution; the filter cloth is placed over the plates. The pulp passageway connects with the large, square opening in the frame; the solution and passageways connect with the gridiron surface of the plate. The Dehne and the Merrill are well-known types.

plate apron feeder
 * An automatic arrangement by which coal or ore is fed forward on steel plates forming segments linked together in an endless chain. See also: plate feeder.

plateau
 * Broadly, any comparatively flat area of great extent and elevation; specif. an extensive land region considerably elevated (more than 150 to 300 m in altitude) above the adjacent country or above sea level; it is commonly limited on at least one side by an abrupt descent, has a flat or nearly smooth surface but is often dissected by deep valleys and surmounted by high hills or mountains, and has a large part of its total surface at or near the summit level. A plateau is usually higher and has more noticeable relief than a plain (it often represents an elevated plain), and it is usually higher and more extensive than a mesa; it may be tectonic, residual, or volcanic in origin. See also: tableland. CF: mesa.

plateau basalt
 * A term applied to those basaltic lavas that occur as vast composite accumulations of horizontal or subhorizontal flows, which, erupted in rapid succession over great areas, have at times flooded sectors of the Earth's surface on a regional scale. They are generally believed to be the product of fissure eruptions. CF: shield basalt. Syn: flood basalt.

plateau gravel
 * A sheet, spread, or patch of surficial gravel, often compacted, occupying a flat area on a hilltop, plateau, or other high region at a height above that normally occupied by a stream-terrace gravel. It may represent a formerly extensive deposit that has been raised by earth movements and largely removed by erosion.

plate bearing test
 * A method by which the load bearing capacity of a soil may be estimated. See also: ultimate bearing pressure.

plate cleaner
 * A device for cleaning raw coal which uses the difference in the coefficient of resilience or friction between clean coal and an inclined plate, commonly of steel, and that between refuse and the plate to allow the clean coal to jump over a gap while the refuse falls through.

plate conveyor
 * A conveyor in which the carrying medium is a series of steel plates, each in the form of a short trough, joined together with a slight overlap to form an articulated band. The plates are attached either to one center chain or to two side chains. The chains connect rollers running on an angle-iron framework and transmit the drive from the driveheads that can be installed at intermediate points as well as at the head or tail ends. A plate conveyor can negotiate bends down to about 20 ft (6.1 m) radius; available in widths 400, 540, and 640 mm with running speeds from 3 to 4 ft/s (0.9 to 1.2 m/s) with a carrying capacity from 100 to 400 st/h (90.7 to 362.8 t/h). Syn: steel plate conveyor.

plate coordinate
 * In photographic mapping, either of two rectangular coordinates measured on a photograph with reference to the principal point as origin.

plated crystal
 * A crystal with a conductive surface film of gold, silver, aluminum, or other metal produced by cathode sputtering, evaporation, or chemical methods. The films, to which lead wires may be soldered, take the place of the conventional clamped metal electrodes.

plate feeder
 * The mechanical plate feeder is a device for feeding material at a fixed and uniform rate. It is generally applied at the tail end of a conveyor or elevator which feeds a plant, but may be applied to feeding any other single unit. It relieves the pressure and drag, with the consequent unnecessary wear on the belt, which is ordinarily experienced if feeding from a hopper directly to a belt. It not only cuts maintenance costs by eliminating uneven wear, but increased output can be obtained by steady feeding. This type of feeder also handles wet aggregate. See also: disk feeder; reciprocating feeder.

plate former
 * Used for lining shafts, winzes, and rises; usually constructed of comparatively thin steel sheeting, stiffened around the edges with angles. Plates should be of such size that they can be conveniently handled in the skips or buckets used for sinking.

plate girder
 * A built-up riveted or welded steel girder, having a deep vertical web plate, with a pair of angles riveted along each edge to act as compression and tension flanges. For heavier loads, flange plates are riveted or welded to the angles.

plate roll
 * A smooth roll for making sheet iron or plate iron, as distinguished from iron having grooves for rolling rails, beams, etc.

plate tectonics
 * A theory of global tectonics in which the lithosphere is divided into a number of plates whose pattern of horizontal movement is that of torsionally rigid bodies that interact with one another at their boundaries, causing seismic and tectonic activity along these boundaries.

plate tongs
 * Tongs for grasping and handling iron or steel plates.

platform
 * a. The place on top of a breaker where the freshly mined coal is weighed by a weigh boss just before it is dumped into the machinery.

b. A wooden floor on the side of a gangway at the bottom of an inclined seam, to which the coal runs by gravity, and from which it is shoveled into mine cars. c. A plank or mesh steel-covered level area at the base of a drill tripod or derrick, used as a working space in front of a drill machine around the collar of the borehole. Sometimes the platform is large enough to act as a foundation and anchor for the drill machine. d. A scaffold. e. A wood mat used in sets to support machinery on soft ground. Also called pontoon. f. An operator's station on a large machine, particularly on rollers. g. In the breaker, a flat or slightly inclined floor covered with iron plates onto which coal is run from the main screen bars and cleaned by platform workers. h. Also a similar floored area in the tripod or derrick on which a laborer stands while working in a tripod or derrick. See also: floor.

platform gantry
 * A gantry constructed for carrying a portal crane or a similar structure.

platform hoist
 * A power-driven hoist, having a lifting capacity ranging from 200 lb (90.7 kg) to about 2-1/2 st (2.27 t), which can be raised on a loading platform up to 200 ft (61 m) high.

platina
 * a. Twisted silver wire.

b. Crude native platinum.

platinic gold
 * Said to be a native alloy containing 84.6% gold, 2.9% silver, 0.2% iron, 0.9% copper, and the remainder 11.4% platinum.

platiniridium
 * An isometric mineral, (Ir,Pt), with Ir 50% to 80% (atomic) of Ir + Pt; forms silver-white grains having sp gr, 22.6 to 22.8; (super ) Mohs hardness, 6 to 7.

platinize
 * To coat or combine with platinum, esp. by electroplating.

platinum
 * a. An isometric mineral, native platinum 4[Pt] with variable Pd, Ir, Fe, Ni; malleable; ductile; metallic; sp gr, 21.45; corrosion resistant; occurs in ultramafic rocks, quartz veins, and in placers.

b. A malleable and ductile silvery-white metal, when pure. Symbol: Pt. Occurs native, accompanied by small quantities of iridium, osmium, palladium, ruthenium, and rhodium. Used in jewelry, wire, vessels for laboratory use, and in many valuable instruments including thermocouple elements.

platinum-group metal
 * (PGM). Any of the minerals native platinum, osmium, iridium, palladium, rhodium, ruthenium, and their alloys, such as osmiridium (Ir,Os), ruthenosmiridium (Ir,Os,Ru) , rutheniridosmine (Os,Ir,Ru) , and platiniridium (Ir,Pt) . Other alloys of PGM are exemplified by stanopalliadinite, (Pd,Cu) (sub 3) Sn (sub 2) (?) ; and potarite, PdHg . Other sources of PGM are sperrylite, PtAs (sub 2) ; cooperite, (Pt,Pd,Ni)S; stibiopalladinite, Pd (sub 5) Sb (sub 2) ; braggite, (Pt,Pd,Ni)S ; vysotskite, (Pd,Ni)S ; ruthenarsenite, (Ru,Ni)As ; cuproiridsite; CuIr (sub 2) S (sub 4) ; cuprorhodsit, CuRh (sub 2) S (sub 4) ; malanite, Cu(Pt,Ir) (sub 2) S (sub 4) ; and dayingite, CuCoPtS (sub 4) . Varietal terms include plyxene and ferroplatinum for iron alloys and cuproplatinum for copper alloys.

platinum sponge
 * Metallic platinum in a gray, porous, spongy form; obtained by reducing ammonium chloroplatinate, which occludes large volumes of oxygen, hydrogen, and other gases.

platting
 * Brick laid flatwise on top of a kiln to keep in the heat.

plattman
 * In bituminous coal mining, a colloquialism of English origin for a pusher who pushes loaded mine cars onto a cage from a platt (an enlarged underground opening at the shaft where cars are gathered prior to hoisting).

plattnerite
 * a. A tetragonal mineral, PbO (sub 2) ; rutile group; dimorphous with scrutinyite; iron black; occurs in lead mines.

b. Erroneous spelling of planerite.

platy flow structure
 * An igneous rock structure of tabular sheets suggesting stratification. It is formed by contraction during cooling; the structure is parallel to the surface of cooling and is commonly accentuated by weathering. Syn: platy structure; planar flow structure.

platynite
 * A trigonal mineral, PbBi (sub 2) (Se,S) (sub 3) ; metallic; iron-black; forms thin plates like graphite; at Falun, Sweden. Also spelled platinite.

platy structure
 * See: platy flow structure.

playa
 * a. A term used in southwestern United States for a dry, vegetation-free, flat area at the lowest part of an undrained desert basin, underlain by stratified clay, silt, or sand, and commonly by soluble salts. The term is also applied to the basin containing an expanse of playa, which may be marked by ephemeral lakes. See also: salina; alkali flat; salt flat; salar. Syn: dry lake.

b. See: playa lake. c. A small, generally sandy land area at the mouth of a stream or along the shore of a bay. Etymol: Spanish, beach, shore, coast.

playa basin
 * See: bolson.

playa lake
 * A shallow, intermittent lake in an arid or semiarid region, covering or occupying a playa in the wet season but drying up in summer; an ephemeral lake that upon evaporation leaves or forms a playa. Syn: playa.

play of color
 * A pseudochromatic optical effect resulting in flashes of colored light from certain minerals, such as fire opal and labradorite, as they are turned in white light. Periodic spacings of phases with slightly differing refractive indices act as optical diffraction gratings in these minerals. CF: fire; opalescence; pseudochromatism. Syn: schiller.

plenargyrite
 * See: matildite.

plenum
 * a. A system of ventilation in which air is forced into an inclosed space, such as a room or a caisson, so that the outward pressure of air in the space is slightly greater than the inward pressure from the outside, and thus leakage is outward instead of inward.

b. A mode of ventilating a mine or a heading by forcing fresh air into it. c. Use of compressed air to hold soil from slumping into an excavation.

pleochroic
 * See: pleochroism.

pleochroic halo
 * a. A minute zone of color or darkening surrounding and produced by a radioactive mineral crystal or inclusion.

b. Any of the concentrically colored aureoles in minerals--e.g., micas, fluorite, and cordierite--centered by minute grains of minerals containing radioactive elements, such as zircon and monazite. This discoloration results from crystal structural radiation damage from alpha decay.

pleochroism
 * a. The property of exhibiting different colors in different directions by transmitted polarized light.

b. More precisely, the property of absorbing differently, light that vibrates in different directions in passing through a crystal. If the crystal is uniaxial the change of color is called dichroism; if the crystal is biaxial, the change of color is called pleochroism. c. The property of birefringent crystals (minerals) to absorb various wavelengths of light differentially depending on the vibration direction of the light within the crystal. Thus a mineral displaying pleochroism shows various colors or tints when it is traversed by plane polarized light and the orientation of the crystal is varied with respect to the plane of polarization. It is a common and diagnostic property of many minerals, and is easily observed under the petrographic microscope or a dichroscope. d. The capacity of strongly anisotropic minerals to change absorption colors with changing electric vector in plane-polarized light; e.g., as seen with a polarized-light microscope. Uniaxial minerals may be dichroic and biaxial ones trichroic. Qualitative pleochroism is change of intensity in the same color; quantitative pleochroism shows change of color with change of orientation. Adj: pleochroic. CF: dichroism; trichroism. Syn: polychroism.

pleomorphism
 * See: polymorphism. Adj. pleomorphous

pleonaste
 * See: ceylonite.

plessite
 * A fine grained intergrowth of kamacite and taenite.

pliable armored cable
 * A flexible cable having collective armor comprising stranded groups of fine, galvanized, steel wires.

pliable support
 * A support composed of elastic materials that either yields to the roof pressure, or permits the subsidence of the roof without the support being completely destroyed and losing its significance.

plication
 * Intense, small-scale folding. Adj: plicated. CF: crenulation.

ploat
 * Eng. To dress down or remove loose stone from the roof or sides.

plombierite
 * A mineral, Ca (sub 5) H (sub 2) Si (sub 6) O (sub 18) .6H (sub 2) O(?).

plot mark
 * A mark made in a bit mold, bit die, or blank bit where a pip or hole is drilled to receive or to encompass a diamond.

plotting instrument
 * A large drawing machine by means of which stereoscopic pairs of vertical photographs can be viewed in conjunction with their ground control points and mechanically translated into accurate maps.

plotting scale
 * A scale used for setting off the lengths of lines in surveying.

plow
 * a. In coal mining, a cutter loader with knives or blades, which is pulled along the longwall face by a powerful chain. The broken coal is loaded onto an armored flexible conveyor which, with the aid of hydraulic rams, holds the plow up to the coal face and causes the knives to bite into the coal as they are pulled along. The plow is a continuous mining machine. See also: plow-type machine.

b. Applied to V-shaped belt scrapers that are attached to the belt conveyor frame and which press against the return belt. They are intended to remove coal or other material that might stick to the return belt and be crushed as the belt passes over the driving rolls or the return pulley.

plow cut
 * See: V-cut.

plow deflector
 * a. A steel plate attached to the end of a cutter loader for deflecting cut coal onto the face conveyor.

b. A device for removing or diverting the dust and dirt off a belt conveyor and thus prevent it being carried back along the return belt.

plow steel
 * A high-tensile steel used in the manufacture of hoisting ropes.

plow-type machine
 * Plows may be divided into two classes: (1) machines that peel the coal to a depth of from 1 to 12 in (2.54 to 30.5 cm) by knives of various designs and the cut coal is then loaded onto a heavy type scraper chain conveyor; and (2) machines that peel a thin slice up to 2 in (5.1 cm) in thickness, by knives attached to each end of a steel box, and the coal is dragged along the face inside the box. From the aspect of speed of travel, plows may be divided into: (1) slow-moving types of 10 to 20 ft/min (3.0 to 6.1 m/min), which remove a thicker slice; and (2) fast-moving types at about 80 ft/min (24.4 m/min), which take a relatively thin slice. See also: Anbauhobel; continuous mining; Lobbe Hobel.

plucking
 * a. Describes the sudden jerking or plucking on heavy endless-rope haulage when the rope again takes the load, following rope coils. Instead of slipping smoothly sideways, the rope tends to stick until the pressure of oncoming coils overcomes the friction; these slip suddenly, producing a momentary slackening followed by a sudden jerk or pluck as the rope again takes the load. This may loosen chains or clips and cause derailments and runaway sets.

b. The disruption of blocks of rock by a glacier or stream.

plug
 * a. A watertight seal in a shaft formed by removing the lining and inserting a concrete dam, or by placing a plug of clay over ordinary debris used to fill the shaft up to the location of the plug.

b. See: hoisting plug. c. A steel cylinder placed inside the annular opening in a coring bit to convert it for use as a noncoring bit. The face of the plug may or may not be provided with serrations, inset diamonds, or other types of cutting edges. d. See: block. e. See: cartridge. f. A cylindrical piece of wood or an expandable metal apparatus placed in a borehole to act as a base into which the drive wedge of a borehole deflection device is driven. g. Small wooden pin driven into a hole in the rock roof of a tunnel. The axis of the tunnel is marked on such plugs by tacks, or by small iron hooks from which a plummet lamp may be suspended for sighting upon. h. To plug a well by cementing a block inside casing or capping the well with a metal plate. i. Any block installed within casing to prevent movement of fluids. j. A steel wedge used in quarrying dimension stone. See: plug-and-feather method. k. A vertical, pipelike body of magma that represents the conduit to a former volcanic vent. CF: neck.

plug-and-feather hole
 * A hole drilled for the purpose of splitting a block of stone. These holes are usually in rows. The plug is a slightly wedge-shaped piece of iron driven between two L-shaped irons, or feathers, inserted in the hole.

plug-and-feather method
 * A method used in quarrying to reduce large masses of stone to smaller size. By using a hammer drill, a row of shallow holes is made along the line where a break is desired. The feathers consist of two iron strips flat on one side for contact with the wedge, and curved on the other to fit the wall of the drill hole. They are placed in the hole and the plug (a steel wedge) is placed between them. They are sledged lightly in succession until a fracture appears. Wherever possible, such fractures are made parallel with the rift of the stone. Syn: multiple wedge. See also: plug.

plug bit
 * a. A diamond bit that grinds out the full width of a hole.

b. A noncoring diamond-set bit that can be in the form of a bullnose bit, pilot bit, or concave bit. Also called bullnose bit; concave bit; noncore bit; pilot bit.

plug box
 * Eng. A wooden water pipe used in coffering.

plug drill
 * A stonecutter's percussion drill.

plugged
 * a. A borehole that has been filled or capped with a long plug, or in which a plug has been inserted.

b. Cracks or openings in the rocks in the walls of a borehole that have been filled or sealed with cement or other substances. c. A borehole that has been drilled with a plug or noncoring bit. d. A blocked core barrel or bit. e. A coring bit in which a plug has been inserted. See also: plug.

plugged bit
 * a. See: noncoring bit.

b. A core bit, the annular opening of which is tightly closed or blocked by a piece or the impacted fragments of a core.

plugged crib
 * A curb supporting the walling in a shaft and is itself supported on plugs or bolts driven into the ground around the shaft. The crib may be removed when the walling from below is carried up to it. See also: strata bolt.

plugging
 * a. The stopping of the flow of water into a shaft by plugs of clay.

b. The material used, the act, or the process of inserting a plug in a borehole to fill it or the cracks and openings in the borehole sidewalls. c. The act or process of drilling a borehole with a noncoring bit. d. The practice of filling holes and cavities in castings with porous silicate mixture (cast iron filler) before the application of cover coats. The filler must be firmly forced into the casting holes, since any entrapped air beneath the filler will expand during firing and force the material out causing blowholes.

plughole
 * a. A passageway that is left open, while working on an explosion-proof stopping, for the purpose of maintaining the ventilation of the fire area at or as near the normal quantity as possible, to prevent any increase in the combustible gases content in the air. After the stopping is completed, this hole is plugged up with sandbags in order to completely seal off the mine area. The plughole is generally a tapered passageway of about 3.5 ft (1.1 m) square at the inby side of the stopping and 2.5 ft (0.76 m) square at the outby side.

b. See: block hole.

plughole stopping
 * A stopping in which the floor and the sidewalls of the passage are built of sandbags, and the roof may be the roof of the roadway or covering boards used between the webs of steel arches, or preferably, corrugated steel sheeting used as lagging behind steel arches. The plughole or passage is generally tapered from the inby end from 3 to 3.5 ft (0.9 to 1.1 m) square to 2.5 ft (0.76 m) square so that, in the event of an explosion, the plug of sandbags in the passage is subjected to a wedging action assisting to retain the plug in place. The plughole may be placed in the most convenient position and although this is often at the top, it is sometimes placed to the side and reasonably near the floor.

plugman
 * See: pumping engineer.

plug shot
 * Scot. A small charge exploded in a hole to break up a stone of moderate size.

plug valve
 * A valve or cock opened or closed by the turning of a plug, usually conical in shape. Not to be confused with needle valve or globe valve.

plum
 * a. A large random-shaped stone dropped into a large-scale mass of concrete to economize on the volume of the concrete.

b. An old form of plumb.

plumb
 * a. See: vertical.

b. See: plumb bob; plumbline. c. To carry a survey into a mine through a shaft by means of heavily weighted fine wires hung vertically in the shaft. The line of sight passing through the wires at the surface is thus transferred to the mine workings. An important piece of work: in mine shafts, and in transferring courses or bearings from one level to another.

plumbago
 * a. A special quality of powdered graphite used to coat molds, and in a mixture with clay, to make crucibles.

b. See also: black lead; graphite. c. Impure graphite or graphitic rock. d. Minerals resembling graphite; e.g., molybdenite.

plumbago crucible
 * Highly refractory crucible composed of a mixture of about equal parts of refractory clay and graphite.

plumb bob
 * a. A small weight or bob, hanging at the end of a cord, which under the action of gravity is oriented in a vertical direction. Also called a plummet.

b. A pointed weight hung from a string. Used for vertical alignment.

plumber's dope
 * A soft sealing compound for pipe threads.

plumbic
 * Of, pertaining to, or containing lead, esp. in its higher valence. CF: plumbous.

plumbiferous
 * Containing lead.

plumbing
 * Transferring a point at one level to a point vertically below or above it by means of a weight (plumb bob or plummet) suspended at the end of a string or wire (plumbline). See also: centering of shaft; string survey.

plumbline
 * A device used to produce a vertical line between a survey instrument and the reference point over (or sometimes under, in underground work) which it is set. Special plumblines are used in a vertical shaft to transfer a fixed or an azimuth angle from the surface to underground workings for the purpose of orientation. Also known as plumb bob; plummet. See also: Weisbach triangle.

plumbocalcite
 * A variety of calcite containing a small amount of lead carbonate.

plumboferrite
 * A trigonal mineral, PbFe (sub 4) O (sub 7) ; black; at Jakobsberg, Sweden.

plumbogummite
 * A trigonal mineral, PbAl (sub 3) (PO (sub 4) ) (sub 2) (OH) (sub 5) .H (sub 2) O ; crandallite group; forms yellow to brown encrustations; in Cumberland, United Kingdom.

plumbojarosite
 * A trigonal mineral, PbFe (sub 6) (SO (sub 4) ) (sub 4) (OH) (sub 12) ; alunite group; forms minute brown tabular crystals with rhombohedral cleavage.

plumbomicrolite
 * An isometric mineral, (Pb,Ca,U) (sub 2) Ta (sub 2) O (sub 6) (OH); pyrochlore group. It occurs in greenish-yellow and orange masses and octahedra from Kivu, Zaire.

plumbous
 * Of, pertaining to, or containing lead, esp. in its lower valence. CF: plumbic.

plumb pneumatic jig
 * Mineral concentrator in which air is pulsed upward through a porous deck by means of a rotary valve.

plumb post
 * One of the vertical posts at the side of a tunnel resting on sills and carrying the wallplates; collectively, they support the tunnel roof by means of centering.

plumites
 * A feathery variety of jamesonite. See also: plumose antimony.

plummet
 * See: plumbline.

plumose
 * Having a feathery appearance.

plumose antimony
 * A feather-ore variety of jamesonite or boulangerite; also called feather ore. Also spelled plumites, plumosite.

plumose mica
 * A feathery variety of muscovite.

plumosite
 * A feathery variety of jamesonite or boulangerite.

plump
 * Corn. A corruption of the word pump.

plum-pudding stone
 * See: puddingstone.

plunge
 * a. The vertical angle between a horizontal plane and the line of maximum elongation of an orebody.

b. The inclination of a fold axis or other linear structure, measured in the vertical plane. CF: apparent plunge; dip. c. To set the horizontal cross wire of a theodolite in the direction of a grade when establishing a grade between two points of known level. d. To reverse the direction of the telescope of a theodolite by rotating it 180 degrees about its horizontal axis. Syn: transit.

plunger
 * a. In blasting, a rod designed for thrusting into a drill hole and ascertaining the position of a cartridge.

b. The piston of a force pump. c. A piston and its attached rod.

plunger bucket
 * A pump piston without a valve. Also called plunger lift.

plunger case
 * The pump barrel, or cylinder, in which a solid piston or plunger works. Also called pole case.

plunger jig washer
 * A washer in which water is forced upward and then downward through a screen by the action of a plunger in an adjoining compartment. Although these machines are still in use, the term "jig washer" is now applied to the fixed-screen, air-pulse jig, which is directly descended from the first Baum washer used in 1892. See also: jig washer; pneumatic jig.

plunger lift
 * Scot. A pump and attached column of pipes, that raises water by means of a ram or piston.

plunger press
 * A press in which the pressure is applied by a plunger, with a reciprocating motion, to charges of feed contained in molds in a vertical or horizontal table.

plunger pump
 * a. Reciprocating pump used for moving water or pulp, in which a solid piston displaces the fluid.

b. A displacement-type pump may be of various types, such as: (1) the triplex pump, a vertical or horizontal, single-acting plunger type for small heads with three single-acting cylinders in the pump frame driven by a motor mounted on the outside of the frame and connected to the crankshaft of the pump through gearing; (2) the quadruplex or quintuplex pump, a pump having four or five cylinders; and (3) the duplex pump, a crank-and-flywheel type for high heads, with double-acting plungers.

plunger-type washbox
 * A washbox in which pulsating motion is produced by the reciprocating movement of a plunger or piston. Syn: piston-type washbox.

plus distance
 * Fractional part of 100 ft or m used in designating the location of a point on a survey line--such as, 4+47.2, meaning 47.2 ft or m beyond Station 4; or 447.2 ft or m from the initial point, measured along a specified line.

plush copper ore
 * See: chalcotrichite; cuprite.

plus mesh
 * The portion of a powder sample retained on a screen of stated size.

plus sight
 * See: backsight.

pluton
 * A body of medium- to coarse-grained igneous rock that formed beneath the surface by crystallization of a magma.

plutonic
 * a. Pertaining to igneous rocks formed at great depths. CF: hypabyssal.

b. Pertaining to rocks formed by any process at great depth. Syn: abyssal; deep seated; hypogene.

plutonic metamorphism
 * Deep-seated regional metamorphism at high temperatures and pressures, often accompanied by strong deformation; batholithic intrusion with accompanying metasomatism, infiltration, and injection (or, alternatively, differential fusion or anatexis) is characteristic. CF: injection metamorphism.

plutonic ore deposit
 * Collectively, the major group of ore deposits of magmatic origin that have been formed under abyssal conditions.

plutonic rock
 * Igneous rock formed deep within the Earth under the influence of high heat and pressure, hypogene rocks; distinguished from eruptive rock formed at the surface.

plutonic series
 * A series of different igneous rocks that evolved from the same original magma through various differentiation stages.

plutonism
 * a. The obsolete belief that all of the rocks of the Earth solidified from an original molten mass. CF: neptunism.

b. A general term for the phenomena associated with the formation of plutons.

pluviometer
 * See: rain gage.

ply
 * a. U.K. A thin band of shale lying immediately over a coal seam.

b. U.K. A rib or successive ribs; e.g., of clayband with very thin partings. c. Limy ply; a limestone bed; Edinburgh, U.K.

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