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Appendix:Dictionary of Mining, Mineral, and Related Terms/R/2

reach
 * a. An arm of the sea extending up into the land; e.g. an estuary or bay.

b. A continuous and unbroken expanse or surface of water or land. c. An unstated but specific distance; an interval. d. The length of a channel, uniform with respect to discharge, depth, area, and slope. e. The length of a channel for which a single gage affords a satisfactory measure of the stage and discharge. f. The length of a stream between two specified gaging stations. g. A relatively long, straight section of water along a lake shore; also, a narrow arm of a lake, reaching into the land. h. A straight, continuous, or extended part of a stream, viewed without interruption (as between two bends) or chosen between two specified points; a straight section of a restricted waterway, much longer than a narrows.

reactance
 * The part of the impedance of an alternating-current circuit that is due either to capacitance or inductance or to both and that is expressed in ohms.

reaction border
 * See: reaction rim; corona.

reaction curve
 * See: cotectic line.

reaction line
 * See: cotectic line.

reaction pair
 * Any two minerals, one of which crystallizes at the expense of the other by reaction with a melt; esp. two adjacent minerals in a reaction series.

reaction principle
 * A relationship between liquid and crystals during crystallization, esp. during fractionation, whereby crystals and liquid change composition in response to changing temperature and pressure. CF: reaction series.

reaction rim
 * A rind of one mineral surrounding another and presumably crystallized by reaction of the core mineral with surrounding fluids. CF: corrosion border. Syn: corona; kelyphytic rim; reaction border.

reaction series
 * The sequence of minerals produced by reaction between liquid and crystals during crystallization of a complex magma. Bowen's reaction series has a continuous side (calcic to alkalic plagioclase) and a discontinuous side (olivine-pyroxene-amphibole-biotite).

reaction-zone width
 * In explosives, the distance that detonation advances before the products of combustion expand by an appreciable percentage.

reactive
 * Readily susceptible to chemical change.

reactive reagent
 * Substance, solution, or gas susceptible to chemical change, or used in influencing such change.

reactive silica
 * The silica, SiO (sub 2), present within various clay minerals occurring in bauxite. During the Bayer process digestion of bauxite, this silica reacts with comparable amounts of alumina to form insoluble sodium aluminum silicate, which is lost as refinery plant residue.

reactivity
 * a. A measure of ease of ignition and response to the controls varying the rate of burning. It is used particularly in connection with fuels for transport gas producers and low volatile fuels used for open fires.

b. An assessment of the speed of reaction of a coal with oxygen under specified conditions.

readily extractable metal
 * As used in geochemical prospecting, refers to the content of a metal that can be extracted from weathered rock, overburden, or stream sediment, by weak chemical reagents. Syn: cold-extractable metal.

Reading jig
 * A plunger-type jig of relatively simple design with only a single plunger being manually controlled. The hutch compartment is round for good water distribution.

realgar
 * a. Arsenic monosulfide, AsS, contains 70.1% elemental arsenic.

b. A monoclinic mineral, AsS ; dimorphous with pararealgar; red to orange; soft; in ore veins, hot springs, and as a volcanic sublimate. Syn: red arsenic; sandarac; red orpiment.

real property
 * Includes mining claims, dumps, water rights, and ditches.

ream
 * To enlarge the hole by redrilling with a special bit.

ream back
 * The act or process of enlarging a squeezed or cave-obstructed borehole to its original size by reaming as the drill string is pulled. Syn: reverse reaming.

reamer
 * A rotary-drilling tool with a special bit used for enlarging, smoothing, or straightening a drill hole, or making the hole circular when the drill has failed to do so. See also: reaming bit; reaming shell; reamer. Also called gage stone.

reamer bit
 * See: reaming bit.

reamer shell
 * a. A cutter just above a diamond bit, used to assure a full-size hole.

b. See also: reaming shell.

reamer stone
 * See: gage stone.

reaming
 * The act or process of enlarging a borehole.

reaming bit
 * A bit used to enlarge a borehole. Also called broaching bit; pilot reaming bit. Syn: reamer; reamer bit.

reaming diamond
 * See: gage stone.

reaming pilot
 * a. See: pilot.

b. A smooth bar used to guide a reaming bit or casing bit in the hole.

reaming pilot adapter
 * An adapter or coupling in a reaming pilot assembly that attaches the flush-joint casing to the casing reaming shell and the reaming pilot horn by pin and box threads, respectively.

reaming pilot horn
 * An adapter or coupling in a reaming pilot assembly attached to the reaming pilot adapter. It passes through the reaming shell and casing bit to which is attached the pilot bit.

reaming ring
 * See: reaming shell.

reaming shell
 * a. A short tubular piece designed to couple a bit to a core barrel. The outside surface of the reaming shell is provided with inset diamonds or other cutting media set to a diameter to cut a specific clearance for the core barrel. See also: reamer; reamer shell. Syn: reaming ring.

b. Sets of two or more shells that are alternated every 50 ft (15.24 m) to keep loss in gauge to the hole uniform. The shell is changed when wear reaches 0.012 in (0.03 cm) below the original set diameter.

rebar
 * See: reinforcing bar.

recalescence
 * A phenomenon, associated with the transformation of gamma iron to alpha iron on the cooling (supercooling) of iron or steel, revealed by the brightening (reglowing) of the metal surface owing to the sudden increase in temperature caused by fast liberation of the latent heat of transformation. Syn: point of recalescence.

recarburize
 * a. To increase the carbon content of molten cast iron or steel by adding carbonaceous material, high-carbon pig iron, or a high-carbon alloy.

b. To carburize a metal part to return surface carbon lost in processing.

recarburizing
 * Introducing spiegeleisen into the converter after the blow to add the desired element.

recast
 * To form anew by running, as molten metal, into a mold; cast again; as, to recast a cracked bell.

receiving hopper
 * A hopper used to receive and direct material to a conveyor.

Recent
 * The later of the two geologic epochs comprised in the Quaternary period, in the classification generally used; Holocene. Also, the deposits formed during that epoch. Recent includes the geologic time and deposits from the close of the Pleistocene (glacial) epoch until and including the present.

receptor
 * See: acceptor.

recession
 * Going back, as the gradual retreat of a waterfall or an erosional escarpment, the melting back of a glacier, or the withdrawal of a body of water so that the shoreline moves successively farther away from the higher land.

recharge
 * a. The processes by which water is absorbed and added to the zone of saturation, either directly into an aquifer or indirectly by way of another formation; also, the quantity of water so added.

b. Putting water brought from elsewhere into a body of ground water to augment ground-water supply. See also: intake area.

reciprocal lattice
 * An array of points, each point at a distance that is the reciprocal of the d spacing between planes in the direction normal to each set of parallel planes as measured from the origin. Each reciprocal-lattice point may be associated with Bragg diffraction in a crystal. CF: crystal lattice; direct lattice; X-ray diffraction.

reciprocal strain ellipsoid
 * In elastic theory, an ellipsoid of certain shape and orientation that under homogeneous strain is transformed into a sphere. CF: strain ellipsoid.

reciprocating
 * Having a straight back-and-forth or up-and-down motion.

reciprocating drill
 * A piston drill often referred to as a hammer drill.

reciprocating engine
 * Any steam or internal-combustion engine, which has a piston moving under pressure within a cylinder.

reciprocating feeder
 * a. A feeder in which the material is carried on a plate subjected to a reciprocating motion and so constructed that when the plate moves in the reverse direction the material remains stationary. The rate of feed is normally varied by adjusting the stroke of the reciprocating plate. See also: plate feeder.

b. A device used to empty a bin or hopper from the bottom by horizontal reciprocating action of its parts, usually after primary crushing.

reciprocating flight conveyor
 * A reciprocating beam or beams with hinged flights arranged to advance bulk material along a conveyor trough. See also: grit collector.

reciprocating pump
 * A pump consisting of a piston or plunger which lifts water to a higher level by a series of to-and-fro movements. See also: pump.

reciprocating screen dryer
 * Usually an inclined reciprocating screen on which the coal travels and through which the hot gases pass. The screen may eliminate moisture in coal up to 2-1/2 in (6.4 cm) in size. It may also serve as a fine coal dryer to treat coals down to 1/8 in (0.32 cm).

recirculating water
 * Circulating water that has been in the circuit for more than one cycle, often recovered from a collecting device such as a thickener from which the clarified water is circulated back into the process stream.

recirculation
 * The continuous circulation of all or some part of the same air in part of a mine ventilation system.

recirculation of air
 * A term describing a condition in which the ventilating air current is returned to the face repeatedly along a circuitous path. It may happen in the case of auxiliary fans or booster fans. If the intake end of the air pipes of a blowing fan is not placed well to the intake side of the main air current, the foul air from the heading may be recirculated to the face again and again. With an exhausting auxiliary fan, the end of the pipes is kept well to the return side of the main air current. See also: two-fan auxiliary ventilation.

recirculation of water
 * The water used in a condenser or in a washery or other wet process is often repumped into the system by means of a circulating pump. The practice is economical in water and in reagent consumption and also reduces pollution of local streams. Water that is recirculated is clarified to reasonable purity. See also: washery water.

reclaiming
 * a. Digging from stockpiles.

b. Reprocessing previously rejected material.

reclaiming conveyor
 * a. Any of several types of conveyors used to reclaim bulk materials from storage.

b. The conveyor which receives material from the reclaimer in a blending system.

reclamation
 * a. The recovery of coal or ore from a mine, or part of a mine, that has been abandoned because of fire, water, or other cause.

b. Restoration of mined land to original contour, use, or condition.

recleaner cell
 * See: cleaner cell.

reclosing circuit breaker
 * A circuit breaker that recloses automatically as soon as the demand for current becomes equal to or less than that for which the circuit breaker is set.

recommended exposure limit
 * An 8-h or 10-h time-weighted average or ceiling of exposure to coal dust concentration; recommended by NIOSH and based on an evaluation of the health effects data.

recomposed granite
 * a. An arkose consisting of consolidated feldspathic residue (produced by surface weathering of an underlying granitic rock) that has been so little reworked and so little decomposed that upon cementation the rock looks very much like the granite itself. It has a faint bedding, an unusual range of particle sizes (unlike the even-grained or porphyritic texture of true granite), and a greater percentage of quartz than is normal for granite. Syn: reconstructed granite.

b. A conglomerate that has been recrystallized by metamorphism into a rock that simulates granite, as in the Lake Superior region. CF: meta-arkose.

recomposed rock
 * A rock produced in place by the cementation of the fragmental products of surface weathering; e.g. a recomposed granite. The term has been applied to a rock of intermediate character straddling an unconformable surface between the breccia of the lower formation and the conglomeratic base of the upper formation.

reconnaissance
 * a. A general, exploratory examination or survey of the main features (or certain specific features) of a region, usually conducted as a preliminary to a more detailed survey; e.g. an engineering survey in preparing for triangulation of a region. It may be performed in the field or office, depending on the extent of information available.

b. A rapid geologic survey made to gain a broad, general knowledge of the geologic features of a region.

reconnaissance map
 * A map incorporating the information obtained in a reconnaissance survey and data obtained from other sources.

reconnaissance sampling
 * See: pilot sampling.

reconnoiter
 * To make a reconnaissance of; esp. to make a preliminary survey of an area for military or geologic purposes.

reconstructed amber
 * See: pressed amber.

reconstructed granite
 * See: recomposed granite.

reconstructed turquoise
 * An imitation turquoise made of finely powdered ivory which is deposited in a solution of copper.

reconstruction
 * The modernization of underground roadways, transport, ventilation systems, and the layout of mine workings. It may include modernization of shafts and winding and also the improvement of surface handling and cleaning or washing equipment. See also: mechanization.

reconstructive transformation
 * An isochemical change in a crystal structure in which chemical bonds are broken and reformed, e.g., tridymite-quartz or diamond-graphite. CF: dilational transformation; displacive transformation; rotational transformation; phase transformation.

record borehole
 * See: record hole.

record hole
 * The first borehole drilled in an area that is cored so that a detail record of the formations penetrated can be obtained. Also called test hole. See also: stratigraphic hole. Syn: record borehole.

recording gage
 * A gage which automatically records the level of water in a stream or tank, or velocity and pressure in a pipe. It is operated by a float or by a submerged air tank fitted with a rubber diaphragm.

record table
 * Heavy-duty shaking table used to treat relatively coarse sands. Shaking is by double-link eccentric motion, with longer and slower throw than with Wilfley type of table.

recover
 * a. To restore a mine or a part of a mine that has been damaged by explosion, fire, water, or other cause to a working condition.

b. See: recovery.

recoverable grade
 * The true mill-head grade of an ore-stream in percent, ounces, or parts per million of a metal or mineral, less extractive metallurgical losses; the proportion of an ore material actually recovered.

recovered sulfur
 * Elemental sulfur produced from hydrogen sulfide obtained from sour natural gas, petroleum refinery gas, water gas, and other fuel gases.

recovery
 * a. The percentage of valuable constituent derived from an ore, or of coal from a coal seam; a measure of mining or extraction efficiency.

b. The ratio of the footage of core acquired from core drilling a specific length of borehole, expressed in percent. c. The carat weight of diamonds salvaged from a worn bit.

recovery plant
 * a. A plant designed for separating diamond particles from concentrate by various processes, usually including grease belts, jigs, electrostatic separators, and flotation. Also known as picking station.

b. The processing facility where minerals are recovered.

recreational mining
 * Mining as an avocation rather than as a business.

recrystallization
 * The formation, essentially in the solid state, of new crystalline mineral grains in a rock. The new grains are generally larger than the original grains, and may have the same or a different mineralogical composition.

recrystallized silicon carbide
 * A refractory made of about 98% to 99% SiC.

rectangular drainage pattern
 * A drainage pattern in which the main streams and their tributaries display many right-angle bends and exhibit sections of approx. the same length; it is indicative of streams following prominent fault or joint systems that break the rocks into rectangular blocks.

rectangular shaft
 * A shaft excavated to an oblong shape. The majority of shafts sunk in the Republic of South Africa before 1948 were rectangular and timber lined. The shape lends itself to equipping concurrently with sinking; it provides a convenient in-line hoisting arrangement and can easily be divided into separate compartments. However, in the 1950's and 1960's developments were towards the concrete lined circular shaft. See also: compartment.

rectification
 * a. The process by which electric energy is transferred from an alternating-current circuit to a direct-current circuit.

b. The purification of a liquid by redistillation. c. In electronics and signal processing, the transformation of a signal from an alternating positive and negative signal into an all-positive signal by taking its absolute value.

rectifier
 * Equipment used in mines to convert alternating current to direct current.

rectifying device
 * An elementary device consisting of one anode and its cathode that has the characteristic of conducting current effectively in only one direction.

rectorite
 * A clay mineral with regularly interstratified mica and smectite layers. Syn: allevardite.

recumbent fold
 * An overturned fold, the axial surface of which is horizontal or nearly so.

recuperator
 * a. A continuous heat exchanger in which heat is conducted from the products of combustion to incoming air through flue walls.

b. A system of thin-walled refractory ducts used for the purpose of transferring heat from a heated gas to colder air or gas. c. Preheating equipment for recovering sensible heat from hot spent gases from a furnace and using it for heating incoming charge or fuel gases; essentially, a low-pressure heat exchanger. Syn: regenerative heating.

recurrence horizon
 * A layer of peat marking a sharp change in the character of the peat and resulting from a profound change in climate.

red antimony
 * See: kermesite.

red arsenic
 * See: realgar.

red beds
 * Sedimentary strata composed largely of sandstone, siltstone, and shale, with locally thin units of conglomerate, limestone, or marl, that are predominantly red in color due to the presence of ferric oxide (hematite) usually coating individual grains; e.g. the Permian and Triassic sedimentary rocks of western United States, and the Old Red Sandstone facies of the European Devonian.

red cake
 * The vanadium concentrate in a milling operation.

red chalk
 * Hematite mixed with clay.

red clay
 * A brown to red deep-sea deposit, which usually contains manganese nodules or a film of manganese. It is the finest divided clay suspension that is derived from the land and transported by ocean currents, accumulating far from land and at the greatest depths. It has a high proportion of volcanic material due to lesser dilution of this material owing to slowness of accumulation of the clay portion. The color is believed to be caused by oxidation. Syn: brown clay.

red cobalt
 * See: erythrite.

red copper ore
 * See: cuprite.

red copper oxide
 * See: cuprite.

redd
 * a. Eng. To clear away fallen stone or debris. Syn: rid.

b. Northumb. Overburden. CF: ridding. c. Scot. To scour through, take down, or rip.

redd bing
 * A pile of waste made of material brought direct from the mine, not waste from washery.

reddingite
 * An orthorhombic mineral, Mn (sub 3) (PO (sub 4) ) (sub 2) .3H (sub 2) O ; forms a series with phosphoferrite; pink; at Redding, CT.

reddle
 * Red ocher mixed with clay. Also spelled ruddle, raddle.

reddleman
 * A dealer in reddle or red chalk.

red dog
 * Material of a reddish color resulting from the combustion of coal shale and other mine waste in dumps on the surface.

reddsman
 * Scot. One who works at night cleaning up and repairing roadways, etc.

red earth
 * The characteristic soil of most tropical regions. It is leached, red, deep, and clayey.

red glassy copper ore
 * See: cuprite.

red-hard
 * A term applied to some varieties of tool steels that will retain their hardness even when operating at a red heat.

red heart
 * A harmless reddish core, sometimes found in fire clay refractories.

red hematite
 * A compact columnar variety of hematite with a brownish-red to iron-black color; so called to contrast it with limonite and turgite. Syn: ironstone clay. CF: brown hematite.

redingtonite
 * A monoclinic mineral, (Fe,Mg,Ni)(Cr,Al) (sub 2) (SO (sub 4) ) (sub 4) .22H (sub 2) O ; halotrichite group; forms reddish-purple fibrous masses.

Red I plate
 * See: selenite plate.

red iron froth
 * A variety of hematite.

red iron ore
 * See: hematite.

red iron vitriol
 * See: botryogen.

redistilled metal
 * Metal from which the impurities, usually zinc and mercury, have been eliminated by selective distillation.

red lead
 * See: minium.

red lead ore
 * See: crocoite.

redledgeite
 * A tetragonal mineral, BaTi (sub 6) Cr (sub 2) O (sub 16) .H (sub 2) O ; cryptomelane group. Formerly called chromrutile.

red lime mud
 * A red mud to which lime, caustic soda, or quebracho, has been added. The pH is usually 12.0 to 13.0.

red manganese
 * Any reddish manganese mineral, i.e., rhodonite and rhodochrosite. Also called red manganese ore.

red mercury
 * Alleged to be a compound of mercury and antimony, and described in the press to be an ingredient of explosives or nuclear weapons manufacture or possibly a descriptive term employed to mask illicit trading activity involving controlled substances.

red metal
 * a. A copper matte containing about 48% copper.

b. Any one of several alloys used in the manufacture of silverware.

red mud
 * a. A reddish-brown terrigenous deep-sea mud that accumulates on the sea floor in the neighborhood of deserts and off the mouths of great rivers; contains calcium carbonate up to 25%.

b. A clay-water-base drilling fluid containing sufficient amounts of caustic soda and tannates to give a pronounced red appearance. The pH is usually 10.0 to 13.0.

red ore
 * Hematite ore.

red orpiment
 * See: realgar.

red oxide of copper
 * See: cuprite.

red oxide of zinc
 * See: zincite.

redox potential
 * Oxidation-reduction potential.

redrill
 * To reopen a borehole by redrilling after it has been cemented, caved, or lost because of junk in the hole. Also called drill out, drilled out. CF: overlap.

red roast
 * In fluidization roasting, conversion of iron from sulfides to red oxide.

redruthite
 * Corn. Copper glance. See: chalcocite.

reds
 * High explosive; used in mines.

red schorl
 * See: elbaite; rubellite; rutile.

redsear
 * In ironworking, to break or crack when red-hot, as iron under the hammer.

red silver
 * A red silver sulfide; esp. pyrargyrite and proustite. Syn: red silver ore.

red silver ore
 * See: red silver. Also called pyrargyrite; proustite.

reduce
 * a. To lower the oxidation state by adding electrons to a chemical species.

b. In general, to treat metallurgically for the production of metal.

reduced iron
 * Free iron in a fine state of division obtained by reducing ferric oxide by heating it in a current of hydrogen. Also called iron by hydrogen, iron powder, and spongy iron.

reduced level
 * Height above specified datum level of a surveyed point.

reduced natural frequency
 * The natural frequency of vibration of a foundation at an average ground pressure of unity is the reduced natural frequency divided by the square root of the ground pressure. This relationship has been established by Tschebotarioff.

reducing agent
 * a. A material that adds hydrogen to an element or compound.

b. A material that adds an electron to an element or compound; i.e., decreases the positiveness of its valence.

reducing atmosphere
 * a. An atmosphere having a deficiency of oxygen.

b. An atmosphere of hydrogen or other substance that readily provides electrons. c. Space from which air has been displaced by hydrogen, carbon monoxide, or other reducing gas.

reducing flame
 * The blue part or inner cone of the flame produced by a blowpipe; characterized by an excess of hydrocarbon over oxygen so as to reduce mineral samples heated in it. See also: blowpiping. CF: oxidizing flame.

reducing furnace
 * from other substances by a nonoxidizing heat or flame; usually a shaft furnace. Syn: reduction furnace.

reducing roast
 * The reduction of metallic oxides, sulfides, or halides by heating in contact with carbon or other reducing agents.

reduction
 * a. Process of reducing a metal compound to the metal and separating it from the slag; sometimes applied to the smelting process.

b. A reaction taking place at the cathode in electrolysis through transfer of electrons to the species being reduced. c. A decrease in positive valence, or an increase in negative valence by the gaining of electrons. A metallic oxide loses oxygen through the action of reducing gas, reducing its valence. CF: oxidation.

reduction cell
 * A pot or tank in which either a water solution of a salt or a fused salt is reduced electrolytically to form free metals or other substances.

reduction factor
 * The factor relating the allowable stress on a long column with that on a short column in order to prevent buckling.

reduction furnace
 * See: reducing furnace.

reduction of area
 * a. The difference between the cross-sectional area of a tension specimen at the section of rupture before loading and after rupture, expressed as a percentage of the original area.

b. Percentage decrease in cross-sectional area of bar or wire after rolling or drawing.

reduction of levels
 * The calculation of reduced levels from the staff readings recorded in a field book.

reduction ratio
 * In crushing, the ratio of the size of the largest feed particle to the smallest distance between the roll faces. As used frequently in the field, it is the ratio of the smallest aperture passing all of the feed to that passing all of the product. Another basis of expression is the ratio of the average size of feed to the average size of product. See also: overall reduction ratio; primary breaker.

reduction roasting
 * Lowering of oxygen content of ore by heating in reducing atmosphere.

reduction smelting
 * A pyrometallurgical process that produces an impure liquid metal and a liquid slag by heating a mixture of ore, flux, and reducing agent (usually coke).

reduction to center
 * The offset of a side auxiliary telescope requires a correction to observed horizontal angles, and the offset of a top auxiliary telescope requires a correction to observed vertical angles. The process of computing the correct angle from the observed angle is called reduction to center.

reduzate
 * A sediment formed in a strongly reducing environment; e.g., coal, sedimentary sulfides, or sedimentary sulfur.

red vitriol
 * See: bieberite; rose vitriol.

Redwood number
 * Viscosity, defined as rate of flow of oil from a Redwood viscometer.

red zinc ore
 * See: zincite.

red zinc oxide
 * See: zincite.

reed
 * a. Scot. Rift, or direction of easiest splitting.

b. Weakness in a sedimentary rock parallel with the bedding. See also: cleat. c. A reed filled with powder to act as a fuse. See also: spire.

reedmergnerite
 * A triclinic mineral, NaBSi (sub 3) O (sub 8) ; feldspar group; occurs in small colorless prisms having wedge-shaped terminations; from oil wells in Duchesne County, UT.

reef
 * a. A ridgelike or moundlike structure, layered or massive, built by sedentary calcareous organisms, esp. corals, and consisting mostly of their remains; it is wave-resistant and stands above the surrounding sediment. Also, such a structure built in the geologic past and now enclosed in rock, commonly of differing lithology.

b. A narrow ridge or chain of rocks either at the water surface or too shallow to permit safe passage of a vessel. CF: bank. c. A provincial term for a metalliferous mineral deposit, esp. gold bearing quartz. See also: reefing.

reef cap
 * A deposit of fossil-reef material overlying or covering an island or mountain.

reef drive
 * Aust. A cutting through the bedrock in alluvial mining for the purpose of seeking other underground, gold-bearing gravel channels.

reefing
 * Working auriferous reefs or veins. See: reef.

reef knoll
 * See: bioherm.

reef limestone
 * A limestone consisting of the remains of active reef-building organisms, such as corals, sponges, and bryozoans, and of sediment-binding organic constituents, such as calcareous algae.

reef wash
 * Aust. Gold-bearing drift.

reel
 * A device used for hoisting that has largely been replaced by round ropes. A flat rope is used for the reel, which is wound on an overlapping spiral like a clock spring. The reel is like a conical drum that increases in diameter by the thickness of the rope at each turn. Reels are more suitable for hoisting from a single level than from different levels.

reel boy
 * In bituminous coal mining, one who works on an electric locomotive--power being transmitted through an electric cable wound around a reel on the locomotive--tending the cable to see that it is wound up and fed from the reel so that it will not pull or break from the point where electric current is supplied. Also called nipper.

reel locomotive
 * A trolley locomotive with a wire rope reel for drawing cars out of rooms. The rope end is pulled by a runner into the face of the room, attached to a car, and reeled out by the locomotive.

reenforcing bar
 * See: reinforcing bar.

Ree's torsion anemometer
 * Consists of a thin square aluminum vane centrally suspended from a horizontal wire mounted in a vertical frame. The velocity of the air current is obtained from the measurement of the torque that has to be applied to the wire to bring the vane back to its vertical position. The instrument is mounted on a tripod, and the arrangement is such that the torsion can be applied, at a point 2 ft (0.6 m) away from the vane, by means of a shaft and bevel gearing. The instrument has been used to measure low air velocities in mines down to about 10 ft/min (3 m/min) and up to 180 ft/min (55 m/min). Syn: torsion anemometer.

reeve
 * The orderly arrangement of a rope or cable on a system of pulleys or sheaves to assemble block-and-tackle equipment for handling heavy loads. Also called reeved.

reeving
 * Threading or placement of a working line.

reference axes
 * In structural petrology, three mutually perpendicular axes to which structural measurements are referred. a is the direction of tectonic transport, c is perpendicular to the plane along which differential movement takes place, and b lies in this plane but is perpendicular to a.

reference electrode
 * Hydrogen electrode used to determine electrode potentials of half-cells.

reference level
 * See: datum plane.

reference mark
 * A selected distant point from which the bearings to other points can be measured at a survey station.

reference plane
 * See: datum plane.

reference seismometer
 * In seismic prospecting, a detector placed to record successive shots under similar conditions, to permit overall time comparisons. Used in connection with the shooting of wells for velocity.

reference size
 * Separation size, designated size, or control size used to define analyses of the products of a sizing operation.

reference standard
 * Taken or laid down as a standard for measuring, reckoning, or constructing.

reference station
 * A station for which tidal constants have previously been determined and that is used as a standard for the comparison of simultaneous observations at a second station; also, a station for which independent daily predictions are given in the tide or current tables from which corresponding predictions are obtained for other stations by means of differences or factors.

referencing
 * The process of measuring the horizontal (or slope) distances and directions from a survey station to nearby landmarks, reference marks, and other permanent objects that can be used in the recovery or relocation of the station.

refikite
 * An orthorhombic mineral, C (sub 20) H (sub 32) O (sub 2) ; soft; white; in modern resins and lignite at Montorio, Abruzzes, Italy. Also spelled reficite.

refine
 * a. To free from impurities; to free from dross or alloy; to purify, as metals; to cleanse.

b. To treat cast iron in the refinery furnace so as to remove the silicon.

refined iron
 * Wrought iron made by puddling pig iron.

refinery
 * a. A facility in which relatively crude smelter products such as blister copper are refined and emerge as acceptably pure products.

b. An electrolytic or chemical facility producing pure metals.

refining
 * The purification of crude metallic products.

refining heat
 * A medium orange heat, about 655 degrees C, which imparts fineness of grain and toughness to steel that is raised to it and afterwards quenched.

refining temperature
 * A temperature, usually just higher than the transformation range, employed in the heat treatment of steel to refine the structure, particularly the grain size.

reflected-light microscope
 * A compound microscope in which plane-polarized light impinges upon a polished specimen, commonly opaque, the light being reflected back to the objective through a second polarizer, where mineral color and polarization colors are observed in the ocular. Syn: ore microscope. See also: optical constant; polished section; microscopy.

reflected-light microscopy
 * See: ore microscopy.

reflected wave
 * A (gaseous) pressure wave resulting from a direct wave striking an obstacle or an opposing surface and being reflected backwards.

reflection
 * a. The return of a wave incident upon a surface to its original medium. CF: refraction; diffraction; total reflection.

b. The bounding back of light or other rays as they strike a solid surface. Light incident on a polished planar surface reflects at an angle equal to the incident angle, the proportion of reflected light increasing with increasing refractive index; e.g., for normal incidence, 17% reflects from diamond (n=2.4), and 5% reflects from quartz (n=1.5). c. In seismic prospecting, the returned energy (in wave form) from a shot that has been reflected from a velocity discontinuity back to a detector; the indication on a record of reflected energy. d. Misnomer for X-ray diffraction peaks. Also spelled reflexion.

reflection goniometer
 * An instrument that measures angles between crystal faces by reflecting a beam of light from successive faces as the crystal is rotated. See also: contact goniometer. CF: two-circle goniometer.

reflection mechanism
 * A rule stating that rock breaks from the surface inward toward the explosive rather than from the explosive charge outward. Syn: blasting reflection mechanism.

reflection method
 * See: seismic reflection method.

reflection shooting
 * A type of seismic survey based on measurement of the travel times of waves that originate from an artificially produced disturbance and are reflected back at near-vertical incidence from subsurface boundaries separating media of different elastic-wave velocities. CF: refraction shooting.

reflection wave
 * A wave that is propagated backward through the burned gas as the result of an explosion wave being completely or partly arrested against the closed extremity, or in a constricted portion of its path, as in a tube, gallery, etc.

reflectivity
 * The ratio of radiant energy reflected by a body to that falling upon it.

refraction
 * The deflection of a ray of light or of an energy wave (such as a seismic wave) due to its passage from one medium to another of differing density, which changes its velocity. CF: reflection; diffraction.

refraction method
 * A seismic method of geophysical prospecting. See also: refraction shooting.

refraction shooting
 * a. The detonation of heavy charges of explosive in comparatively shallow holes or pits. The effects may be measured over a wide area. The firing creates the shock waves in the seismic method of prospecting.

b. A type of seismic survey based on the measurement of the travel times of seismic waves that have traveled nearly parallel to the surface of high-velocity layers, in order to map such layers. See also: isochrone lines. CF: reflection shooting.

refractive index
 * See: index of refraction; dispersion.

refractometer
 * a. A combustible gases detector. See also: interference methanometer.

b. An instrument for measuring indices of refraction of transparent substances, both liquid and solid. CF: Abbe refractometer.

refractoriness
 * The capacity of a material to resist high temperature. In the refractories industry, the pyrometric cone equivalent (PCE) is a comparative value used to determine the refractoriness of a material.

refractory
 * a. Said of an ore from which it is difficult or expensive to recover its valuable constituents.

b. Exceptionally resistant to heat. c. A nonmetallic material suitable for use in high-temperature applications.

refractory bonding mortars
 * High-temperature bonding mortars containing various materials and exhibiting various properties, but primarily intended for providing structural bond between refractory units in high-temperature industrial furnace construction.

refractory brick
 * a. A brick made from refractory material, such as fire clay, bauxite, diaspore, etc., used to withstand high temperatures. Refractory bricks are made in various sizes and shapes.

b. A brick used as a lining for the interior of fireboxes in furnaces and boilers. Refractory brick is constructed so that it can withstand very high temperatures, but it is not a very good insulator.

refractory clay
 * See: fireclay.

refractory lining
 * A lining that has high refractory qualities and is therefore suitable for furnace linings and boiler foundations. It is made from a good-quality refractory ore, clay, fireclay, or gannister.

refractory material
 * A material able to withstand high temperatures and, therefore, used in such applications as lining furnaces.

refractory ore
 * Ore difficult to treat for recovery of the valuable substances.

refractory stone
 * Consists of sandstone, quartzite, mica schist, soapstone, or other rock that will withstand a moderately high temperature without fusing, cracking, or disintegrating. It may be used in solid blocks or crushed and mixed with a binder to form bricks.

refractory ware
 * Usually hollow ware, such as, saggers, pyrometer tubes, crucibles, etc.; also refractory brick and shapes.

refresher training
 * In mining, training given to all miners at least once a year consisting of 8 hours of instruction reviewing the essentials of new miner training. CF: new miner training; task training.

refrigerant
 * A substance that will absorb heat while vaporizing and whose boiling point and other properties make it useful as a medium for refrigeration.

refrigeration
 * a. In special application to mining, cooling of air before release in lowest levels of deep, hot mine; also, expansion of compressed air for the same purpose.

b. The process of absorption of heat from one location and its transfer to and rejection at another place; arbitrarily expressed in units of (short) tons and is equal to the coil cooling load divided by 12,000; 1 st (0.9 t) of ice in melting in 24 h liberates heat at the rate of 200 Btu/min (211 kJ/min), or 12,000 Btu/h (1.27 MJ/h).

refrigeration plant
 * a. A surface plant to form the protective barrier of frozen ground in the freezing method of shaft sinking. The cooling agent used is ammonia which, in its gaseous state, is compressed to about 120 psi (827 kPa) when it passes to the top of the condensers, emerging at the bottom as liquid ammonia under pressure. It then passes through a regulator valve into the coolers where it immediately evaporates. The latent heat of evaporation is extracted from the brine circuit--the brine being passed through the coolers by the brine pumps. The ammonia gas passes back for re-use. The brine emerges from the coolers at a temperature of -4 degrees F (-21.7 degrees C) and is pumped down the boreholes to freeze the water around the shaft sinking.

b. A surface plant to cool liquids. These liquids or ice are sent underground to cool the air current in heat exchangers. By this method, the air in deep mines is cooled considerably and the working environment is improved. See also: deep mining.

refuge chamber
 * An airtight, fire-resistant room in a mine used as a refuge in emergencies by miners unable to reach the surface.

refuge hole
 * A place formed in the side of an underground haulageway in which a worker can take refuge during the passing of a train, or when shots are fired. Also called refuge stalls. See also: manhole.

refusal
 * A condition arrived at when driving pipe, casing, piling, etc., when it cannot be driven to a greater depth or made to penetrate the ground a distance of more than 1 ft (30.5 cm) per 100 blows delivered by a drive hammer.

refuse
 * a. Waste material in the raw coal that has been removed in a cleaning or preparation plant.

b. Notably used to describe colliery rejects; also called tailings.

refuse conveyor
 * An adaptation of a drag chain conveyor.

refuse discharge pipes
 * Pipes used on some washboxes instead of a refuse worm.

refuse elevator
 * See: reject elevator.

refuse extraction chamber
 * That part of the washbox into which the refuse extractor discharges.

refuse extractor
 * A device used in a washbox to remove the reject from the washing compartments, operated manually or automatically.

refuse rotor
 * A reject gate in the form of a rotary (or star) valve.

refuse worm
 * A screw conveyor fitted at the bottom of some washboxes to collect the fine reject which has passed through the apertures in the screen plate.

regalian doctrine
 * The old doctrine that all mineral wealth was the prerogative of the crown or the feudatory lord. The concession system, in which the state or the private owner has the right to grant concessions or leases to mine operators at discretion and subject to certain general restrictions, had its origin in this doctrine. Almost all mining countries of the world, except the United States, follow this system.

regal jade
 * See: Indian jade.

regenerated anhydrite
 * Anhydrite produced by dehydration of gypsum that itself was generated by the hydration of anhydrite.

regenerated dense medium
 * Medium obtained from the medium recovery system and purified (wholly or partly) from contaminating fine coal and clay.

regeneration
 * a. In mineral leaching, reconstitution of barren leach solution after it has completed its chemical attack on mineral and its values have been removed. The regeneration of ion exchange resins and activated carbons by the removal of elements or compounds from extraction sites on the resins by special eluants.

b. A reversing heat exchanger for preheating combustion air (and gaseous fuels) from waste heat of the exhaust gases.

regenerative chambers
 * Separate compartments connected with a furnace; they are arranged for preheating the gas and the air used for fuel.

regenerative furnace
 * A furnace in which hot gases, usually waste combustion gases, pass through a set of chambers containing firebrick structures, to which the sensible heat is given up. The direction of hot-gas flow is diverted periodically to another set of chambers and cold incoming combustion gas or air is preheated in the hot chambers.

regenerative heating
 * See: recuperator.

regenerative principle
 * Used in open-hearth furnaces to increase the furnace temperature by preheating the fuel gas and air previous to their combustion in the furnace.

regenerator checkers
 * Brick used in furnace regenerators to recover heat from hot outgoing gases, and later to release this heat to cold air or gas entering the furnace; so called because of the checkerboard pattern in which the bricks are arranged.

regime
 * In hydraulics, the condition of a river with respect to the rate of its flow as measured by the volume of water passing different cross sections in a given time.

regional
 * a. Extending over large areas in contradistinction to local or restricted areas.

b. In gravity prospecting, contributions to the observed anomalies due to density irregularities at much greater depths than those of the possible structures, the location of which was the purpose of the survey. The term is also employed in an analogous sense in magnetic prospecting.

regional anomaly
 * a. The more localized departures in the Earth's field from the values that would be predicted if the field were to originate with a single magnet oriented along the magnetic axis. These have maximums as great as 10,000 gamma, which is about a third the total intensity at the equator, and extend over areas as large as a million square miles. The locations of such features do not change with time as do anomalies associated with secular variation.

b. The departure of a measured quantity from an expected or theoretical value on a scale larger than the most rapid spatial variations of the measured quantity; typically variations over tens to hundreds of kilometers.

regional dip
 * The nearly uniform inclination of strata over a wide area, generally at a low angle, as in the Atlantic and Gulf coastal plains and parts of the Midcontinent region. CF: homocline. Syn: normal dip.

regional metamorphism
 * A general term for metamorphism affecting an extensive region, as opposed to local or contact metamorphism. CF: dynamothermal metamorphism; local metamorphism.

regional unconformity
 * A surface of discontinuity in sedimentary rocks that extends throughout an extensive region. It may record a significant interruption in deposition, tectonics, or erosion of older strata.

registered premises
 * Premises registered with the local authority for the storage of not more than 60 lb (27.2 kg) of explosive. See also: licensed store; magazine.

reglette
 * A 12-in (0.3-m) scale divided into tenths and hundredths of a foot, used for accurate measurement in conjunction with a steel band that is graduated only in feet. See also: band chain.

regolith
 * The layer or mantle of loose incoherent rock material, of whatever origin, that nearly everywhere underlies the surface of the land and rests on bedrock. It comprises rock waste of all sorts: volcanic ash, glacial drift, alluvium, windblown deposits, organic accumulations, and soils. Syn: mantle rock.

regular lay
 * Wire rope or cable in which the individual wire or fibers forming a strand are twisted in a direction opposite to the twist of the strands. Also called ordinary lay. Syn: standard lay.

regular-lay left lay
 * See: left regular lay.

regular-lay right lay
 * See: right regular lay.

regular polygon
 * A polygon having equal sides, and the angles between these sides are equal.

regular sampling
 * The sampling of the same coal or coke received regularly at a given point. There are two forms of regular sampling, namely, continuous sampling and intermittent sampling.

regular ventilating circuit
 * All places in a mine through which there is a positive flow of air without the aid of a blower fan or of ventilation tubing.

regulated feed
 * In contrast with choke feed, feed that is throttled back to a value below the full capacity of the crusher.

regulated split
 * In mine ventilation, a split where it is necessary to control the volumes in certain low-resistance splits to cause air to flow into the splits of high resistance.

regulating gate
 * A gate used to vary size of opening so as to control the flow of material through the opening. See also: bin gate.

regulator
 * a. A ventilating device, such as an opening in a wall or door; usually placed at the return of a split of air to govern the amount of air entering that portion of a mine.

b. A device for creating shock loss to restrict passage of air through an airway. Regulators are usually set in doors as adjustable, sliding partitions that can be varied to the desired opening. In their simplest form, for temporary service in an untraveled part of a mine, regulators consist of doors propped partially open. Where possible, regulators are located on the exhaust side of a split (in a return airway) to minimize interference with traffic. See also: ventilation. Syn: ventilation regulator.

regulator door
 * See: scale door.

regulus
 * Impure metal produced during smelting of ores or concentrates.

reheater
 * An apparatus for reheating a substance, as ingot steel, that has cooled or partly cooled during some process.

reheater load
 * The amount of sensible heat in w (British thermal units per hour), restored to the air in reheating.

reheating furnace
 * The furnace in which metal ingots, billets, blooms, etc., are heated to bring them to the temperature required for hot-working.

Rehisshakenhobel
 * A plow developed from the Anbauhobel machine and designed for cutting thin coal seams. The plow drives, instead of being on the face side of the conveyor, are on the waste side and the plow chains run in two tubes along the waste side of the conveyor chutes. See also: Anbauhobel.

reinerite
 * An orthorhombic mineral, Zn (sub 3) (AsO (sub 3) ) (sub 2) ; blue to green; at Tsumeb, Namibia. (Not renierite.)

reinforcing bar
 * a. The basic material used to form grouted roof belts.

b. Iron or steel bars of various cross-sectional shapes used to strengthen concrete. c. See: rebar; reenforcing bar.

reinforcing steel
 * Steel bars of various shapes used in concrete construction to give added strength.

reinite
 * A pseudomorph, FeWO (sub 4) ; after scheelite(?).

reiteration
 * In surveying, angular measurement made first with vertical circle of theodolite to right of sighting telescope, then repeated after transiting this through 180 degrees . Also called face right, face left observation.

reject
 * a. The material extracted from the feed during cleaning for retreatment or discard.

b. The stone or dirt discarded from a coal preparation plant, washery, or other process; has no value. See also: middlings; refuse; residue; tailings.

reject elevator
 * An elevator for removing and draining the reject from a washing appliance. Syn: refuse elevator.

reject gate
 * The mechanism of the refuse extractor that may be manually or automatically operated to control the rate of removal of reject from the washbox.

rejuvenation
 * The renewal of any geologic process, such as the revival of a stream's erosive activity or the reactivation of a fissure.

relative age
 * The geologic age of a fossil organism, rock, geologic feature, or event, defined relative to other organisms, rocks, features, or events rather than in terms of years. CF: absolute age.

relative biological effectiveness
 * The relative effectiveness of a given kind of ionizing radiation in producing a biological response as compared with 250,000 electron-volt gamma rays. Abbrev., rbe.

relative bulk strength
 * A measure of the energy available per unit volume of explosive as compared to an equal volume of ANFO at a density of 0.81 g/cm (super 3) ; it is calculated by dividing the bulk strength of an explosive by the bulk strength of ANFO and multiplying by 100. See also: absolute bulk strength.

relative compaction
 * a. For soil compaction, two types of tests are necessary: (1) determining the dry density of the soil after a standard amount of compaction has been applied, and (2) measuring the density of the soil in the field. The state of compaction is expressed as the relative compaction, and is the percentage ratio of the field density to the maximum density as determined by standard compaction. The percentages of relative compaction are high, since the initial relative compaction is about 80%.

b. The dry density of a soil in situ divided by the maximum dry density of the soil as established by the Proctor compaction test or any other standard test. See also: loose ground.

relative consistency
 * The ratio of the liquid limit minus the natural water content to the plasticity index.

relative density
 * a. The relative density or specific gravity of a substance denotes the number of times the substance is heavier or lighter than water (for the same volume). Relative density and specific gravity mean the same thing.

b. The ratio of the difference between the void ratio of a cohesionless soil in the loosest state and any given void ratio to the difference between its void ratios in the loosest and in the densest states.

relative humidity
 * The ratio, expressed as a percentage, of the amount of water vapor in a given volume of air to the amount that would be present if the air were saturated at the same temperature. CF: absolute humidity; specific humidity.

relative movement
 * In fault descriptions, the displacement of one block relative to the other, rather than to some fixed point or plane of reference.

relative roughness
 * The dimensionless ratio Epsilon /d (where Epsilon is the average height of the surface irregularities and d is the diameter of the pipe) is termed the relative roughness. The physical interpretation of this functional equation is that the friction factors of pipes are the same if their flow patterns in every detail are geometrically and dynamically similar. The term Epsilon indicates the height of the irregularity above the boundary surface only; hence it is apparent that, dependent upon the thickness of the boundary layer adjacent to the surface, the projection can either lie submerged within the boundary layer or else project outside it.

relative time
 * Geologic time determined by the placing of events in a chronologic order of occurrence; esp., time as determined by organic evolution or superposition. CF: absolute time.

relative variogram
 * A variogram in which the ordinary variogram value for each lag has been divided by the square of the mean of the sample values used in computing the lag. This is sometimes useful when a "proportional effect" is present; i.e., when areas of higher than average concentration also have higher than average variance. When relative variogram models are used in kriging, the resulting kriging standard deviations represent decimal fractions of the estimated values.

relative weight strength
 * This is a measure of the energy available per weight of explosive as compared to an equal weight of ANFO. It is calculated by dividing the absolute weight strength (AWS) of the explosive by the AWS of ANFO and multiplying by 100. See also: absolute weight strength.

relaxation
 * a. In experimental structural geology, the release of applied stress with time, due to any of various creep processes.

b. In an elastic medium, the decrease of elastic restoring force under applied stress, resulting in permanent deformation. c. Relief of stress by creep. Some types of tests are designed to provide diminution of stress by relaxation at constant strain, as frequently occurs in service. d. The decrease of load support and of internal stress because of plastic strain at constant deformation.

relay
 * A device, operated by an electric current, and causing by its operation abrupt changes in an electrical circuit (making or breaking the circuit, changing of the circuit connections, or variation in the circuit characteristics).

relay haulage
 * Single-track, high-speed mine haulage from one relay station to another. Each operator has an exclusive track section between relay stations and can run at full speed since no other haulage equipment is operating on the section. Side track at each relay station permits the operator to pick up or drop off loads or empties, then make the return run. Also called intermediate haulage. See also: haulage.

relay motorman
 * See: gathering motorman.

release analysis
 * A procedure employed to determine the best results possible in cleaning a coal by froth flotation.

released mineral
 * A mineral formed during the crystallization of a magma as a consequence of an earlier phase failing to react with the liquid. Thus the failure of earlier formed olivine to react with the liquid portion of a magma to form pyroxene may result in the enrichment of the liquid in silica, which finally crystallizes as quartz, the released mineral.

release fracture
 * A fracture developed as a consequence of the relief of stress in one particular direction. The term is generally applied to a fracture formed when the maximum principal stress decreases sufficiently that it becomes the minimum principal stress; the fracture is an extension fracture oriented perpendicular to the then-minimum principal-stress direction.

release mesh
 * a. In liberation of specific mineral from its ore by comminution, the optimum grind.

b. Specified mesh-of-grind for best conditions for treatment to recover a specific mineral from the ore.

reliability of method
 * In geochemical prospecting, refers to the probability of obtaining and recognizing indications of an orebody or mineralized district by the method being used. Reliability depends not only on whether a readily detectable target exists and how effective the exploration method is in locating it, but also on the extent to which the anomaly is specif. related to ore and the extent to which it is possible that non-significant anomalies may confuse the interpretation.

relic
 * A landform that has survived decay or disintegration, such as an erosion remnant; or one that has been left behind after the disappearance of the greater part of its substance such as a remnant island. The term is sometimes used adjectivally as a synonym of relict, but this usage is not recommended.

relict
 * Pertaining to a mineral, structure, or feature of an earlier rock that has persisted in a later rock in spite of processes tending to destroy it. Also, such a mineral, structure, or other feature.

reliction
 * The slow and gradual withdrawal of the water in the sea, a lake, or a stream, leaving the former bottom as permanently exposed and uncovered dry land; it does not include seasonal fluctuations in water levels. Legally, the added land belongs to the owner of the adjacent land against which it abuts. Also, the land left uncovered by reliction.

relict texture
 * In mineral deposits, an original texture that remains after partial or total replacement.

relief
 * a. A term used loosely for the physical shape, configuration, or general unevenness of a part of the Earth's surface, considered with reference to variations of height and slope or to irregularities of the land surface; the elevations or differences in elevation, considered collectively, of a land surface. CF: topography.

b. The vertical difference in elevation between the hilltops or mountain summits and the lowlands or valleys of a given region. A region showing a great variation in elevation has high relief, and one showing little variation has low relief. c. The range of values over an anomaly or within an area; e.g., the gravity relief for the magnitude of a gravity anomaly. d. An apparently rough surface of a crystal section under a microscope. High relief indicates a great difference in index of refraction between the crystal and its mounting medium. The relief is positive if the refractive index of the mineral is greater than that of the medium, and negative in the reverse case. Syn: shagreen. e. The result of the removal of tool material behind or adjacent to the cutting edge to provide clearance and prevent rubbing (heel drag).

relief feature
 * See: landform.

relief holes
 * a. Boreholes that are loaded and fired for the purpose of relieving or removing part of the burden of the charge to be fired in the main blast.

b. Holes drilled closely along a line, that are not loaded, and that serve to weaken the rock so that it will break along that line. Syn: trim holes. c. Singular. A port or passageway through which the core, as it advances into the inner tube of a double-tube core barrel, forces water out of the inner tube to the outside of the barrel through the innertube head. d. Singular. A borehole drilled ahead of underground openings to tap and drain a water-bearing formation. Also called cover hole; pilot hole.

relief limonite
 * Indigenous limonite that is porous and cavernous in texture, commonly botryoidal after chalcocite. CF: indigenous limonite.

relief map
 * A map representing topographic relief of an area by contour lines, hachures, hill shading, coloring, or similar graphic means.

relief valve
 * A valve that will allow air or fluid to escape if its pressure becomes higher than the valve setting. Also called pressure relief valve.

relief well
 * A borehole that is drilled at the toe of an earth dam as a relief for any high water pressure caused by the weight of the dam.

relieving cut
 * In a round of shots planned for sequential firing when shaft sinking or tunneling, holes fired after cut holes and before lifters and slippers.

relieving platform
 * A loading deck for lorries on the land side of a retaining wall contructed, for example, as a jetty of steel sheet piling, the relieving platform being supported as a rule partly by the wall and partly by bearing piles. See also: surcharge.

relieving shot
 * A shot fired to dislodge or expose a misfire.

relighter flame safety lamp
 * A locked spirit-burning lamp fitted with an internal relighting device.

relighting station
 * A place in a mine at which safety lamps can be relighted under controlled conditions.

reluctance
 * Magnetic quality analogous to resistance in the flow of electric current.

remanence
 * Residual magnetism in a ferromagnetic substance (its hysteresis) after removal of an external magnetizing force.

remanent magnetization
 * a. Part of the magnetization of a body that does not disappear when the external magnetic field disappears.

b. That component of a rock's magnetization that has a fixed direction relative to the rock and is independent of moderate, applied magnetic fields such as the Earth's magnetic field. CF: induced magnetization. See also: hysteresis.

remnant
 * When a block of ground is stoped in such a way that at some time its remainder is surrounded on all sides by stoped ground, that remainder is termed a remnant.

remolded soil
 * Soil that has had its natural structure modified by manipulation.

remolding
 * Disturbance of the interval structure of clay or silt; when remolded, such material will lack shearing strength and gain compressibility. In consequence, driven piles are not recommended in certain clays. See also: thixotropic fluid.

remolding index
 * The ratio of the modulus of deformation of a soil in the undisturbed state to the modulus of deformation of the soil in the remolded state.

remolding sensitivity
 * The ratio of the unconfined compressive strength of an undisturbed specimen of soil to the unconfined compressive strength of a specimen of the same soil after remolding at unaltered water content. Also called sensitivity ratio.

remolinite
 * See: atacamite.

remote control
 * a. The control of plant operation by personnel or computers housed under conditions that can be remote, safe, and convenient. This is a feature of both electrical and electronic automatic control. In the control room, various plants can be started up by pushbutton and the governing conditions can be set. Instrumentation records all relevant data; it also gives warning of unsafe conditions and shuts down the plant if no correction is made. Changeover switches can introduce different operations and sequences in the working of the plant. Indicating lights can show what plant is working and the progress made. Fault indication can show the reason in the event of a shutdown. Also called centralized control.

b. A term applied to a switch, circuit breaker, starter, or similar apparatus, to denote that its operation can be controlled manually, from a distance, by electrical or other means.

remote control support system
 * A self-advancing support system in which the chocks and/or props are advanced and reset on a longwall face from a point in the gate road leading to the face. Hydraulic pressure and valves are commonly employed and the system is largely in the experimental stage. See also: pushbutton coal mining.

remote sensing
 * A branch of geophysics that acquires and interprets airborne or satellite images of the surface using infrared and visible wavelengths of light.

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