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Appendix:Dictionary of Mining, Mineral, and Related Terms/S/3

seabeach placers
 * Alaska. Placers adjacent to the seashore to which the waves have access.

sea bloom
 * See: plankton bloom.

sea coal
 * a. Old name for bituminous coal; so named either because it was exported by sea from collieries in coastal districts, or because it was at first applied to coal washed ashore from deposits below sea level.

b. Coal dug from the earth; so called formerly to distinguish it from charcoal, because it was brought to London by sea. Known formerly as pit coal or earth coal. c. U.S. Rare. Soft coal as distinguished from anthracite. d. Archaic. Mineral coal. e. Pulverized bituminous coal used as a foundry facing.

sea current
 * The currents that constitute part of the general oceanic circulation. Syn. for ocean current.

sea-floor trench
 * See: trench.

sea-foam
 * a. An early syn. for meerschaum.

b. See: sepiolite.

Seale construction
 * Wire strand construction having one size of wires for the outer layer with the same number of smaller wires in the underlayer. Both layers have the same length and direction of lay.

sealed area
 * In mining, portion of underground workings sealed off, usually because of fire (in which case no air is allowed to enter) or because no mineable coal remains in the area. See also: unsealing.

sealed-off area
 * A part of a mine that has been sealed off from the rest of the mine. The object of sealing off a fire area is to: (1) contain the trouble, and to prevent an explosion that may occur inby from extending to other parts of the mine; (2) build up an extinctive atmosphere inside the sealed-off area; and (3) prevent the access of air to the inby side of the seal.

Seale rope
 * A wire rope that has six or eight strands each, having a large center wire covered by nine small wires that are covered in turn by nine large wires.

Seale's lay
 * A wire rope with the inner and outer layers consisting of the same number of wires, the outer being larger and lying in the grooves or valleys between the inner wires. Both layers are stranded or laid in one operation. Extra support is given to the outer wires by this method and the wires are in line contact throughout and there is no internal crosscutting of wires.

sea level correction
 * The deduction made from a measured length of a base line to establish its true length at sea level. See also: tape corrections.

sealing
 * a. Shutting off all air from a mine or portion of a mine, a practice used in an emergency to check fire by eliminating oxygen. Also, as a routine shutting-off method for worked-out areas in some mines.

b. Sealing is used to overcome mine fires when other methods have failed. It involves the erection of temporary or permanent seals for the purpose of cutting off the oxygen supply to the area on fire. Sealing causes the fire to extinguish itself by consuming the oxygen in the sealed off area. c. Cutting off the air supply to effect extinction of underground fires by erecting sandbag stoppings at convenient places. The combustion process uses up the available oxygen within the sealed area, the process is arrested and the hot ground cools down gradually as the heat is conducted away by the surrounding cooler strata. See also: fire seal. d. Closing pores in anodic coatings to render them less absorbent. e. Plugging leaks in a casting by introducing thermosetting plastics into porous areas and subsequently setting the plastice with heat.

sealing-wax wood
 * Pieces of wood full of resin found in brown coal. When ignited they burn, melting and giving off soot and an aromatic odor like sealing wax.

seal off
 * The use of a cement or other sealant in a borehole. Seal off is not synonymous with blankoff and case off, where securing the walls of a borehole is accomplished by setting pipe or casing. CF: blankoff; seal.

seam
 * a. A stratum or bed of coal or other mineral; generally applied to large deposits of coal.

b. A particular bed or vein in a series of beds; it is usually said of coal but may also pertain to ore minerals. c. A thin layer or stratum of rock separating two distinctive layers of different composition or greater magnitude. d. A joint, cleft, or fissure. Syn: crevice. e. A plane in a coalbed at which the different layers of coal are easily separated. f. A very narrow vein. g. See: joint line.

seamanite
 * An orthorhombic mineral, Mn (sub 3) (PO (sub 4) )B(OH) (sub 6) ; pale- to wine-yellow; in the Chicagoan Mine, near Iron River, MI.

seam contour
 * A line drawn on a plan joining points on the floor or roof of a seam that have the same height above a prescribed datum.

seamount
 * An elevation of the sea floor, 1000 m or higher, either flat-topped (called a guyot) or peaked (called a seapeak). Seamounts may be either discrete, arranged in a linear or random grouping, or connected at their bases and aligned along a ridge or rise.

seam-out
 * A shot that merely blows out a soft stratum in the coal or escapes through a seam without loosening the main mass of coal. In Arkansas, called squeal-out.

seamy
 * Full of seams, so as to be difficult to blast.

search coil
 * a. Sensitive device, using the mine-detector principle, for locating ferromagnetic material that is to be removed before ore treatment. It typically monitors a stream of ore passing along a conveyor belt, which it stops when iron is detected.

b. Coil that is used in electromagnetic methods for measuring the magnetic field that is associated with the electric current.

search neighborhood
 * Any area searched during interpolation between sample data points. Applies to any interpolation method where a limited number of sample data points are used to estimate intermediate values.

searlesite
 * A monoclinic mineral, NaBSi (sub 2) O (sub 5) (OH) (sub 2) ; forms minute spherulites composed of radiating fibers; at Searles Lake, CA.

Searles Lake brine
 * A source of trona, Na (sub 3) (CO (sub 3) )(HCO (sub 3) ).2H (sub 2) O . Occurs in Searles Lake, San Bernardino County, CA.

sea sand
 * Sand containing alkaline salts that attract and retain moisture and cause efflorescence in brick masonry.

sea slick
 * An area of sea surface, variable in size and markedly different in appearance, with color and/or oiliness; usually caused by plankton blooms.

seasoned
 * Applied to quarrystone after the moisture has dried out.

seasoning
 * A mode of treatment of iron castings that are allowed to remain in storage, or to stand out in the open, for a more or less extended period, e.g., 6 months, to effect a reduction in the residual stresses and consequently in the degree of distortion during subsequent machining. A very similar result can often be obtained by a comparatively short period, e.g., 30 min, of tumbling. Since stress relieving by heat treatment is a more certain process, and seasoning involves much delay and the use of considerable space for storage, stress relieving is more usually employed.

seasoning timber
 * The drying of the sap and moisture in the woody fibers and thus reducing the timber by shrinkage. It becomes more durable and weighs less. Timber may be air-dried, i.e., dried naturally in air, or kiln-dried, which means dried in kilns under the action of artificial heat. The former is more general. See also: timber preservation.

sea state
 * Numerical or written description of ocean surface roughness.

seat
 * a. The underclay or fireclay on which a coal seam rests. Also called seating.

b. The foundation or framework on which a structure rests; e.g., engine seat, cage seat.

seat clay
 * See: underclay.

seat earth
 * a. A British term for a bed of rock underlying a coal seam, representing an old soil that supported the vegetation from which the coal was formed; specif. underclay. A highly siliceous seat earth is known locally as ganister. Also spelled: seatearth. Syn: seat rock; seat stone; hard seat.

b. A bed representing oil soil, usually containing abundant rootlets, underlying a coal seam. c. The soil on which the coal forests fluorished. d. Stratum underlying the valuable seam. Floor of a coal seam. See also: underlying; underclay.

seated
 * a. Placed in position.

b. Closed by pressing the closure part of a valve against its seat.

seating
 * The surface of the point of support for a heavy load.

seat of settlement
 * The deposit of soil under a loaded foundation within which the major settlement occurs. See also: excavation deformation; settlement.

seat rock
 * See: seat earth.

seat stone
 * See: seat earth.

sebkainite
 * Crude potassium chloride obtained by solar evaporation of brine from a lake south of Gabes, Tunisia.

sebkha
 * See: sabkha.

secant modulus of elasticity
 * Materials such as concrete or prestressing wire have a variable Young's modulus (E) so that the particular value of E adopted must be either the slope of the tangent to the stress-strain curve or that of the secant. The latter is the line that joins the origin of the curve to, for instance, the 0.1% proof stress, expressed on the curve. For a material within its elastic range, the secant will coincide with the tangent. See also: modulus of elasticity.

secondarily enriched deposit
 * Deposits that result from supergene enrichment.

Secondary
 * A term applied in the early 19th century as a syn. of Floetz. It was later applied to the extensive series of stratified rocks separating the older Primary and the younger Tertiary rocks, and ranging from the Silurian to the Cretaceous; still later, it was restricted to the whole of the Mesozoic Era. The term was abandoned in the late 19th century in favor of Mesozoic.

secondary
 * Said of metal obtained from scrap rather than from ore.

secondary air
 * In a combustion chamber, air that meets with primary air to consume the fuel completely and complete combustion.

secondary anomaly
 * See: geochemical anomaly.

secondary ash
 * Ash in coal derived from mineral matter precipitated in cleat clavities, etc. See also: extraneous ash.

secondary beam
 * A beam supported off, and transferring loads to, main beams that are themselves carried directly by the walls or columns.

secondary blasting
 * Irrespective of the method of primary blasting employed, it may be necessary to reblast a proportion of the rock on the quarry floor so as to reduce it to a size suitable for handling by the excavators and crushers available. Two methods of secondary blasting of rock are available. The first, called the plaster or mudcap method, is to fire a charge of explosive placed on the rock and covered with clay, the shock of the detonating explosive breaking the block. The second technique, known as pop-shooting, is to drill a hole into the block and fire a small charge in this hole, which is usually stemmed with quarry fines. Also called blistering; bulldozing. See also: plaster shooting; popping; snakeholing; pop shot; boulder blasting.

secondary cell
 * A group of flotation cells in which a product from the primary cells is retreated.

secondary clay
 * A clay that has been transported from its place of formation and redeposited elsewhere. CF: residual clay; primary clay. See: sedimentary clay.

secondary consolidation
 * Consolidation of sedimentary material, at essentially constant pressure, resulting from internal processes such as recrystallization.

secondary creep
 * Deformation of a material under a constant differential stress, with the strain-time relationship as a constant. CF: primary creep. Syn: steady-state creep.

secondary crusher
 * Crushing and pulverizing machines next in line after the primary crushing to further reduce the particle size of shale or other rock. See also: primary crusher. This group of machines includes the finer types of jaw crusher and gyratory crusher, and also crushing rolls, hammer mills, and edge runner mills.

secondary crushing
 * In ore dressing, the second stage of grinding in which the discharge from the primary crusher is broken down to a size suitable for feed to fine grinding machines.

secondary deposit
 * a. Made when the sediments already deposited are eroded and redeposited.

b. A mineral deposit formed when a primary mineral deposit is subjected to chemical and/or mechanical alteration. Secondary deposits are divided into three groups: sedimentary rocks, secondarily enriched ore deposits, and residual or detrital ore deposits.

secondary dispersion
 * Geochemical dispersion of elements by processes originating at the surface of the Earth; opposite of primary dispersion. Secondary patterns are those formed at the Earth's surface by weathering, erosion, or surface transportation. Secondary patterns have been classified more in detail as halos, fans, and trains, depending on the characteristic shape of the pattern and its geometric relationship to the ore deposit or other source.

secondary drilling
 * The process of drilling the so-called "popholes" for the purpose of breaking the larger masses of rock thrown down by the primary blast.

secondary dust source
 * If an operation agitates or disperses dust, it is a secondary source. See also: primary source.

secondary enlargement
 * Deposition, around a clastic mineral grain, of material of the same composition as that grain and in optical and crystallographic continuity with it, often resulting in crystal faces characteristic of the original mineral; e.g., the addition of a quartz overgrowth around a silica grain in sandstone.

secondary enrichment
 * See: supergene enrichment.

secondary environment
 * See: geochemical environment.

secondary fan
 * Any fan installed underground to ventilate tunnels or workings where the air current is sluggish. See also: mine ventilation auxiliary fan; booster fan.

secondary geochemical cycle
 * This cycle is comprised of the processes of weathering, soil formation, erosion, transportation, and sedimentation.

secondary grinding
 * Further comminution of material already reduced to sand sizes in rod or ball mills.

secondary hardness
 * Further increase in hardness produced on tempering high-speed steel after quenching due to precipitation of carbides.

secondary haulage
 * That portion of the haulage system that collects the coal from the various gathering-haulage delivery points and delivers it to the main haulage system.

secondary lead
 * Lead derived from salvage of wornout end-product items, such as battery plates, cable covering, pipe and sheet, which are collected, remelted, and refined in secondary smelters to produce refined lead or various lead-base alloys.

secondary metal
 * Metal recovered from scrap by remelting and refining.

secondary metal scrap
 * Metal recovered from scrap by remelting and refining.

secondary mineral
 * A mineral formed later than the rock enclosing it, usually at the expense of an earlier-formed primary mineral, as a result of weathering, metamorphism, or exsolution.

secondary mineral deposit
 * A mineral deposit formed when a primary mineral deposit is subjected to alterations through chemical and/or mechanical weathering. Secondary deposits are divided into three groups: sedimentary rocks, secondarily enriched mineral deposits, and residual or detrital mineral deposits.

secondary porosity
 * Porosity developed after the formation of a deposit and resulting from subsequent fracturing, replacement, solution, or weathering.

secondary products
 * See: middlings.

secondary reject elevator
 * A refuse elevator that extracts the second or lighter reject; usually situated at the discharge end of the washbox.

secondary rocks
 * Rocks composed of particles derived from the erosion or weathering of preexisting rocks, such as residual, chemical, or organic rocks formed of detrital, precipitated, or organically accumulated materials; specif., clastic sedimentary rocks.

secondary settling
 * a. The period following the primary settling in surface subsidence in which the surface subsides gradually. This period may continue for many years or even decades. CF: primary settling.

b. Residual subsidence.

secondary shaft
 * The shaft that extends a mine downwards from the bottom of the primary shaft but not in line with the primary shaft.

secondary shooting
 * In quarrying, the reduction in size or dimension of blasted rock by additional or secondary blasting.

secondary splits
 * The main air splits occur at the shaft bottom. In most cases, these splits are again separated at some point inby and these are called secondary splits. See also: ventilation; splitting.

secondary structure
 * A structure that originated after the deposition or emplacement of the rock in which it is found, such as a fault, fold, or joint produced by tectonic movement; esp. an epigenetic sedimentary structure, such as a concretion or nodule produced by chemical action, or a sedimentary dike formed by infilling. CF: primary structure.

secondary sulfide zone
 * See: sulfide zone.

secondary twinning
 * Twinning produced subsequent to the original formation of a crystal.

secondary vein
 * A vein discovered subsequent to the one on which a mining claim was based; an incidental vein. CF: discovery vein.

secondary water
 * Water entering the mine from other workings, as opposed to water inherent in the area worked by the mine.

secondary wave
 * See: S wave; transverse wave; distortional wave.

second-class lever
 * A lever whose force is exerted between the fulcrum and the point where it is applied.

second-class ore
 * An ore that needs preliminary treatment before it is of a sufficiently high grade to be acceptable for shipment or market. CF: first-class ore. Syn: milling ore.

second-foot
 * A unit of 1 ft (super 3) /s (0.0283 m (super 3) /s). Usually abbreviated to cusec.

second-foot-day
 * The volume of water represented by a flow of 1 ft (super 3) /s (0.0283 m (super 3) /s) for 24 hours. It is 86,400 ft (super 3) (2,445 m (super 3) ), or nearly 2 acre-feet (actually 1.9835); a convenient unit in storage computations.

second mining
 * a. The recovery of pillar coal after first-mining in chambers has been completed.

b. The recovery of pillars after development of block pillars by the multiple entry system has completed a panel.

second moment of area
 * The correct term for the moment of inertia (I) of the plane area of a section.

second or back explosion
 * Aust. Supposed to be due to the ignition of gases developed from highly heated coal dust, and gases sucked out of the faces of coal by the partial vacuum resulting from the primary explosion, or liberated by the fall of roof. CF: retonation wave.

second outlet
 * An emergency exit from a mine to the surface. Also called second opening; escapeway.

second ripping
 * The first back ripping on a roadway. See also: back brusher.

seconds
 * N.S.W. The second-class ore that requires dressing.

seconds A.P.I.
 * A unit of viscosity in drilling mud as measured with a Marsh funnel according to American Petroleum Institute procedure.

second weight
 * In mine subsidence, the powerful thrust or pressure, generally 20 to 40 ft (6 to 12 m) from the face, that causes distance from the roof to the floor to diminish rapidly and for packwalls to become compressed or pushed down into a soft bottom. Timber legs or metal supports (if any) in the gates are generally broken or twisted.

second worker
 * of years before being termed a first-class miner.

second working
 * a. The operation of getting or working out the coal pillars formed by the first working.

b. In coal mining, unless the pillars of coal are left permanently to support the surface, they are removed. This phase of mining is called the second working or pillar working. When the pillars are removed, nearly all of the coal has been recovered. CF: first working. Also called pillar working. See also: working the broken.

seconite
 * A finely ground plastic clay that in proportions not lower than 6% gives satisfactory green strength when used as a bond with molding sand.

secretion
 * a. The act or process by which animals and plants transform mineral material from solution into skeletal forms.

b. A secondary structure formed of material deposited from solution within a cavity in a rock, esp. a deposit formed on or parallel to the walls of the cavity; e.g., a mineral vein, an amygdule, or a geode. The space may be completely or only partly filled. CF: concretion.

sectile
 * a. Capable of being cut with a knife without breaking off in pieces.

b. Said of a mineral that can be cut with a knife; e.g., argentite. c. A physical property of minerals permitting shaving of curls with a knife; e.g., gypsum. CF: malleable.

sectility
 * A mineral is said to be sectile when it may be cut with a knife, but is not malleable, for example, graphite.

section
 * a. A portion of the working area of a mine.

b. Representation of features such as mine workings or geological features on a vertical (or inclined) plane. A longitudinal section is parallel to the strike of a vein or geologic plane. A cross section is perpendicular to the strike. c. Detailed measurement, taken vertically, of a coal vein or of strata embracing several veins. d. A drawing or diagram of the strata sunk through in a shaft or inclined plane, or proved by boring. e. The local series of beds constituting a group or formation. f. A piece of land that is 1 square mile (2.59 km (super 2) ) or 640 acres (259 ha) in area forming one of the 36 subdivisions of a township in a U.S. public-land survey.

sectionalizing circuit breaker
 * See: circuit breaker.

sectional mining belt conveyor
 * A belt conveyor so arranged that it can be lengthened or shortened by the addition or the removal of interchangeable increments or parts.

sectional tank
 * A water tank built up of standardized pressed steel units having external flanges that are bolted together in an assembly for varying sizes of tank.

sectional-type conveyor
 * A conveyor that is lengthened or shortened by adding or removing intermediate sections.

section boss
 * A more or less loosely used term applied to the assistant mine foreman in charge of an area, although used in law in some states in lieu of assistant foreman and certified as such.

section factor
 * See: section modulus.

section foreman
 * In anthracite and bituminous coal mining, a foreman who has complete charge of a section of a mine. Syn: section man.

section-gage log
 * See: caliper log.

section man
 * See: section foreman.

section modulus
 * The term pertains to the cross section of a beam. The section modulus with respect to either principal central axis is the moment of inertia with respect to that axis divided by the distance from that axis to the most remote point of the section. The section modulus largely determines the flexural strength of a beam of given material. Also called section factor.

section of rectifier unit
 * A part of a rectifier unit with its auxiliaries that may be operated independently.

sector gate
 * A roller gate in which the roller is in the form of a sector of a circle instead of being cylindrical.

secular
 * Said of a process or event lasting or persisting for an indefinitely long period of time, e.g., secular variation; progressive or cumulative rather than cyclic.

secular variation
 * A relatively large, slow change in part of the Earth's magnetic field caused by the internal state of the planet and having a form roughly to be expected from a simple, but not quite uniformly polarized sphere.

secundine dike
 * A dike that has been intruded into hot country rock. Pegmatites and aplites commonly occur in this mode.

sedentary
 * Formed in place, without transportation, by the disintegration of the underlying rock or by the accumulation of organic material; said of some soils, etc.

sediment
 * a. Solid fragmental material that originates from weathering of rocks and is transported or deposited by air, water, or ice, or that accumulates by other natural agents, such as chemical precipitation from solution or secretion by organisms, and that forms in layers on the Earth's surface at ordinary temperatures in a loose, unconsolidated form; e.g., sand, gravel, silt, mud, alluvium.

b. Strictly, solid material that has settled down from a state of suspension in a liquid. In the singular, the term is usually applied to material held in suspension in water or recently deposited from suspension. In the plural, the term is applied to all kinds of deposits, and refers to essentially unconsolidated materials. CF: deposit.

sedimentary
 * a. adj. Pertaining to or containing sediment; e.g., sedimentary deposit or a sedimentary complex.

b. Formed by the deposition of sediment (e.g., a sedimentary clay), or pertaining to the process of sedimentation (e.g., sedimentary volcanism).---n. A sedimentary rock or deposit.

sedimentary ash
 * a. Mineral matter introduced into the coal substance during its accumulation. See also: extraneous ash.

b. Ash in coal derived from the mud mixed up with plant debris during the formation of coal.

sedimentary clay
 * A clay that has been geologically transported from the site of its formation and redeposited elsewhere. The English ball clays, for example, are secondary kaolins. CF: primary clay. Syn: secondary clay.

sedimentary cycle
 * See: cycle of sedimentation.

sedimentary ore
 * A sedimentary rock of ore grade; an ore deposit formed by sedimentary processes, e.g., saline residues, phosphatic deposits, or iron ore of the Clinton ore type.

sedimentary petrography
 * The description and classification of sedimentary rocks. Syn: sedimentography.

sedimentary petrology
 * The study of the composition, characteristics, and origin of sediments and sedimentary rocks.

sedimentary rock
 * A rock resulting from the consolidation of loose sediment that has accumulated in layers; e.g., a clastic rock (such as conglomerate or tillite) consisting of mechanically formed fragments of older rock transported from its source and deposited in water or from air or ice; or a chemical rock (such as rock salt or gypsum) formed by precipitation from solution; or an organic rock (such as certain limestones) consisting of the remains or secretions of plants and animals. The term is restricted by some authors to include only those rocks consisting of mechanically derived sediment; others extend it to embrace all rocks other than purely igneous and completely metamorphic rocks, thereby including pyroclastic rocks composed of fragments blown from volcanoes and deposited on land or in water. Syn: stratified rock; derivative rock.

sedimentary rocks
 * Rocks formed by the accumulation of sediment in water (aqueous deposits) or from air (eolian deposits). The sediment may consist of rock fragments or particles of various sizes (conglomerate sandstone, shale); of the remains or products of animals or plants (certain limestones and coal); of the product of chemical action or of evaporation (salt, gypsum, etc.); or of mixtures of these materials. Some sedimentary deposits (tuffs) are composed of fragments blown from volcanoes and deposited on land or in water. A characteristic feature of sedimentary deposits is a layered structure known as bedding or stratification. Each layer is a bed or stratum. Sedimentary beds as deposited lie flat or nearly flat. See: stratified rocks.

sedimentary tuff
 * a. A tuff containing a subordinate amount of nonvolcanic detrital material.

b. A deposit of reworked tuff and other detrital material.

sedimentation
 * a. The act or process of settling particles by mechanical means from a state of suspension in air or water.

b. Method of classification by exploitation of free-falling rates of minute (subsieve) particles.

sedimentation balance
 * Apparatus used to measure settling rate of small particles dispersed in liquid. One scale-pan is immersed in the mixture, and the balance is adjusted by increasing the counterweight at suitable time intervals. Alternatively, a float is suspended, and the compensating external weight is reduced as the density of the suspension surrounding the float is reduced by settlement of its solids.

sedimentation test
 * A test used when selecting materials for stabilized road construction and concrete. Soil, after pretreatment, is shaken up in water and allowed to settle out. The change in specific gravity of the suspended matter with time is measured, and the equivalent diameter is calculated from Stokes' law. See also: organic test; Stokes' law.

sedimentation trend
 * The direction in which sediments were laid down. Uranium mineralization often follows such trends, owing to increased porosity, carbon precipitants, and other factors.

sedimentation unit
 * A layer or deposit formed under essentially constant physical conditions, distinguished from other units by differences in grain size and/or fabric, indicating changes in velocity and/or direction of flow.

sediment dispersion
 * The dilution and settling of sediment in a cloud as it advects from a point source.

sedimentography
 * See: sedimentary petrography.

sedimentology
 * The scientific study of sedimentary rocks and of the processes by which they were formed; the description, classification, origin, and interpretation of sediments.

sediment tube
 * A long open tube fixed above the core barrel in the shot-drill method of exploratory boring. The enlarged space above the sediment tube reduces the upward velocity of the flushing water and the coarse chippings are deposited in the tube where they are retained until drawn up to the surface. Also called calyx; sludge barrel.

sediment vein
 * A sedimentary dike formed by the filling of a fissure from above with sedimentary material.

Seebeck effect
 * The phenomenon involved in the operation of a thermocouple. Named for Thomas Seebeck, the German scientist, who first observed the phenomenon in 1822. See also: thermocouple.

seed charge
 * A small charge of material added to a supersaturated solution to initiate precipitation.

seed gypsum
 * Gypsum beds of loose small crystals.

seeding
 * In chemical treatment, addition of tiny crystals of material to a supersaturated solution to induce nuclear precipitation.

seepage line
 * See: line of seepage.

Seger cone
 * A small cone, made in the laboratory of a mixture of clay and salt, that softens at a definite, known temperature. It is used in the manufacture of refractories. It has also been used in volcanology to determine the approximate temperature of a molten lava. Syn: pyrometric cone.

segger
 * See: sagger.

segregate
 * a. Pac. To separate the undivided joint ownership of a mining claim into smaller individually segregated claims.

b. In geology, to separate from the general mass, and collect together or become concentrated at a particular place or in a certain region, such as in the process of crystallization or solidification. See also: segregated vein.

segregated vein
 * A fissure whose mineral filling is derived from the country rock by the action of percolating water. CF: infiltration vein. See also: lateral secretion.

segregation
 * a. A secondary feature formed as a result of chemical rearrangement of minor constituents within a sediment after its deposition; e.g., a nodule of iron sulfide, a concretion of calcium carbonate, or a geode.

b. Partial reseparation of a previously mixed batch of material into its constituents, as a result of differences in particle size or density. Segregation can occur in storage bins, on conveyors, and in feeders during dry or semidry processing.

segregation banding
 * A compositional banding in gneisses that is not primary in origin, but rather is the result of segregation of material from an originally more nearly homogeneous rock.

segregation survey
 * The survey of a mining claim located on lands classified as agricultural.

sehta
 * See: cobaltite.

seidozerite
 * A monoclinic mineral, Na (sub 4) MnTi(Zr (sub 1.5) Ti (sub 0.5) )O (sub 2) (F,OH)(Si (sub 2) O (sub 7) ) ; forms brown-red needles embedded in microcline in a nepheline syenite pegmatite; near Lake Seidozero, Lovozero massif, Kola Peninsula, Russia.

seif dune
 * A long, sharp-crested dune extending in the direction of the wind that constructed it.

S.E.I. photometer
 * In this instrument, the internal comparison lamp is set to a standard brightness as indicated by a photoelectric cell and not by reference to a voltmeter or ammeter.

seismic
 * a. Pertaining to, characteristic of, or produced by earthquakes or earth vibration; as, seismic disturbances; seismic records.

b. Pertaining to sound waves generated by earthquakes or artificially by explosives to map subsurface structure.

seismic activity
 * See: seismicity.

seismic analysis
 * A quick, easy, and inexpensive method of determining the consolidation of overburden. The process is based on the principle that sound or shock waves travel through different subsurface materials at varying speeds and along different paths. By this method the operator can determine whether overburden can be ripped or whether it will need to be drilled and blasted.

seismic area
 * The region affected by a particular earthquake.

seismic belt
 * a. One of the broad, more or less well-defined, elongate zones in which most earthquakes originate.

b. An elongate earthquake zone, esp. a zone of subduction or sea-floor spreading.

seismic detector
 * See: seismometer.

seismic diffraction
 * See: diffraction.

seismic drill
 * See: seismograph drill.

seismic event
 * Applied to any definite signal change or amplitude difference on a seismic record. It may be a reflection, a refraction, a diffraction, or a random signal.

seismic explosives
 * Special forms of blasting gelatin, or gelatin and ammonia gelatin dynamites, used in geophysical prospecting by the seismic method; developed to shoot consistently at their characteristic rate of detonation under unusually heavy water pressure.

seismic focus
 * The place of origin within the Earth of an earthquake; usually some more or less restricted area of a fault surface. If the focus is to be some particular point, it is the central point of the area over which fault movement occurred and caused the earthquake.

seismicity
 * a. Measure of frequency and magnitudes of earthquakes in a given area; e.g., the average number of earthquakes per year and per 100 km (super 2)

b. The phenomenon of earth movements.

seismic method
 * A geophysical prospecting method based on the fact that the speeds of transmission of shock waves through the Earth vary with the elastic constants and the densities of the rocks through which the waves pass. A seismic wave is initiated by firing an explosive charge (or by equivalent artificial sources) at a known point (the shot point); records are made of the travel times taken for selected seismic waves to arrive at sensitive recorders (geophones). There are two main subdivisions of seismic operations: the reflection method and the refraction method. The seismic method has been applied to a lesser extent to elucidate mining problems, partly due to its high cost. It has been used to investigate the base of drift deposits, and drift-filled channels have been successfully outlined.

seismic noise
 * See: microseism.

seismic prospecting
 * A method of geophysical prospecting in which vibrations are set up by firing small explosive charges in the ground or by other artificial sources. Precise measurements of the resulting waves are taken, from which the nature and extent of underlying strata are revealed.

seismic reflection method
 * In this geophysical prospecting technique, the structure of subsurface formations is mapped by making use of the times required for a seismic wave (or pulse), generated in the Earth by a near-surface explosion of dynamite or by other artificial sources, to return to the surface after reflection from the formations themselves. The reflections are recorded by detecting instruments responsive to ground motion, which are laid along the ground near the site of generation of the seismic pulse. Variations in the reflection times from place to place on the surface usually indicate structural features in the rock below. Syn: reflection method.

seismic refraction method
 * In refraction shooting, the detecting instruments are laid down at a distance from the shothole that is large compared with the depth of the horizon to be mapped. The seismic waves travel large horizontal distances along distinct interfaces in the Earth, and the time required for travel gives information on the velocity and depth of certain subsurface formations.

seismic shooting
 * a. The initiation of seismic waves in the rocks by the firing of an explosive charge at a known point. The disturbance must be capable of accurate timing and must be such that, after traveling considerable distances through varying strata, it produces a sharply defined effect on the seismograph. These requirements may be supplied by the shock produced by detonating a charge of high explosive. The intensity of the shock and its effective range can be controlled by varying the quantity of explosive charge. See also: reflection shooting; refraction shooting.

b. A method of geophysical prospecting in which elastic waves are produced in the Earth by the firing of explosives or by other means. See also: reflection shooting; refraction shooting.

seismic shothole
 * A hole drilled for a seismic shot. It is usually a slim hole, although it has also been termed core hole. See also: slim hole; structure test hole.

seismic spread
 * See: seismometer spread.

seismic survey
 * An exploration technique utilizing the variation in the rate of propagation of shock waves in layered media. It is used primarily to delineate subsurface geologic structures of possible economic importance.

seismic waves
 * The Earth motion produced by a natural (earthquake) or synthetic disturbance on the surface or underground; utilized in the seismic method of geophysical exploration and for investigating the Earth's interior. Three types of waves are produced: (1) longitudinal or P waves; (2) traverse or S waves; and (3) surface or Raleigh and L waves. The speed of propagation is characteristic for each type of rock, depending largely on its compactness. In sandy clay, the speed of the P wave is about 4,000 ft/s (1.22 km/s); in sandstone, 10,000 ft/s (3.05 km/s); and in igneous rock up to 22,000 ft/s (6.71 km/s).

Seismitron
 * An instrument designed to check ground stability. It amplifies 2.5 million times, and can detect a rock movement as small as 0.000001 in (2.54 mu m). Receiving phones are placed in holes in the area being tested. Either earphones or automatic recording apparatus may be used for listening. A rate of 3 or more microseisms per second indicates probable collapse, and any rate over 25 or 30 per minute is considered dangerous. This instrument is also finding use above ground in checking highway cut slopes.

seismogram
 * The record of Earth motion made by a seismograph.

seismogram synthesis
 * a. This process produces an artificial reflection record from a continuous-velocity log or an electric log. With this system the log is converted from a depth scale to a time scale and is run through a scanning device that transforms the fluctuations on the log into electrical impulses that vary with time so as to simulate reflections. These impulses are passed through appropriate filters and are then recorded on an oscillograph in the same way as signals from a geophone.

b. The theoretically calculated ground motion that would be recorded for a given Earth structure and seismic source.

seismograph
 * a. An instrument that detects, magnifies, and records motions of the Earth, esp. those caused by earthquakes or explosions. The resulting record is a seismogram. CF: seismometer; geophone.

b. The instrument used to record the reception of the waves in the sound seismic method. It works on the general principle that its frame is shaken by the arrival of the waves, while a pendulum of high inertia, mounted in it, remains stationary. The relative movement of the frame and the pendulum is magnified by optical means in the seismograph and by electrical amplifiers in the geophone. The instrument can also detect and record earthquakes. See also: geophone; vibrograph.

seismograph drill
 * A rotary drill, pump, and hinged mast mounted as an integral drilling unit on a truck body and used primarily to drill vertical shallow holes in which explosives are placed and detonated to produce shock waves from the rock strata, which then are measured by seismic recording instruments. Also called jackknife rig; rotary shot drill; shothole drill. Syn: seismic drill.

seismograph rod
 * A collared, tapered, V-thread-coupling drill rod used on seismograph drills.

seismology
 * a. The science of earthquakes and attendant phenomena.

b. A geophysical science that is concerned with the study of earthquakes and measurement of the elastic properties of the Earth. c. The study of earthquakes, and of the structure of the Earth, by both natural and artificially generated seismic waves.

seismometer
 * An instrument that detects Earth motions. Syn: seismic detector. CF: geophone; hydrophone; seismograph.

seismometer spacing
 * Distance between successive seismometer positions.

seismometer spread
 * A set of seismometers, placed along a straight line, that record the same shot.

seismoscope
 * An instrument that merely indicates the occurrence of an earthquake. It is considered by some, however, to be the equivalent of a seismometer.

seize
 * a. To bind wire rope with soft wire, to prevent it from raveling when cut.

b. See: bind; freeze. c. To cohere or stick to an inadequately lubricated moving part, such as a bearing, piston, or sliding part, through excessive friction, pressure, or temperature. d. To protect rope ends by binding with yarn, marline, or fine wire.

selected fill
 * Dumped fills made up of selected materials. These fills are used when it is desired to utilize a particular property of a soil or rock and this property can be secured solely by selective excavation.

selective agglomeration
 * In coal beneficiation, the separation of coal from associated impurities, usually aided by additions of oily reagents that selectively attach to the coal surfaces. Generally restricted to material of 500 mu m top size. See also: oil agglomeration.

selective crushing
 * Crushing in such a manner as to cause one ingredient of the feed to be crushed preferentially to others.

selective digging
 * Separating two or more types of soil while digging them.

selective filling
 * Hand filling, during which the miner rejects stone or dirt and loads only clean coal. Similar methods are adopted in metal mining.

selective flotation
 * a. A process for the preferential recovery of a particular ingredient of the coal, e.g., a petrological constituent, by froth flotation.

b. Generally refers to the surface or froth selecting of the valuable minerals rather than the gangue. Sometimes used to mean differential flotation. See also: flotation; preferential flotation.

selective grinding
 * Grinding in such a manner as to cause one ingredient of the feed to be ground preferentially to others.

selective mining
 * a. A method of mining whereby ore of high value is mined in such a manner as to make the low-grade ore left in the mine incapable of future profitable extraction. In other words, the best ore is selected in order to make good mill returns, leaving the low-grade ore in the mine. Frequently called robbing a mine. CF: bulk mining.

b. The object of selective mining is to obtain a relatively high-grade mine product; this usually entails the use of a much more expensive stoping system and high exploration and development costs in searching for and developing the separate bunches, stringers, lenses, and bands of ore. In general, selective methods are applicable where the valuable sections of the deposit are rather large, comparatively few in number, and separated by relatively large volumes of waste. Selective methods of stoping are square-set stoping, open stoping in low-dipping beds, and cut-and-fill stoping. c. In coal mining, selective methods may be dictated by market demands and prices. It may be desirable to work the different quality coal seams in such proportions as to obtain a uniform and salable blend over a period of years. In metal mining, the stopes may be restricted in both length and width and thus produce a much higher grade of ore. It is not always practicable to resort to selective mining because the mineralization may be so distributed as to necessitate taking the whole orebody in mining operations.

selective reflection
 * The reflection by a substance, such as an opaque gem, of light rays of only certain wavelengths, the others being absorbed. This cause of color in gems is a sort of selective absorption.

selective weathering
 * See: differential weathering.

selective wetting
 * In mineral processing, development of selective attraction to the water phase of a pulp, as a prelude to flotation of an air-attracted fraction of the contained minerals.

selectivity index
 * Criterion of trend in a continuous operation such as mineral processing. Abbrev., S.I.

selector
 * In copper smelting, a kind of converter with horizontal tuyeres, to produce bottoms and a purified copper in one operation.

select round
 * Sometimes used to designate the best quality of industrials normally used as drill diamonds.

selenite
 * a. Finely crystallized gypsum.

b. A clear, colorless variety of gypsum, occurring (esp. in clays) in distinct, transparent monoclinic crystals or in large crystalline masses that cleave easily into broad folia. Syn: spectacle stone.

selenite plate
 * In mineralogy, a plate of selenite that gives a purplish-red interference color of the first order with crossed polars. Syn: gypsum plate; unit retardation plate; sensitive-tint plate; first-order red plate; Red I plate; Rot I plate.

selenium
 * A nonmetallic element and member of the sulfur family. Symbol, Se. It is widely distributed in small quantities, usually as selenides of heavy metals. Obtained from electrolytic copper refining. Used in photocells, exposure meters, and solar cells, and extensively in rectifiers.

selenjoseite
 * See: laitakarite.

selenolite
 * a. Wadsworth's name for rocks composed of gypsum or anhydrite.

b. A mineral, Pb (sub 2) (SeO (sub 4) )(SO (sub 4) ), reported as white needles with cerussite and molybdomenite at Cacheuta, Argentina. c. Former name for olsacherite. d. Discredited name for downeyite, SeO (sub 2).

self-act
 * See: gravity haulage.

self-acting door
 * A ventilation door consisting of two halves, so constructed that they are forced apart centrally by the trams as they come in contact with the converging beams that operate them. The door halves move on small pulleys that run on inclined rails so that after the passage of the trams the door closes by gravity.

self-acting incline
 * a. In transport by mine car, a brake incline. See also: brake incline.

b. See: gravity haulage.

self-acting plane
 * An inclined plane upon which the weight or force of gravity acting on the full cars is sufficient to overcome the resistance of the empties; in other words, the full car, running down, pulls the other car (empty) up.

self-acting rope haulage
 * A system of rope haulage used for transporting material on the surface and to transfer loaded cars from one elevation to a lower one in mines. Slope must be sufficiently steep so the loaded cars will pull the empty cars up the grade. Syn: gravity plane rope haulage.

self-advancing supports
 * An assembly of hydraulically operated steel hydraulic supports, on a longwall face, that are moved forward as an integral unit by means of a hydraulic ram coupled to the heavy steel face conveyor. Syn: power-operated supports; walking props. See also: hydraulic chock; steel prop.

self-aligning carrying idler
 * A belt idler that controls and limits the side runout of the carrying belt within practical limits by means of a swivel mechanism.

self-aligning return idler
 * A belt idler that controls and limits the side runout of the return belt within practical limits by means of a swivel mechanism.

self-annealing
 * A term applied to metals, such as lead, tin, and zinc, that recrystallize at air temperature and in which little strain hardening is produced by cold working.

self-centering chuck
 * A drill chuck that, when closed, automatically positions the drill rod in the center of the drive rod of a diamond-drill swivel head.

self-cleaning tail pulley
 * A conveyor belt structure tail pulley which is designed with vanes along the length of the tail pulley and often is hollow in the center to allow any spillage along the return belt to end up at the tail pulley, which allows it to fall to the sides to eliminate the debris.

self-cleansing gradient
 * The gradient at which flow in a pipe of a particular diameter will carry away any solids in it. This gradient must not be too steep nor too gradual, and is usually established under local laws affecting drains and sewers.

self-contained breathing apparatus
 * A self-sufficient breathing unit that permits freedom of movement, unencumbered by air hoses. It offers the wearer respiratory protection in atmospheres that are either oxygen-deficient or too highly toxic to permit the use of gask masks or respirators. The oxygen or air is supplied in compressed form or by chemical generation, and the wearer's exhalations are either purified for re-use or released to the surrounding atmosphere. The equipment is devised to afford protection for special lengths of time, in accordance with the standards set by the Mine Safety and Health Administration. The 2-h apparatus is used for mine rescue and recovery operations; shorter period apparatus is available for industrial uses and auxiliary equipment.

self-contained portable electric lamps
 * Electric lamps that are operated by an electric battery; designed to be carried about by the user of the lamp.

self-contained self-rescuer
 * A respiratory device used by miners for the purpose of escape during mine fires and explosions; it provides the wearer a closed-circuit supply of oxygen for a minimum of 10 min and up to 1 h. Syn: SCSR.

self-diffusion
 * The spontaneous movement of an atom to a new site in a crystal of its own species, such as a copper atom within a crystal of copper.

self-dumping cages
 * Cages in which the cars are generally fitted with end doors; the cage deck is pivoted, and a roller engages with a tipping guide at the surface. As the cage is lifted, toward the end of the wind the deck tilts, the end door is lifted, and the coal is discharged.

self-dumping car
 * A mine car that can be side-tipped while in motion on a rail track. A ramp structure is fitted alongside the track opposite the spot where tipping is required. The car is fitted with a spherically contoured wheel that engages the ramp and gradually tilts the car while in motion. A chain attachment to the underframe opens the side of the car when tilted for tipping. The ramp can be retracted when not required.

self-energizing brake
 * A brake that is applied partly by friction between its lining and the drum.

self-feeder
 * An automatic appliance for feeding ore to stamps or crushers without the employment of hand labor.

self-feeding portable conveyor
 * Any type of power-propelled conveyor designed to advance into a pile of bulk material, thereby automatically feeding itself.

self-fluxing ores
 * Ores that contain both acid and basic gangue minerals in the proper ratio to form a suitable slag.

self-inductance
 * The property of a circuit whereby self-induction occurs. It is measured by the rate of change of linkages in a circuit that accompanies a rate of change of current in that circuit of one unit per second.

self-issue system
 * A system of storage in lamp-room-operation charging and issue for alkaline-type car lamps, that allows a user access only to the storage racks for the purpose of lamp collection or return. Charging is controlled by a lamp-room attendant.

self-loading dumper
 * A dumper provided with a bucket, hinged by arms to the chassis, that scoops up the material and discharges it backwards into the hopper. Hydraulic rams control the lift arms, bucket movement, and dumping operation.

self-opening reamer
 * An underreamer having cutters that expand when they come in contact with, and are pressed against, surface. CF: expansion bit; underreamer.

self-potential
 * See: spontaneous.

self-potential curve
 * See: spontaneous potential curve.

self-potential log
 * Strip recording of natural potentials of complex origin, arising in the immediate neighborhood of liquid-filled boreholes. See also: electric logging.

self-potential method
 * An electrical exploration method in which one determines the spontaneous electrical potentials (spontaneous polarization) that are caused by electrochemical reactions associated with clay or metallic mineral deposits. Syn: spontaneous-potential method.

self-potential prospecting
 * A method of electrical prospecting based on the measurement of natural earth potentials caused by the self-potential effects from orebodies, commonly metallic sulfides.

self-powered scraper
 * A scraper built into a single unit with a tractor.

self-priming centrifugal pump
 * A pump of the centrifugal type that combines in a single hydraulic stage and with a single hydraulic impeller and casing the dual ability to pump, under vacuum, either liquids or gases. These pumps are advantageously used for sump, bilge, mine water gathering, tankcar unloading, vacuum evaporator applications, chemical processing, and other uses where the liquid is below the pump centerline, or under high vacuum. The suction lift is usually guaranteed at 20 ft (6.1 m) for cold water at sea level.

self-reading staff
 * A leveling staff, marked with graduations so that an observer looking through the telescope of a level can read the elevation at which his or her line of sight intersects the staff.

self-rescuer
 * A small filtering device carried by a miner underground, either on a belt or in a pocket, to provide the miner with immediate protection against carbon monoxide and smoke in case of a mine fire or explosion. The device is used for escape purposes only because it does not sustain life in atmospheres containing deficient oxygen. The length of time a self-rescuer can be used is governed mainly by the humidity in the mine air; e.g., in moist air it will last for a minimum period of 30 min, and in moderately dry atmospheres, for a period of 1 h or more. See also: Siebe-Gorman self-rescuer.

self-service system
 * A system of storage and issue for lead-acid-battery-operated lamps, whereby the user has direct access to the charging racks for the purpose of connecting or disconnecting a lamp from the charging circuit. See also: attendance signaling system; lamp room.

self-shooter
 * See: booming; flop gate.

self stones
 * Fragments of rocks still possessing the original shape and angles, Derbyshire, U.K.

self-stowing gate
 * Applied to an advance gate that carries forward a waste or skip, from 6 to 10 yd (5.5 to 9.1 m) wide, to take all the broken rock produced by the gate rippings. A short face conveyor is usually used to move the coal and dirt as required. The width of the waste is just sufficient for stowing the dirt produced. See also: deepside.

self-timing anemometer
 * An anemometer that has a timing device incorporated in it. Twenty seconds after being started, the device automatically engages the pointer with the rotating vanes and after an interval of 1 min disengages it. See also: anemometer.

seligmannite
 * An orthorhombic mineral, CuPbAsS (sub 3), with As replaced by Sb toward bournonite; forms small, lead-gray, complex crystals.

sellaite
 * A tetragonal mineral, MgF (sub 2) ; colorless; structurally related to rutile.

selvage
 * a. The altered, clayey material found along a fault zone; fault gouge. Syn: selvedge. See also: gouge; flucan.

b. A marginal zone of a rock mass, having some distinctive feature of fabric or composition; specif. the chilled border of an igneous mass (as of a dike or lava flow), usually characterized by a finer grain or sometimes a glassy texture, such as the glassy inner margins on the pillows in pillow lava. Syn: selvedge; salband.

selvedge
 * See: selvage.

Selvulize system
 * A cold vulcanizing method for use underground. It is simpler and quicker than hot vulcanizing and there is no fire or explosion risk involved.

semianthracite
 * The rank of coal, within the anthracitic class of Classification D 388, such that, on the dry and mineral-matter-free basis, the volatile matter content of the coal is greater than 8% but equal to or less than 14% (or the fixed carbon content is equal to or greater than 86% but less than 92%), and the coal is nonagglomerating.

semiarid
 * Said of a type of climate in which there is slightly more precipitation (25 to 50 cm) than in an arid climate, and in which sparse grasses are the characteristic vegetation. Syn: subarid.

semiautomatic control
 * A system to control the speed of a winder consisting of a cam-operated rheostat in parallel with a manually operated winder controller, the instantaneous cam position being directly related to the position of a cage in the shaft. If the driver left the manual control in the full-speed position, the cam control and associated closed-loop control would take charge and automatically decelerate the winder to creep speed as the cage approaches the surface. Should the driver still defer the operation of the lever, the winder would stop on the operation of an overwind limit switch. By the introduction of a small switch to initiate the wind and another to terminate the wind, fully automatic operation is possible. See also: automatic cyclic winding.

semicircumferentor
 * A surveyor's instrument used for setting out land or buildings to any angle and in preliminary survey work generally and made up of a horizontal graduated semicircle that surrounds a compass and is attached to a base with fixed vertical sights at each end and of a movable arm with vertical sights at each end that pivots on the center of the base. See also: surveyor's compass.

semicontinuous mill
 * One that incorporates some stands in tandem, either for roughing or finishing, an example being a semicontinuous wire rod mill with a continuous roughing train and a looping finishing train.

semicoring bit
 * A noncoring bit that produces a small-diameter core.

semicrystalline
 * See: hyalocrystalline.

semidry mining
 * a. Underground work in which humidity of ventilating air is kept low, though moisture is used in drilling to allay dust.

b. In semidry mining, every effort is made to prevent the ventilating air from picking up moisture in the downcast shafts and in the main ways leading to the workings. In the workings themselves, moisture is added freely in order to reduce dust, and the air rapidly becomes saturated.

semiduplex process
 * The process consists essentially of pouring molten metal from a primary open-hearth furnace on a heated solid charge of heavy and light alloy scrap (20% to 40% of total). The charge is melted and finished under reducing conditions. There is no boil.

semifusain
 * A coal constituent transitional between vitrain and fusain. It displays gradual disappearance of cell structure, hardness, and yellowish color when observed in thin sections. Same as vitrifusain.

semifusinite
 * A constituent intermediate between vitrinite and fusinite showing a well-defined structure of wood and sclerenchyma. The cell cavities, either round, oval, or elongated in cross section, vary in size but are generally smaller and sometimes less well defined than those of fusinite. Occurs as lenses and bands of variable thickness, and as small fragments; associated with fusinite, or included in vitrite, clarite, duroclarite, clarodurite, and durite. It often lies as a transition material between vitrinite and fusinite, and the properties lie between those of fusinite and vitrinite; behaves as a semi-inert diluent in carbonization.

semigelatin
 * Dynamite containing both ammonium nitrate as the chief explosive ingredient and a certain percent of blasting gelatin to make it plastic enough to remain in holes directed upward. It is more resistant to water than ammonia dynamite, but less resistant than gelatin dynamite.

semihorizon mining
 * Coal mining that consists of driving cross-measure drifts and developing of the seams. The roads in the seam are equipped with conveyors for transporting coal, and locomotives may be used in the cross-measure drifts when these are horizontal or nearly so. Semihorizon mining may include the longwall-retreating method.

semikilled steel
 * Steel that is incompletely deoxidized and contains sufficient dissolved oxygen to react with the carbon to form carbon monoxide to offset solidification shrinkage.

semiloose
 * In an excavation, both rock that is only partially detached from the solid and that rings as solid when struck, and rock being still attached to the solid, but parting from it by incipient shear cracks.

semimetallic pellets
 * See: prereduced iron-ore pellet.

semimuffle furnace
 * A furnace with a partial muffle, in which the products of combustion come in contact with the ware.

semiopal
 * A loosely used term for common opal, hydrophane, and any partly dehydrated or impure opal, as distinguished from precious opal or fire opal. Syn: hemiopal.

semiplastic explosives
 * In these types, the quantities of liquid products are insufficient to render the mixture compressible. When packing cartridges, however, the same high density is obtained as with plastic explosives. The proportions of the various constituents are actually so arranged that the spaces between the grains are filled out. The proportions in question are determined entirely according to the constituents selected.

semiportable electric equipment
 * Electric equipment that is moved infrequently; e.g., room hoists, room conveyors, and gathering pumps.

semiportable electric lamps
 * Electric lamps that are connected to a fixed source of power by a flexible cord whose length limits the movable range of the lamp.

semiprecious
 * Of less commercial value than those called precious; applied esp. to such stones as amethyst, garnet, jade, and tourmaline.

semiround nose
 * A bit-crown design, in which the radius of the arc forming the rounded portion of the bit face is equal to or greater than the thickness of the bit wall.

semisolid bituminous material
 * Material having a penetration at 77 degrees F (25 degrees C), under a load of 100 g applied for 5 s, of more than 10; and a penetration at 77 degrees F, under a load of 50 g applied for 1 s, of not more than 350.

semisplint coal
 * a. Coal intermediate between durain coal and clarain coal (duroclarain).

b. A coal in which the proportions of anthraxylon and attritus are more or less equal, but the attritus of which is essentially composed of brown and granular opaque matter in varying proportions. Translucent humic matter, spores, pollens, and finely divided fusain are always present in small proportions. Also known as block coal. CF: bright coal; splint coal. c. A banded coal containing 20% to 30% of opaque attritus and more than 5% anthraxylon.

semitrailer
 * A towed vehicle whose front rests on the towing unit.

semitranslucent
 * A degree of diaphaneity between translucent and opaque. Passes light through edges of cabochons but very little through thicker parts.

semitransparent
 * Used to describe mineral when objects may be seen through it but without distinct outlines.

semivitreous
 * That degree of vitrification evidenced by a moderate or intermediate water absorption. Also called semivitrified. See also: impervious; nonvitreous; vitreous.

semiwater gas
 * A mixture of carbon monoxide, carbon dioxide, hydrogen, and nitrogen obtained by passing a mixture of air and steam continuously through incandescent coke. Its calorific value is low, about 125 Btu/ft (super 3) (4.66 MJ/m (super 3) ).

semseyite
 * A monoclinic mineral, Pb (sub 9) Sb (sub 8) S (sub 21) ; metallic; soft; sp gr, 5.8. (super )

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