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

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A solution obtained by leaching; e.g., water that has percolated through soil containing soluble substances and that contains certain amounts of these substances in solution. Syn: lixivium.

leach dump

Low-grade ores that are dumped loosely in piles on soil surfaces so that fluids may be sprinkled on the piles to leach recoverable metals.

leached zone

The part of a lode above the water table, from which some ore has been dissolved by down-filtering meteoric or spring water.


In ore dressing, smelting, and refining, one who dissolves valuable metal out of ore or slime, using chemical solution.

leach hole

See: sinkhole.


a. The separation, selective removal, or dissolving-out of soluble constituents from a rock or orebody by the natural action of percolating water.

b. Dissolution from ore or concentrates after suitable comminution to expose the valuable minerals, by aqueous and chemical attack. If heat and pressure are used to intensify or speed this, the work is called pressure leaching. See also: chemical extraction; hydrometallurgy. c. The removal in solution of nutritive or harmful constituents (such as mineral salts and organic matter) from an upper to a lower soil horizon by the action of percolating water, either naturally (by rainwater) or artificially (by irrigation). d. The extraction of soluble metals or salts from an ore by means of slowly percolating solutions; e.g., the separation of gold by treatment with a cyanide solution. Syn: lixiviation.

leaching rate test

A test designed to assess the value of antifouling compositions by measuring the rate of loss of toxic ingredients from a painted surface during immersion in seawater.

leach material

Material sufficiently mineralized to be economically recoverable by selectively dissolving the wanted mineral in a suitable solvent. See also: leaching.

leach pile

Mineralized materials stacked so as to permit wanted minerals to be effectively and selectively dissolved by application of a suitable solute.

leach precipitation float

A mixed method of chemical reaction plus flotation developed for such copper ores as chrysocolla and the oxidized minerals. The value is dissolved by leaching with acid, and the copper is reprecipitated on finely divided particles of iron, which are then recovered by flotation, yielding an impure concentrate in which metallic copper predominates. Abbrev., L.P.F.


a. A bluish-white metal of bright luster, very soft, highly malleable, ductile, and a poor conductor of electricity; very resistant to corrosion; a cumulative poison. Symbol, Pb. Rarely occurs in native form; chiefly obtained from galena (PbS). Lead is used in storage batteries, cable covering, plumbing, ammunition, antiknock gasoline, radiation shielding, and to absorb vibration. Other lead compounds are used in paints, fine glass, and lenses. Environmental concern with lead poisoning has resulted in a U.S. national program to reduce the concentration of lead in gasoline.

b. An open watercourse, usually artificial, leading to or from a mill, mine, or reservoir. Syn: leat. c. See: ledge; lode. CF: blind lead. Pron. leed. d. A placer deposit. CF: blue lead; deep lead. Pron. leed. e. A defined gutter of auriferous wash. Pron. leed. f. A track haulage term for the distance from the point of a frog to the point of the switch. Pron. leed. g. A term sometimes used for the distance between the sheave and the winding drum centers. The greater the lead, other things being equal, the smaller the fleeting angle. Too great a lead results in vibration and whipping of the rope between sheave and drum. Idler or sag rollers are frequently installed where long leads are necessary. Pron. leed. h. The distance a bit is held suspended off bottom in a borehole before rotation and downward movement of the drill string is started. Pron. leed. i. Commonly used synonym for ledge or lode. Many mining location notices describe the locator's claim as extending a certain number of feet along and so many feet on each side of the lode, lead, vein, or ledge. Thus Lead, S. Dak., was so named because of the Homestake lead. Blind lead: A lead or vein that does not outcrop or show at the surface. Used esp. at Virginia City, NV. CF: lode. Pron. leed. j. Properly, placer gravels. Blue lead: A Tertiary river channel at Placerville, CA. So called because of the bluish-gray color of the gravels. Deep lead: Goldbearing gravels deeply covered with debris or lava applied particularly to those of Victoria, Australia. Pron. leed. k. The longitudinal distance traveled in one revolution by a spiral thread or screw. Pron. leed.

lead-acid accumulator

A secondary cell battery with an electromotive force of about 2 V. It is suitable for work where a steady voltage is required, and extensively used for motor car lighting, miners' safety lamps, shuttle cars, and battery locomotives.


The distance coal has to be hauled from the mine to its place of shipment.

lead azide

A nitrite of lead, Pb(N (sub 3) ) (sub 2) , used as an initiating explosive in blasting caps.

lead bath

A furnace in which gold or silver ores are smelted with lead.

lead button

In the separation of the noble metals from their impurities, lead is fused with the ore. The bullion so formed drops to the bottom of the crucible in the lead button from which the precious metal is extracted by cupellation. Syn: crucible assay.

lead carbonate

See: cerussite; white lead ore.

lead edge

The surfaces or inset cutting points on a bit that face in the same direction as the rotation of the bit.


a. A narrow vein branching upwards at an angle from a much larger vein. See also: dropper.

b. A thin layer of coal, coaly shale, or ironstone that serves as a guide or datum toward workable beds in a mine.


Guides in a pile frame to take the drop hammer of a pile driver.

lead feldspar

Synthetic PbAl (sub 2) Si (sub 2) O (sub 8) .

lead fume

The fume escaping from lead furnaces and containing both volatilized and mechanically suspended metalliferous compounds.

lead glance

See: galena.


A monoclinic mineral, 8[Pb (sub 4) (SO (sub 4) )(CO (sub 3) ) (sub 2) (OH) (sub 2) ] ; trimorphous with macphersonite and susannite; soft; may fluoresce yellow; in oxidized zones of lead-ore deposits.

leading heading

The one of a pair of parallel headings that is kept a short distance in advance of the other. This may be adopted to drain the water and thus secure one dry heading. The term is also applied to a heading that is driven in the solid coal in advance of the general line of face.

leading place

Scot. A working place in advance of the others, such as a heading or a level.


Derb. Small sparry veins in the rock. Syn: leader.

leading stone

See: lodestone.

leading winning

Aust. A heading in advance of the ordinary bords. A leading bank.

leading wire

An insulated wire strung separately or as a twisted pair, used for connecting the two free ends of the circuit of the blasting caps to the blasting unit. See also: leads.

lead lap

a. A gem cutter's lap, of lead, copper, or iron; also, the entire machine.

b. In mechanics, a lap of lead charged with emery and oil.

lead metacolumbate

Pb(CbO (sub 3) ) (sub 2) ; a ferroelectric material with a Curie temperature of 570 degrees C. The material can be polarized to obtain piezoelectric properties. Uses include high-temperature transducer applications, sensing devices, and accelerometers. Syn: lead metaniobate.

lead metaniobate

See: lead metacolumbate.

lead metasilicate

See: alamosite.

lead motorman

In ore dressing, smelting, and refining, a person who operates a small electric locomotive (motor) to haul pots of molten lead bullion from a blast furnace to refining kettles for the separation of copper, antimony, silver, and other metals contained in the lead bullion.

lead niobate

Pb(NbO (sub 3) ) (sub 2) ; a ferroelectric compound having properties that make it useful in high-temperature transducers and in sensing devices. The Curie temperature is 570 degrees C.

lead ocher

See: massicot; litharge.

lead of a switch

The distance measured on the main line from the point of switch to the point of frog. Also called frog distance.

lead rail

The lead rail of an ordinary mine switch is the turnout rail lying between the rails of the main track.


The wires, forming part of an electric detonator, to which the shot-firing cable is attached.

lead selenide

See: clausthalite.

lead silicate

See: alamosite.

lead spar

See: cerussite; anglesite.

lead sulfide

See: galena; glance.

lead tantalate

PbTa (sub 2) O (sub 6) ; a compound believed to have ferroelectric properties and of possible interest as a special electroceramic. The Curie temperature is 260 degrees C.

lead tree

A crystalline deposit of metallic lead on zinc that has been placed in a solution of acetate of lead.

lead-uranium ratio

The ratio of lead-206 to uranium-238 and/or lead-207 to uranium-235, formed by the radioactive decay of uranium within a mineral. The ratios are frequently used as part of the uranium-thorium-lead age method.

lead vitriol

See: anglesite.

lead-well man

In ore dressing, smelting, and refining, a person who maintains flow of molten lead from the blast furnace to the lead pot for removal to refinery.

lead wires

a. In blasting, the heavy wires that connect the firing current source or switch with the connecting or cap wires.

b. Two insulated copper wires leading from the battery or igniting apparatus to the primer cartridge in an explosive charge. Also called connecting wires.

lead works

A place where lead is extracted from the ore.

lead zirconate

PbZrO (sub 3) ; a ferroelectric material. It is also used in lead titanate-zirconate (P.Z.T) piezoelectric ceramics.


A very thin sheet or plate of metal, as gold.

leaf clay

See: book clay.


a. Any of various linear units of distance, ranging from about 2.42 to 4.6 statute miles (3.89 to 7.4 km); esp. land league (an English land unit equal to 3 statute miles or 4.83 km) and marine league (a marine unit equal to 3 nmi or 5.56 km).

b. Any of various units of land area equal to a square league; esp. an old Spanish unit for the area of a tract 5,000 varas square, equal to 4,428.4 acres (1,792.1 ha) in early Texas land descriptions or equal to 4,439 acres (1,796 ha) in old California surveys.


Low-grade mineralized rock into which an orebody degenerates.


An unintentional diversion of ventilation air from its designed path.

leakage coefficient

A numerical expression of a duct's liability to leak. The National Coal Board of Great Britain defines this as the volume of air in cubic feet per minute that would leak from 100 ft (30 m) of a ventilation duct under a uniform pressure of 1 in (2.54 cm) of water gage.

leakage halo

A dispersion pattern formed by the movement of ore-forming fluids in the rock overlying a mineral deposit.

leakage intake

An additional intake that is a component part of a system of controlled leakage.

leakage intake system

A ventilation circuit with two adjacent intake roadways leading to the coalface. The method has been criticized because the air flow may become so sluggish as to cause combustible gases layers. See also: two intakes.

leakage resistance

The resistance between the blasting circuit, including lead wires, and the ground.

leak vibroscope

An instrument that detects leaks in water, oil, gas, steam, and air lines by amplifying the sound produced by the escaping fluid.


a. Of ore, low-grade; submarginal; unpay; of doubtful exploitable value.

b. A rock in which the minerals sought occur in much less than exploitable amounts. c. See: hang. d. See: low-grade.

lean clay

A clay of low to medium plasticity owing to a relatively high content of silt or sand. CF: fat clay.

lean ore

A low-grade ore. See also: lean; natural ore.


Eng. A dislocation of strata by faulting.

leapfrog system

A system employed with self-advancing supports on a longwall face in which alternate supports are advanced on each web of coal removed. To do this, alternate units have to be moved a distance equal to twice the web thickness--half before snaking and half after snaking.


See: lehr.


Eng. Empty places; old workings.

leasable minerals

A legal term that for Federally owned lands, or Federally retained mineral interest in lands in the United States, defines a mineral or mineral commodity that is acquired through the Mineral Lands Leasing Act of 1920, as amended; the Geothermal Steam Act of 1970, as amended; or the Acquired Lands Act of 1947, as amended. These Acts are found in Title 30 of the United States Code - Mineral Lands and Mining. The leasable minerals include oil, gas, sodium, potash, phosphate, coal, and all minerals within Acquired Lands. Acquisition is by application for a Government lease and permits to mine or explore after lease issuance.


a. A contract between a landowner and another, granting the latter the right to search for and produce oil or mineral substances upon payment of an agreed rental, bonus, and/or royalty.

b. The instrument by which such grant is made. c. A piece of land leased for mining purposes. See also: claim; concession system; royalty.


A Western colloquiallism meaning lessee.

Leasing Act Minerals

Deposits of coal, phosphate, oil, oil shale, gas, sodium, potassium and sulfur that can be leased from the U.S. Government under the Mineral Leasing Act for acquired lands.


a. A mill stream used by small mines for power generation.

b. A ditch that leads water to mineral workings.


See: mountain leather.


Corn. The mineral left after the good ore has been removed; tailings.


Naturally fused gray siliceous glass; actually a minor rock type varying in composition according to the original sand type, typically 90% to 99.5% silica. CF: fulgurite; impactite. Also spelled lechatelierite.

lechosos opal

A variety of precious opal exhibiting a deep green play of color; esp. a Mexican opal exhibiting emerald-green play of color and flashes of carmine, dark violet, dark blue, and purple.


An orthorhombic mineral, (NH (sub 4) ,K)Na(SO (sub 4) ).2H (sub 2) O ; occurs in bat guano.


N. of Eng. A spare tub, or one that is being loaded while another is being emptied.


a. A narrow shelf or projection of rock, much longer than wide, formed on a rock wall or cliff face.

b. A rocky outcrop; solid rock. c. An underwater ridge of rocks, esp. near the shore; also, a nearshore reef. d. A quarry exposure or natural outcrop of a mineral deposit. e. A bed or several beds in a quarry or natural outcrop, particularly those projecting in a steplike manner. f. The surface of such a projecting bed. g. In mining, a projecting outcrop or vein, commonly of quartz, that is supposed to be mineralized; also, any narrow zone of mineralized rock. h. A mass of rock that constitutes a valuable mineral deposit. i. A colloquial syn. of bedrock, used in northern Michigan. j. The only true ledges are deposits of oil-shale, slate, or the like. A ledge is a horizontal layer, therefore a vein or lode is not a ledge. k. A rocky formation continuous with and fringing the shore. Syn: lead.

ledge rock

True bedrock. CF: false bottom.

Leebar separator

A dense medium washer consisting of a static bath. The floats, or clean coal, are removed by means of paddles or chains suspended from bars connected to rotating spokes. The sinks, or shale, are extracted by a scraper device. The bath can be fed directly from the raw coal screens. The separator has been developed for the treatment of large coal. See also: Nelson Davis separator.

Lee configuration

a. An electrical resistivity measuring method using two current electrodes and three equispaced potential electrodes.

b. A configuration employing electrodes, the outer two of which are the current and the inner three of which are the potential electrodes. Syn: partitioning method.


A reddish variety of potassium feldspar.

Lee-Norse miner

A continuous miner, developed in the United States, for driving headings in medium or thick coal seams. It weighs about 26 st (23.6 t), and makes a cut 8-1/2 ft (2.6 m) wide, gathers the cut coal and loads it into cars or conveyor at a rate up to about 4 st/min (3.6 t/min). It can work in seam heights from 3 ft 8 in (1.1 m) up to about 10 ft (3 m). It consists, mainly, of a boom carrying the cutting head; the gathering head, and at the rear the jib support frame on which the jib can be slewed. The machine is operated by hydraulic motors.


See: lehr.


In glassmaking, the process of treating in the annealing oven or leer.

Leet seismograph

A portable three-component seismograph designed primarily for registration of vibrations from blasts, traffic, machinery, and general industrial sources.


A bleached-white variety of asbestiform chrysotile from Mt. Troodos, Cyprus.

left bank

The bank of a stream that is to the left of an observer facing downstream.

left lang lay

Wire or fiber rope or cable in which the wires or fibers in a strand and the strands themselves are twisted to the left.

left-lateral fault

A fault on which the displacement is such that the side opposite the observer appears displaced to the left. CF: right-lateral fault. Syn: sinistral fault.

left long lay

See: left lang lay.

left regular lay

Wire or fiber rope or cable in which the individual wires or fibers in the strands are twisted to the right and the strands to the left. Syn: regular-lay left lay.

left twist

See: right lay. Corresponds to a right-hand screw thread.


a. In mine timbering, a prop or upright member of a set or frame. Also called upright; post; arm.

b. One of the main upright members of a drill derrick or tripod. c. A term sometimes applied to a centrifugal discharge bucket elevator. Usually a double leg bucket elevator. d. See: draft. e. A side post in tunnel timbering.


A brief explanatory list of the symbols, cartographic units, patterns (shading and color hues), and other cartographic conventions appearing on a map, chart, or diagram. On a geologic map, it shows the sequence of rock units, the oldest at the bottom and the youngest at the top. The legend formerly included a textual inscription of, and the title on, the map or chart. Syn: key.

leg piece

The upright timber that supports the cap piece in a mine. CF: legs.


A monoclinic mineral, 8[Zn (sub 2) (AsO (sub 4) )(OH).H (sub 2) O] .


a. The wires attached to and forming a part of an electrical blasting cap.

b. The uprights of a set of mine timbers. See also: dap; leg piece.


Sp. Land league used in the original surveys of the Philippines, California, and Texas. It is equal to 2.63 miles or 4.24 km. See also: league.

leg wire

One of the two wires attached to and forming a part of an electric blasting cap or squib.

Lehigh jig

A plunger-type jig with the following distinguishing characteristics: (1) the plunger contains check valves that open on the upstroke to reduce suction; (2) the makeup water is introduced with the feed; (3) the screen plate is at two levels, which have different perforations, to keep the water distribution uniform; (4) the bottom of the discharge end of the jig is hinged. This jig has been used extensively in washing anthracite.


A mixture of crandallite with other minerals.

Lehmann process

A process for treating coal by disintegration and separation of the petrographic constituents (fusain, durain, and vitrain). It consists of subjecting the coal to resilient disintegrating or shattering action for a sufficient length of time to break the constituents into granules of various sizes by reason of their respective resistances to shattering impacts and separating the granules into different sizes by screening or equivalent means.


An enclosed oven or furnace used for annealing, or other form of heat treatment; particularly used in glass manufacture. It is a kind of tunnel down which glass, hot from the forming process, is sent to cool slowly, so that strain is removed, and cooling takes place without additional strain being introduced. Lehrs may be of the open type (in which the flame comes in contact with ware), or of the muffle type. Syn: leer; lear.

lehr man

Person who regulates temperature of a reheating oven (lehr) used to fire-glaze glass articles. Arranges glass articles according to size and shape on lehr conveyor so that maximum quantity will be carried in oven on a long paddle. Also called leer man; lehr operator, glass; lehr tender.


See: ludlamite.


A triclinic mineral, K (sub 2) Ca (sub 2) Cu(SO (sub 4) ) (sub 4) .2H (sub 2) O ; pseudo-orthorhombic; blue; at Chuquicamata, Chile.

Leitz tyndallometer

Measures the intensity of the light scattered at an angle from the incident beam by a dust cloud, and correlates well with the concentration determined by the thermal precipitator or the surface area calculated from such a count. However, it needs to be calibrated for each type of dust cloud, owing to difference in mineralogical content, against the thermal precipitator.

Lemberg's solution

Logwood digested in an aqueous solution of aluminum chloride; used to distinguish calcite and dolomite. Calcite and aragonite are stained violet after treatment for about 10 min, but dolomite remains unchanged.


A contracted form of the names leucite and nephelite; suggested as an alternative group name for the feldspathoid minerals. CF: feldspathoid.


A triclinic mineral, Pb (sub 6) (Ag,Cu) (sub 2) As (sub 4) S (sub 13) .

lengthening rod

A screwed extension rod for prolonging a well-boring auger or bit.

length fast

See: negative elongation.

length of lay

The distance measured along a straight line parallel to the rope in which the strand forms one complete spiral around the rope or the wires around the strand. See also: lay.

length of shot

a. The depth of the hole in which the powder is placed, or the size of the block of coal to be loosened by a single blast measured parallel with the hole.

b. In open pit mining, the distance from the first drill hole to the last drill hole along the bank.


Eng. In tunnel construction, the successive sections in which a tunnel is executed. Shaft lengths are directly under the working shaft; side lengths are on each side of the shaft length; leading lengths are prolongations of the tunnel from the side lengths; and junction lengths complete the portion of the tunnel extending between two shafts, or between a shaft and an entrance.

length slow

See: positive elongation.


a. A green variety of orthoclase at Lenni Mills, Delaware County, PA. Syn: delawarite.

b. A variety of vermiculite.


a. A geologic deposit bounded by converging surfaces (at least one of which is curved), thick in the middle and thinning out toward the edges, resembling a convex lens. A lens may be double-convex or plano-convex. See also: lentil; lenticular. ---v. To disappear laterally in all directions; e.g., a unit is said to lens out within a mapped area.

b. In optics, a device that modulates the direction taken by a transient beam of light.


Pyrite, round or oval in plan and lenticular in section, ranging up to 2 to 3 ft (0.6 to 0.9 m) in thickness and several hundred feet in the greatest lateral dimension, that is found in coalbeds. Sometimes called kidney sulfur.

lens grinding

The process of grinding pieces of flat sheet glass (or pressed blanks) to the correct form of the lens. Cast-iron tools of the correct curvature, supplied with a slurry of abrasive and water, are used.


The thinning-out of a stratum in one or more directions.


a. A large or small lens-shaped stratum or body of rock; a lentil.

b. A lens-shaped rock fragment of any size.


a. Resembling in shape the cross section of a lens, esp. of a double-convex lens. The term may be applied, e.g., to a body of rock, a sedimentary structure, or a mineral habit.

b. Pertaining to a stratigraphic lens or lentil. Syn: lentiform.

lenticular iron ore

Impure concretionary hematite.


A small lentil.


See: lenticular.


a. A minor rock-stratigraphic unit of limited geographic extent, being a subdivision of a formation and similar in rank to a member, and thinning out in all directions; a geographically restricted member that terminates on all sides within a formation. CF: tongue.

b. A lens-shaped body of rock, enclosed by strata of different material; a geologic lens. See also: lenticule; lenticle.

lentil ore

See: liroconite.


a. A soft, earthy, medium-brown coallike substance associated with lignitic outcrops in North Dakota. It is a naturally oxidized form of lignite with variations in color and properties depending upon the extent of weathering. Usually, the material occurs at shallow depths, overlying or grading into the harder and more compact lignite. Of little value as a fuel, it has been used in oil-drilling muds, in water treatment, and in certain wood stains. It is frequently referred to as "slack" because of its texture; however, the term leonardite is finding common usage.

b. A weathering product of subbituminous coal or lignite, rich in humic and fulvic acids and soluble in alkaline water. It is a byproduct of mining near-surface coal seams, and is used as a soil conditioner, additive to drilling mud, and binder for taconite iron ore (Fowkes & Frost, 1960). Not to be confused with leonhardite or leonhardtite.

Leon combustible gases tester

A combustible gases detector developed in 1902. A form of Wheatstone bridge is used and changes in electrical resistance due to temperature differences are measured. The combustible gases/air sample flows over one set of wires and the gas burns catalytically while the other wires do not come into contact with the sample.


A partially dehydrated variety of laumontite. (Not leonhardtite.)


See: starkeyite. (Not leonhardite.)


A monoclinic mineral, K (sub 2) Mg(SO (sub 4) ) (sub 2) .4H (sub 2) O ; in marine evaporite deposits. Syn: magnesium leonite.


A variety of quartz porphyry containing small phenocrysts of quartz in a microgranitic groundmass of quartz, orthoclase, albite, and mica. The rock has a characteristically spotted or streaked appearance due to staining by hydroxides of iron and manganese.

leopard rock

a. Can. Pegmatitic rocks associated with the apatite veins of Ontario and Quebec.

b. Syenite gneiss consisting of ellipsoidal lumps measuring several inches across and separated by material that is mainly greenish pyroxene. The rock may be slightly schistose.

Leopard stone

Dolomite full of worm castings set in a gray matrix and containing chert nodules, near the base of the Upper Cambrian, Scotland.

Leopoldi furnace

A furnace for roasting mercury ores in a batch process, differing from the Bustamente furnace in having a series of brick condensing chambers.


See: sylvite.


Pertaining to a flaky schistosity caused by an abundance of minerals like micas and chlorites with a general parallel arrangement.


An orthorhombic mineral, 4[gamma-FeO(OH)] ; polymorphous with akaganeite, feroxyhyte, and goethite; yellow to orange-red; the weathering product of iron-bearing minerals; forms the pigment brown ocher; such iron oxyhydroxides constitute the rock limonite.


a. A monoclinic, trigonal, or orthorhombic mineral; 1, 2, or 3[K (sub 2) Li (sub 4) Al (sub 2) (Si (sub 8) O (sub 20) (OH) (sub 4) ] ; mica group; forms a series with muscovite; perfect basal cleavage; pink to purple; in lithium-rich granite pegmatites; a source of lithium. Syn: lithia mica; lithionite.

b. A group name for lithium-rich micas.


A black ferrian variety of biotite.


A variety of phengite, a siliceous variety of muscovite.


See: anorthite.


Said of a hydrothermal mineral deposit formed at temperature and depth conditions intermediate between mesothermal and epithermal; also, said of that environment. CF: hypothermal deposit; xenothermal; telethermal.


A fissile or schistose variety of hornfels containing mica, quartz, and feldspar, with or without accessories, such as andalusite and cordierite. The term was originated by Cordier in 1868. CF: cornubianite.

Lerchs-Grossmann optimization

A mathematical method based on a block model of an orebody used for determining the most profitable optimum shape for an open pit.


See: vermiculite.


a. A mixture of a hydromica and corundum.

b. A potassian variety of margarite.

Lessing process

A heavy-fluid coal-cleaning process in which a calcium chloride solution having a specific gravity of approx. 1.4 is used for the separation, which takes place in a cylindrical tank 6 to 10 ft (1.8 to 3 m) in diameter with a conical bottom, the total height being nearly 30 ft (9.1 m). The cleaned coal rises to the top where it is removed by a chain scraper and delivered to draining towers.

lethal dose

A dose of ionizing radiation sufficient to cause death. Median lethal dose (abbreviated MLD or LD (sub 50) ) is the dose required to kill half of the individuals in a group similarly exposed within a specified period of time. The median lethal dose for humans is about 400 rads.

let into

Eng. The recessing of supports into the floor, side, or roof.


A triclinic mineral, (NH (sub 4) ) (sub 3) H(SO (sub 4) ) (sub 2) ; a decomposition product of pyrite in coal.

letter and tracing cutter

In the stonework industry, a person who cuts incised or raised letters and simple designs on monumental stones with pneumatic and hand tools. Also called letter cutter; letterer.

letter stone

An igneous rock with sheath and core structure giving the appearance of letters on its surface.


See: cyanotrichite; velvet copper ore.


A pale iron-poor variety of clinochlore.


A tetragonal mineral, 16[KAlSi (sub 2) O (sub 6) ] ; a pseudocubic feldspathoid; forms white to gray trapezohedra in potassium-rich, silica-poor lavas. Syn: amphigene; grenatite; white garnet; vesuvian. CF: pseudoleucite.


A fine-grained or porphyritic extrusive or hypabyssal igneous rock chiefly composed of pyroxene (esp. titanaugite) and leucite, with little or no feldspar and without olivine.


See: trapezohedron.


A porphyritic extrusive rock composed chiefly of leucite, nepheline, and clinopyroxene. CF: haueynophyre.


See: olivinite.


Light-colored; applied to igneous rocks that are relatively poor in mafic minerals. The percentage of mafic minerals necessary for a rock to be classified as leucocratic varies among petrologists, but is usually given as less than 30% to 37.5%. CF: melanocratic; mesocratic. Noun, leucocrate. Syn: light-colored.


See: fairfieldite.


A loamlike substance, between a resin and wax in character; C (sub 50) H (sub 84) O (sub 3) ; very impure and sandy as found in a brown coal at Gesterwitz, near Weissenfels, Germany. It crystallizes in white needles from ether and boiling absolute alcohol, and melts above 100 degrees C.


A green to pale-yellow sodium calcium silicate containing beryllium. One of the sources of beryllium. See also: leucophanite.


A triclinic mineral, (Na,Ca) (sub 2) BeSi (sub 2) (O,OH,F) (sub 7) ; pseudo-orthorhombic; a source of beryllium. Syn: leucophane.


A monoclinic mineral, Mn (sub 7) (SiO (sub 4) ) (sub 3) (OH) (sub 2) ; humite group; pseudo-orthorhombic; purple-pink to raspberry-red; in veins associated with manganese ore deposits.


A variety of muscovite.


A term originally applied to altered diabase in which the feldspar has been altered to saussurite, kaolin, and chlorite. This usage is obsolete, but the term is occasionally used for a light-colored hypabyssal rock, being the antithesis of lamprophyre. Not recommended usage.


An oxidized variety of loellingite. See also: loellingite.


A monoclinic mineral, BaNa (sub 4) Ti (sub 2) B (sub 2) Si (sub 10) O (sub 30) ; in alkali pegmatites and the Green River Formation of Utah and Wyoming.


a. Fine-grained, opaque white alteration products of ilmenite, mainly finely crystalline rutile.

b. A variety of sphene.


An embankment beside a river or an arm of the sea, to prevent overflow.


a. A main underground roadway or passage driven along a level course to afford access to stopes or workings and to provide ventilation and a haulageway for the removal of coal or ore. Levels are commonly spaced at regular depth intervals and are either numbered from the surface or designated by their elevation below the top of the shaft. See also: level interval.

b. See: mother gate. c. An instrument for establishing a horizontal line or plane. d. The act or process of adjusting something with reference to a horizontal line. e. In pitch mining, such as anthracite, there may be a number of levels driven from the same shaft, each being known by its depth from the surface or by the name of the bed or seam in which it is driven. f. Applied to seams that run like floors in an office building. Under and above the seam lie the rock strata. g. All openings at each of the different horizons from which the orebody is opened up and mining is started. h. N.S.W. A drive in a mine. i. In speleology, a series of related passageways in a cave, occurring at the same relative, vertical position. j. A gutter for the water to run in.

level course

a. A direction along the strike of an inclined coal seam; a coal seam contour line. The productive faces in a coal mine, such as stalls and conveyor faces are, in general, advanced on level course or slightly to the rise.

b. Scot. In the direction of the strike of the strata, or at right angles to the dip and rise. See also: strike; true dip.

level crosscut

A horizontal crosscut. See also: crosscut.

level drive

A drive that opens up a deposit and makes it accessible along its length and forms the basis for the division of the deposit into levels.


A buck scraper, drag, or any other form of device for smoothing land.


a. War. Old coal or ironstone workings at the outcrop, worked by means of an adit driven into the hillside.

b. A mine that discharges water by gravitation.


The operation of determining the comparative altitude of different points on the Earth's surface, usually by sighting through a leveling instrument at one point to a level rod at another point. Also, the finding of a horizontal line or the establishing of grades (such as for a railway roadbed) by means of a level. Also spelled levelling.

leveling instrument

A surveyor's level bearing a telescope. See also: level.

leveling practice

In leveling, the station is the point at which the staff is held and not the position of the instrument. The operation is one of carrying forward a known level, hence the backsight is a reading taken on the staff at a known elevation and the last sight from each station is called the foresight. All other readings refer to intermediate sights. Leveling sections may be referred to bench marks or to arbitrary levels, but in all cases they must be checked either by closing on the starting point or by starting and finishing on convenient bench marks.

leveling rod

A graduated rod used in measuring the vertical distance between a point on the ground and the line of sight of a surveyor's level.

level interval

a. The vertical distance between the levels turned off the shaft in metal mines for ore intersection and development. The interval varies but may be about 150 ft (46 m).

b. The horizontal distance between levels turned off main development drifts and varies from 200 to 600 yd (180 to 550 m). Levels are usually designated by numbers, names, or depth from the surface.

level-luffing crane

A crane embodying an automatic device that causes the load to move horizontally with any alteration of the operating radius.


Person who operates a surveyor's level.

level of control

A measure of mastery over a process of production; in concrete work, it is measured by cube crushing strength and the standard deviation therefrom. See also: statistical uniformity.

level of saturation

See: water table.


See: level.

level surface

See: equipotential surface.


Person who operates brakes, or levers, at the top of an inclined plane. A brakeman.


a. Separating fine powder from coarser material by forming a suspension of the fine material in a liquid.

b. A means of classifying a material as to particle size by the rate of settling from a suspension. CF: trituration.


In the mineral process of froth flotation, raising of acrophilic particles to the surface of a pulp, by so activating them that they cling to the air-water interface of a rising or coursing air bubble.


A trigonal mineral, (Ca,Na (sub 2) ,K (sub 2) ) (sub 3) Al (sub 6) Si (sub 12) O (sub 36) .18H (sub 2) O ; zeolite group; in cavities in basalts with other zeolites. Also spelled levynite; levyine; levyite.

Leyner-Ingersoll drill

A series of two or more holes drilled as closely together as possible, then connected by knocking out the thin partition between them, forming thus one wide hole, having its greatest diameter in a plane with the desired rift. Blasts from such holes are wedgelike in their action, and by means of them larger and better-shaped blocks can be taken out than would otherwise be possible. �6 �-H +0H Z�;�� � 6 DICTIONARY TERMS:Leyner-Ingersoll drill See: water leyner. See: water leyner.


A peridotite containing both clinopyroxene and orthopyroxene in addition to olivine.


Freeing by comminution, or crushing and grinding, of particles of a specific mineral from their interlock with other constituents of the coal or ore. Also called severance. Syn: unlocking.

liberation of intergrown constituents

Crushing of intergrown material to free the constituent materials.

liberator cells

In electrolytic refining of metals, tanks in which the electrolytic solution is reconstituted.


Gelatinous permissible explosive; used in mining.


An orthorhombic mineral, Cu (sub 2) (PO (sub 4) )(OH) ; olive-green; forms small crystals and druses in copper deposits.

LICADO process

A selective agglomeration process under development, in which the liquid carbon dioxide-water interface is used for the differentiation and separation between coal and mineral matter. The resultant clean coal is a low-sulfur and low-ash content product of relatively low moisture content.

licensed material

Source material, special nuclear material, or byproduct material received, possessed, used, or transferred under a general or special license issued by the Nuclear Regulatory Commission.

licensed store

A place or building licensed by the local authority for the storage of explosives. See also: magazine; registered premises.


a. A short, flattish piece of wood or steel plate wedged over a post, timber set, or steel arch. A lid is used to tighten the support against the ground and also to increase the area supported. See also: clog; wedge.

b. A cap piece used in timbering. CF: lag.


In the coke-products industry, a laborer who lifts lids of charging holes of ovens and chips carbon from edges of holes, using bars with hook-and-chisel ends. Syn: charger.


Scot. In mine haulage, a command to stop.


a. Scot. The line, direction, or bearing; as of a vein, lode, or fault.

b. Pass-by; shunt; a storage or bypass arrangement in haulage track. Also spelled lye. c. To become quiet or inactive; said of a mine that is idle.


An orthorhombic mineral, Ca (sub 2) (UO (sub 2) )(CO (sub 3) ) (sub 3) .11H (sub 2) O ; olive-green; forms soft, scaly, or granular crystalline aggregates with one cleavage. Syn: uranothallite.


Right to legal claim on goods or property.

liesegang banding

Banding in color and composition of ores caused by diffusion.


See: ilvaite.


A slide wire or cable extending from a work platform in a drill tripod or derrick at an oblique angle downward to an anchor on the ground, which the derrick or tripod worker could grasp and use when sliding to safety in an emergency.

life of mine

The time in which, through the employment of the available capital, the ore reserves--or such reasonable extension of the ore reserves as conservative geological analysis may justify--will be extracted.

life of property

Theoretically, the mineral or coal reserves divided by the actual or projected average annual production.


a. The vertical height traveled by a cage in a shaft.

b. The distance between the first level and the surface or between any two levels. c. Any of the various gangways from which coal is raised at a slope colliery. d. A certain thickness of coal worked in one operation. e. To break up, bench, or blast coal from the bottom of the seam upward. f. The plane approx. parallel with the floor of the quarry, along which the stone is usually split in quarrying. g. The quantity of ore between one haulage level and the next above or below. h. A step or bench in a multiple layer excavation. i. The amount a bit is raised off the bottom of a drill hole by excessive pressure created by pump surges or the forcing of too great a volume of circulation fluid through the bit. j. In churn drilling, the vertical movement of the drill tools while drilling. k. In pumping, the difference in the elevation between the surface of the liquid being pumped and the elevation at which the pump stands or the elevation at which the liquid is discharged. l. A certain vertical thickness of coal seams and measures, having considerable inclination, between or in which the workings are being carried on to the rise, all the coal being raised from one shaft bottom. m. The upheaval of the floor in coal mines. See also: creep. n. The extraction of a coal pillar in lifts or slices. See also: jud.


a. In mining, a shothole drilled near the floor when tunneling and fired subsequently to the cut and relief holes.

b. See: core lifter. c. In ore grinding, a projection, rib or wave profile on the horizontal liners (body liners) of a ball, tube, or rod mill, designed to aid the crop load in the mill to rise. In a drum-washer or dense-medium separator, a perforated plate, projecting radially inward from the circumference of a horizontal cylindrical vessel, used to stir, lift, or remove material.

lifter holes

Shotholes drilled along the floor of a tunnel for lifting the rock to floor level. They are fired after the cut holes, or by delay detonators in the round.


See: lifter holes.

lifter spring

See: core lifter.

lift gate

A lock gate that is raised vertically to open.

lift hammer

See: tilt hammer.


Scot. Drawing hutches or cars out of the working places into the main roads.

lifting block

An arrangement of pulleys and rope that enables heavy weights to be lifted with least effort.

lifting capacity

a. The weight that the hydraulic cylinders in the swivel head of a diamond drill can raise or lift.

b. See: drill capacity.

lifting guard

Fencing placed around the mouth of a shaft, and lifted out of the way by the ascending cage.

lifting magnet

An electromagnet that is hung from a crane and used instead of a hook for lifting iron or steel components.

lifting set

A series of pumps or sets of pumps by which water is lifted from the mine in successive stages. See: lift.

lifting wicket

S. of Wales. See: lifting guard.

lift joint

A horizontal tension fracture observed in massive rocks, such as granite; thought to originate from the removal of load in quarrying. CF: sheeting.

lift pump

A pump for lifting to its own level, as distinguished from a force pump. A suction pump. Also called bucket pump. See also: suction head.

light alloys

The general term for alloys of aluminum and magnesium used for structural purposes.

light blasting

Includes loosening up of shallow or small outcrops of rock and breaking boulders. It may constitute the entire job, be done in connection with dirt excavation, or follow heavy blasting that has failed to cut gradelines or slope lines, or has left chunks too large to load.

light burden

See: burden.


See: leucocratic.


A peculiar brightening of molten silver, indicating that maximum purity has been attained. Occurs in cupellation.

light-extinction method

See: turbidimeter.

light figure

The visible geometric figure observed when an etched flat surface of quartz is placed over a pinhole-focused light source.


In metallurgy, annealing.


Person who uses an electric extension light as an aid in detecting blisters and flaws in the inside of green pipe.

light mineral

a. A rock-forming mineral of a detrital sedimentary rock, having a specific gravity lower than a standard (usually 2.85); e.g., quartz, feldspar, calcite, dolomite, muscovite, feldspathoids. CF: heavy mineral.

b. A light-colored mineral.

lightning explosion

Eng. An explosion of combustible gases caused by electric current, during a thunderstorm, entering a mine and igniting the gas.

lightning gap

A lightning gap is a break about 6 ft (1.8 m) long made at the mine entrance in blasting circuits, used in firing blasts from the outside, to prevent lightning discharges from following the circuits into the mine.

lightning protection

A system to enable high electrical discharge from the atmosphere to be conducted safely to earth by one or more conductors. The provision is very important in the case of mine explosive stores and also headgears, tower winders, and chimneys.

lightning tube

See: fulgurite.

light railway

A railway built to narrow gage.

light red silver ore

See: proustite.

light ruby ore

See: proustite.

light ruby silver

See: proustite.

light water

Ordinary water, H (sub 2) O , as distinguished from heavy water, D (sub 2) O , D being the symbol for deuterium (heavy hydrogen or hydrogen 2).

lightweight aggregate

An aggregate with a relatively low specific gravity; e.g., pumice, volcanic cinders, expanded shale, foamed slag, or expanded perlite or vermiculite. CF: aggregate.

lightweight concrete

A concrete made with lightweight aggregate.

light-yellow heat

A division of the color scale, generally given as about 2,400 degrees F (1,316 degrees C).

lignin sulfonic acids

Chemicals produced during the sulfite treatment of wood pulps. Of interest in flotation process as a deflocculating agent and protective colloid.


a. A brownish-black coal in which the alteration of vegetal material has proceeded further than in peat but not so far as subbituminous coal.

b. Coal of low rank with a high inherent moisture and volatile matter; in this general sense, lignite may be subdivided into black lignite, brown lignite, and brown coal.

lignite A

The rank of coal, within the lignitic class of Classification D 388, such that, on the moist, mineral-matter-free basis, the gross calorific value of the coal in British thermal units per pound is equal to greater than 6,300 (14.65 MJ/kg but less than 8,300 (19.31 MJ/kg), and the coal is nonagglomerating.

lignite B

The rank of coal, within the lignitic class of Classification D 388, such that, on the moist, mineral-matter-free basis, the gross calorific value of the coal in British thermal units per pound is less than 6,300 (14.65 MJ/kg), and the coal is nonagglomerating.


Containing lignite.

lignitic coal

See: subbituminous coal.


An apple-green variety of titanite.


An orthorhombic mineral, Cu (sub 3) (NO (sub 3) )(OH) (sub 5) .2H (sub 2) O ; sky blue; at Likasi, Kutanga, Zaire.


Said of a rock, lode, or belt of ground that gives indications of containing valuable minerals. Syn: kindly. CF: hungry.


Eng. Greenish-gray shale; weathering yellow; Wenlock Limestone, Dudley.


An orthorhombic mineral, Pb (sub 3) Bi (sub 2) S (sub 6) .

Lilly controller

A controller used on both steam and electric winding engines that protects against overspeed, overwind, too rapid acceleration, delayed retardation, and against starting in the wrong direction. It also gives warning of overspeed and indicates by a bell signal when retardation should commence.


a. That area of a fold between adjacent fold hinges. It generally has a greater radius of curvature than the hinge region and may be planar. Syn: flank. Obsolete syn. shank.

b. The graduated margin of an arc or circle in an instrument for measuring angles, such as the part of a marine sextant carrying the altitude scale. c. The graduated staff of a leveling rod. See also: tribrach.


a. Calcium oxide, CaO; specif. quicklime and hydraulic lime. The term is used loosely for calcium hydroxide (as in hydrated lime) and incorrectly for calcium carbonate (as in agricultural lime).

b. A cubic mineral, CaO. c. A term commonly misused for calcium in such deplorable expressions as carbonate of lime or lime feldspar. d. A limestone. The term is sometimes used by drillers for any rock consisting predominantly of calcium carbonate.

lime boil

A reaction in an open-hearth furnace caused by the decomposition of limestone and the escape of the carbon dioxide gas. This reaction begins before the ore boil is completed. See also: ore boil.


Person who burns limestone or shells to make lime.

lime feldspar

Misnomer for calcium feldspar. See also: anorthite.

lime mica

See: margarite.

lime mortar

A mortar in which lime is used as a binding agent instead of cement.

lime pan

a. A playa with a smooth, hard surface of calcium carbonate, commonly tufa.

b. A type of hardpan cemented chiefly with calcium carbonate. Also spelled limepan.

lime pit

a. A limestone quarry.

b. A pit where lime is made.

lime rock

A term used in the Southeastern United States (esp. Florida and Georgia) for an unconsolidated or partly consolidated form of limestone, usually containing shells or shell fragments, with a varying percentage of silica. It hardens on exposure and is sometimes used as road metal. Also spelled limerock.

lime set

An infusible slag, too high in lime, in an iron blast furnace.

lime shells

Scot. Calcined limestone.

lime-silicate rock

See: calc-silicate rock.

lime slaker

Person who mixes lime and water in rotary slaker or open batch tank to make milk of lime (slaked lime). Also called lime mixer; milk-of-lime slaker; slaker.

lime-soda sinter process

A process for manufacturing alumina, Al (sub 2) O (sub 3) . The raw material, such as clay or anorthosite, is sintered with limestone and soda ash to form sodium aluminate and calcium silicate. This sinter is then leached with water, caustic soda solution, or sodium aluminate liquor to dissolve the soluble sodium aluminate. The resulting slurry is then filtered, and the liquor is decomposed as in the Bayer process or is treated with carbon dioxide to precipitate hydrated alumina. When operated in conjunction with the Bayer process to recover alumina and soda from red mud, it is called the combination process.


a. A sedimentary rock consisting chiefly (more than 50% by weight or by areal percentages under the microscope) of calcium carbonate, primarily in the form of the mineral calcite, and with or without magnesium carbonate; specif. a carbonate sedimentary rock containing more than 95% calcite and less than 5% dolomite. Common minor constituents include silica (chalcedony), feldspar, clays, pyrite, and siderite. Limestones are formed by either organic or inorganic processes, and may be detrital, chemical, oolitic, earthy, crystalline, or recrystallized; many are highly fossiliferous and clearly represent ancient shell banks or coral reefs. Limestones include chalk, calcarenite, coquina, and travertine, and they effervesce freely with any common acid. Abbrev. ls.

b. A general term used commercially (in the manufacture of lime) for a class of rocks containing at least 80% of the carbonates of calcium or magnesium and which, when calcined, gives a product that slakes upon the addition of water.

limestone dust

Dust prepared by grinding limestone; used to dilute the coal dust accumulation in a mine so that the dust does not form explosive mixtures with air.


Natural water with large amounts of dissolved calcium bicarbonate or calcium sulfate.

limit charge

A charge that gives a complete loosening of the rock without throwing it excessively.

limiting creep stress

A somewhat loose term used to denote the maximum stress at which a material will not creep by more than a certain amount within the working life of the part. It is also used in some short-time creep tests; e.g., the Hatfield time yield.

limiting current density

The maximum current density that can be used to get a desired electrode reaction without undue interference, such as may come from polarization.

limiting gradient

The maximum railway gradient that can be climbed without the help of a second power unit. Syn: ruling gradient.

limiting mixture

The mixture of coal and rock dusts that will not permit the propagation of an explosion.

limit line

The line joining the coal face underground and the surface limit of draw; the boundary of a mine.

limit of draw

The point on the surface beyond which no movement occurs.

limit of proportionality

The point on a stress-strain curve at which the strain ceases to be proportional to the stress. Its position varies with the sensitivity of the extensometer used in measuring the strain.

limits of flammability

a. Extreme concentration limits of a combustible in an oxidant through which a flame, once initiated, will continue propagating at a specified temperature and pressure.

b. Usually expressed as the limiting percentages of methane in air, beyond which the mixture is no longer flammable. The lowest percentage of methane in air that yields a flammable mixture is called the lower limit of flammability, and the highest percentage of methane in air to yield a similar mixture is called the higher limit of flammability. These limiting percentages depend on a number of factors, such as the initial temperature and pressure; whether the mixture is at rest or moving; the manner in which the mixture is confined, etc. With methane mixtures at ordinary mine pressures and temperatures, the widest limits of flammability are (1) lower limit of flammability about 5.4% of methane in air; (2) higher limit of flammability about 14.8% of methane in air. See also: methane.

limit switch

a. A device fitted to an electrically driven hoist or winding engine that becomes effective at the end of a wind to prevent the cage overwinding or underwinding.

b. A control to limit some function.


a. Said of coal deposits formed inland in freshwater basins, peat bogs, or swamps, as opposed to paralic coal deposits. CF: paralic.

b. Said of peat formed beneath a body of standing water. Its organic material is mainly planktonic.

limnic coal basin

A coal basin formed inland from the seacoasts, as opposed to a paralic coal basin.


See: bog iron; bog iron ore.


A rock composed of cryptocrystalline and amorphous hydrated iron oxyhydroxides, generally predominantly goethite with or without adsorbed water, but also akaganeite, feroxyhyte, or lepidocrocite; may be yellow, red, brown, or black; hardness variable; an oxidation product of iron (rust) or iron-bearing minerals and may be pseudomorphous after them; as a precipitate, both inorganic and biogenic, in bogs, lakes, springs, or marine deposits; and as a variety of stalactitic, reniform, botryoidal, or mammillary deposits. It colors many yellow clays and soils and is a minor ore of iron. See also: iron ore; brown hematite; brown umber. CF: bog iron ore. Syn: brown iron ore; brown hematite; brown ocher; meadow ore; yellow ocher.


Consisting of or resembling limonite.


A metasomatic rock found at the contact of calcareous rocks with intruded granite and consisting of more than 50% axinite. Other minerals include diopside, actinolite, zoisite, albite, and quartz. See also: calc-silicate hornfels.


A monoclinic mineral, 2[PbCu(SO (sub 4) )(OH) (sub 2) ] ; azure blue; in oxidized zones of lead, copper, and silver deposits.