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

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pea coal

In anthracite only, coal small enough to pass through a mesh 3/4 to 1/2 in (1.9 to 1.3 cm) square, but too large to pass through a 3/8-in (9.5-mm) mesh. When buckwheat coal is made, the size marketed as pea is sometimes larger than the above; known also as No. 6 coal. See also: anthracite coal sizes.

peacock coal

Iridescent coal, the iridescence of which is due to a thin film of some substance deposited on the surface of the coal along minute cracks.

peacock ore

Informal name for an iridescent copper mineral having a lustrous, tarnished surface exhibiting variegated colors, such as chalcopyrite and esp. bornite. Also called peacock copper. See also: bornite.

pea gravel

Clean gravel, the particles of which are similar in size to that of peas.

pea grit

The term pea grit has been used for a coarse pisolitic limestone. Such usage should be discontinued; it is erroneous. The term grit should be reserved for a coarse-grained sandstone composed of angular particles.

pea iron ore

A variety of pisolitic limonite or "bean ore" occurring in small, rounded grains or masses. Syn: pea ore.

peak load

Maximum permitted power draft from an electric supply main.

peak loading

The maximum number of tons of a specified material to be carried by a conveyor per minute in a specified period of time.

peak particle velocity

The maximum rate of change of ground displacement with time.

peak stope

Flat stope advanced (overhand if deposit is inclined) in slanted steps, each flat forming a separate working place.

pea ore

a. Eng. Rounded grains of hydrated peroxide of iron, or silicate of iron, commonly found in cavities of Jurassic limestone. See also: bean ore.

b. A variety of pisolitic limonite or bean ore occurring in small, rounded grains or masses. Syn: pea iron ore.


A monoclinic mineral, Ag (sub 16) As (sub 2) S (sub 11) , having copper as an apparent necessary minor component; forms pseudorhombohedral tabular crystals or may be massive; metallic black; brittle; in low-to moderate-temperature silver and base-metal ores.


A dense spherical calcareous concretion, usually white or light-colored, consisting of occasional layers of conchiolin and predominant nacrous layers of aragonite (or rarely calcite); deposited concentrically about a foreign particle within or beneath the mantle of various marine and freshwater mollusks; occurs either free from or attached to the shell.

pearl ash

Potassium carbonate, K (sub 2) CO (sub 3) ; esp., an impure product obtained by partial purification of potash from wood ashes.


The lamellar mixture of ferrite and cementite in the microstructure of slowly cooled iron-carbon base alloys occurring normally as a principal constituent of both steel and cast iron.

pearlite iron

a. In general, pearlite iron is gray cast iron consisting of graphite in a matrix of pearlite; i.e., without free ferrite.

b. In particular, pearlite iron is a German proprietary name denoting an iron of low silicon content, which is caused to solidify gray by the use of heated molds.

pearl mica

See: margarite.

pearl opal

See: cacholong.

pearl sinter

A variety of opal. Syn: fiorite. See also: siliceous sinter.

pearl spar

Dolomite occurring in rhombohedrons having a pearly luster. Syn: ankerite; bitter spar. See also: dolomite.


See: perlite.


Applied to minerals having a luster like a pearl; e.g., talc, brucite, and stilbite. See also: nacre. CF: vitreous.


See: pisolite.


There are two types of peat, low moor (Flachmoor) and high moor (Hochmoor) peat. Low moor peat is the most common starting material in coal genesis. It therefore constitutes a caustobiolith of low diagenetic degree. Peat is formed in marshes and swamps from the dead, and partly decomposed remains of the marsh vegetation. Stagnant ground water is necessary for peat formation to protect the residual plant material from decay. Peat has a yellowish brown to brownish black color, is generally of the fibrous consistency, and can be either plastic or friable; in its natural state it can be cut; further, it has a very high moisture content (above 75%, generally above 90%). It can be distinguished from brown coal by the fact that the greater part of its moisture content can be squeezed out by pressure (e.g., in the hand). Peat also contains more plant material in a reasonably good state of preservation than brown coal. Individual plant elements, such as roots, stems, leaves, and seeds, can commonly be seen in it with the unaided eye. Failing that, treatment of peat with dilute alkali will make visible many of these plant tissues. Further, peat is richer in cellulose than brown coal (reaction with Fehling's solution). Unlike brown coal, peat still contains cellulose, protected by lignin or cutin, which gives a reaction with chlorzinc iodide. Correspondingly, peat shows under the microscope tissues that have not undergone either lignification, suberinization, or cutinization; this is not the case in brown coal. The reflectance of peat is low (about 0.3%). Microscopic examination is best undertaken with transmitted light.

peat bed

An accumulation of peat.

peat blasting

A method enabling a road to be built across peat deposits. Hard filling is first dumped over the route to a height equal to the ascertained depth of the peat, into which blasting charges are inserted. By the action of blasting, the peat is displaced outwards and the hard fillings sink into place and can then be consolidated.

peat bog

A bog containing peat; an accumulation of peat.

peat gel

See: dopplerite.

peat hag

A pit or quag formed by digging out peat.

peat machine

A machine for grinding and briquetting peat.


A digger or seller of peat.

peat moss

Any moss from which peat has formed or may form.

peat press

A machine for making bricks of peat fuel.

peat spade

A spade with an L-shaped blade for cutting out peat in blocks.

peat-to-anthracite theory

The theory that there were progressive stages in the conversion of vegetable matter into the various grades of coal of the Carboniferous system. Thus, peat forms at an early stage in coal formation and lignite at an intermediate stage, and by further compression and alteration, bituminous and anthracite coals were formed. See also: Hilt's law.


a. A general term for a small, roundish, esp. waterworn stone; specif. a rock fragment larger than a granule and smaller than a cobble, having a diameter in the range of 4 to 64 mm (-2 to -6 phi units, or a size between that of a small pea and that of a tennis ball), being somewhat rounded or otherwise modified by abrasion in the course of transport. In Great Britain, the range of 10 to 50 mm has been used. The term has been used to include fragments of cobble size; it is frequently used in the plural as a syn. of "gravel". Syn: pebblestone.

b. Transparent and colorless quartz crystal, such as Brazilian pebble. c. Grinding media for ball or semi-autogeneous mills. As a rule, these are either hard-flint pebbles or hard-burned, white porcelain balls.

pebble armor

A concentration of pebbles coating a desert area. The pebbles are usually the residual product of wind erosion and are closely fitted together so as to cover the surface in the manner of a mosaic. Also called desert pavement. See also: lag gravel.

pebble dike

a. A clastic dike composed largely of pebbles.

b. A tabular body containing sedimentary fragments in an igneous matrix, as from the Tintic district in Utah; e.g., one whose fragments were broken from underlying rocks by gaseous or aqueous fluids of magmatic origin and injected upward into country rock, becoming rounded owing to the milling and/or corrosive action of the hydrothermal fluids.

pebble gravel

An unconsolidated deposit consisting mainly of pebbles.

pebble jack

Sphalerite in small crystals or pebblelike grains not attached to rock, but found in clay in wall rock cavities.

pebble mill

Horizontally mounted cylindrical mill, charged with flints or selected lumps of ore or rock. Usually long and high discharge. See also: ball mill.

pebble phosphate

A secondary phosphorite of either residual or transported origin, consisting of pellets, pebbles, and nodules of phosphatic material mixed with sand and clay, such as occurs in Florida; e.g., land-pebble phosphate and river-pebble phosphate. See also: phosphorite.

pebble powder

A gunpowder or black powder pressed and cut into large cubical grains so as to make it slow burning.


See: pebble.


A fernlike tree of the coal forest, with small ovate pinnules that are attached to the pinnate axis by their whole breadth.

Pecos ore

a. A gossan containing lead and silver.

b. Tasmania. A yellowish, earthy mixture of oxides of iron, lead, and antimony containing silver; mostly massicot.


A triclinic mineral, NaCa (sub 2) Si (sub 3) O (sub 8) (OH) ; isomorphous with serandite; forms compact masses or fibers; commonly associated with zeolites in cavities and veins in mafic rocks.


Soil enriched in alumina and iron in regions of high temperature and humid climate that are marked by forest cover. CF: pedocal.


A relatively slender neck or column of rock capped by a wider mass of rock and produced by undercutting as a result of wind abrasion (as in the Southwestern United States.) or by differential weathering. See also: pedestal rock. Syn: rock pedestal.

pedestal boulder

a. A class of blocks perched on pedestals of limestone.

b. Isolated masses or rock above and resting on a smaller base or pedestal.

pedestal rock

An isolated, residual or erosional mass of rock supported by or balanced on a pedestal. The term is also applied to the entire feature. See also: pedestal boulder.

pedestrian-controlled dumper

A small dumper controlled by a person walking alongside it. Syn: power barrow.


A broad, gently sloping rock-floored erosion surface or plain of low relief, typically developed by running water in an arid or semiarid region at the base of an abrupt and receding mountain front or plateau escarpment; underlain by bedrock that may be bare, but is more often partly mantled with a thin discontinuous veneer of alluvium derived from the upland masses and in transit across the surface.


The process of pediment formation.

pediment pass

A narrow, flat, rock-floored tongue extending upslope from the main pediment and penetrating a mountain sufficiently to meet another pediment slope extending into the mountain from the other side.


A crystal form consisting of a single crystal face.


Broad, rock-cut, thinly alluviated surface formed by the coalescence of adjacent pediments and desert domes.

pedis possessio

The actual possession of a piece of mineral land to the extent needed to give the locator room to work and to prevent probable breaches of the peace, but not necessarily to the extent of a mining claim.


Soil enriched in calcium carbonate, accumulating in regions of low temperature, low rainfall, and prairie vegetation. CF: pedalfer.


The formation of soil from parent material.

pedogeochemical prospecting

Synonymous with geochemical soil survey.

pedologic horizon

See: soil horizon.


The science that treats soils, their origin, character, and utilization.


A pocket-size instrument that registers the number of steps taken by the person carrying it.


The part of the Earth in which soil-forming processes occur.


a. One of a set of blades that picks up and channels water moved outward by the impeller of a centrifugal pump.

b. An iron implement with a flattened end and ring handle, which is used by a baller in placing blooms, ingots, etc., in a reheating furnace. c. See: calk.

Peerless explosive

High explosive; used in mines.


a. A surveyor's mark.

b. To mark out a miner's claim at the four corners by pegs bearing the claimant's name. Sometimes used as "peg out."

peg adjustment

The adjustment of a spirit-leveling instrument of the dumpy-level type in which the line of collimation is made parallel with the axis of the spirit level by means of two stable marks (pegs) the length of one instrument sight apart.


An abrupt change or sharp bend in the course of a borehole. Also called dogleg.


An exceptionally coarse-grained igneous rock, with interlocking crystals, usually found as irregular dikes, lenses, or veins, esp. at the margins of batholiths. Most grains are 1 cm or more in diameter. Although pegmatites having gross compositions similar to other rock types are known, their composition is generally that of granite; the composition may be simple or complex and may include rare minerals rich in such elements as lithium, boron, fluorine, niobium, tantalum, uranium, and rare earths. Pegmatites represent the last and most hydrous portion of a magma to crystallize and hence contain high concentrations of minerals present only in trace amounts in granitic rocks. Adj: pegmatitic. Syn: giant granite. CF: symplectite.


a. Said of the texture of an exceptionally coarsely crystalline igneous rock.

b. Occurring in, pertaining to, or composed of pegmatite. Syn: pegmatoid.

pegmatitic stage

a. A final stage in the normal sequence of crystallization of a magma at which the residual fluid is sufficiently enriched in volatile materials to permit the formation of coarse-grained rocks (pegmatite) more or less equivalent in composition to the parent rock. CF: orthomagmatic stage.

b. The late stages of magma crystallization in S-type, 2-mica granites.


The process of formation of, introduction of, or replacement by pegmatite.


See: pegmatitic.


See: orthoclase.

peg point

A pointed bar in a slide clamp. Used to brace a machine during work.

peg structure

A structure characterized by tiny peg-shaped cavities, some with intricate profiles, penetrating the interior of crystals; typical of melilite.

Pehrson-Prentice process

A method of producing steel direct from ore.

Peirce-Smith converter

A cylindrical-type converter having a basic (magnesite) lining; used for treating copper.

Peirce-Smith process

A basic converting process for copper matte in a magnesite-lined converter. The iron of the matte is fluxed by silica added before the process begins.

Peissenberg ram

See: ram scraper.


See: permissible exposure limit.

pelagic deposit or sediment

Deposit found in deep water far from shore and may be predominantly either organic or inorganic in origin. Such deposits are light colored, reddish or brown, fine grained, and generally contain some skeletal remains of plankton organisms. Those that contain less than about 30% of organic remains are called red clay; those that contain more than about 30% of organic remains are known as oozes.


A term applied to coal deposits formed from submerged forests and driftwood.

Pelatan-Clerici process

A continuous process of dissolving silver or gold in cyanide solution and simultaneously precipitating the precious metals with mercury in the same vessel, with an electrical current assisting precipitation.


An English term for a very hard, smooth compact sandstone with conchoidal fracture that occurs in coal measures.

Pele's hair

A natural spun glass formed by blowing-out during quiet fountaining of fluid lava, cascading lava falls, or turbulent flows, sometimes in association with Pele's tear pyroclast. A single strand, with a diameter of less than 1/2 mm, may be as long as 2 m. Etymol: Pele, Hawaiian goddess of fire.

Pele's tears

Small, solidified drops of volcanic glass behind which trail pendants of Pele's hair. They may be tear shaped, spherical, or nearly cylindrical. Etymol: Pele, Hawaiian goddess of fire.


a. A sediment or sedimentary rock composed of the finest detritus (clay- or mud-size particles); e.g., a mudstone, or a calcareous sediment composed of clay and minute particles of quartz. The term is equivalent to the Latin-derived term lutite.

b. A fine-grained sedimentary rock composed of more or less hydrated aluminum silicates with which are mingled small particles of various other minerals; an aluminous sediment. Etymol: Greek pelos, clay mud. See also: psammite; psephite. Also spelled pelyte.


a. Pertaining to or characteristic of pelite; esp. said of a sedimentary rock composed of clay, such as a pelitic tuff representing a consolidated volcanic ash consisting of clay-size particles.

b. Said of a metamorphic rock derived from a pelite; e.g., a pelitic hornfels or a pelitic schist, derived by metamorphism of an argillaceous or a fine-grained aluminous sediment.

pelitic gneiss

A gneiss derived from the metamorphism of argillaceous sediments.

pelitic hornfels

A fine-grained, nonfissile metamorphic rock derived from an argillaceous sediment. See also: hornfels.

pelitic schist

A schistose metamorphic rock derived from an argillaceous sediment. See also: schist.


A method in which finely divided material is rolled in a drum or on an inclined disk, so that the particles cling together and roll up into small, spherical pellets. The addition of a binder may be required to produce a pellet of acceptable mechanical strength.


A waterproof, free-running blasting agent. Pelletol is a high explosive, but is not considered cap sensitive and normally cannot be initiated with a cap, except under perfect confinement in small-diameter boreholes.

pellet powder

Black powder pressed into cylindrical pellets 2 in (5.1 cm) in length and varying from 1-1/4 to 2 in (3.2 to 5.1 cm) in diameter. Each pellet has a 3/8-in (9.5-mm) hole through its center to permit fuse insertion.

pellet texture

A concretionary texture characterized by minute pellets of colloidal or replacement origin and closely resembling oolites.

pell-mell structure

Coarse deposits of waterworn materials in which there is an absence of bedding.


A worker employed in a coal mine to take down pelt (shaly stone) from the roof of a narrow seam, to make enough height for a coal cutting machine.

Pelton wheel

An impulse water turbine with buckets bolted to its periphery, which are struck by a high velocity jet of water. This turbine is most efficient under a head of from 900 to 1,000 ft (274 to 305 m) or more. See also: impulse turbine.


See: pelite.


A large stone or boulder. Etymol: Spanish, "rock."


a. In connection with a contract for purchase of mineral concentrates by a custom smelter, a deduction from an agreed price for failure to reach an agreed assay value or to eliminate specified contaminants; charged at so much per unit of mineral or metal concerned.

b. In a construction contract, a penalty clause is one that imposes a penalty for failure to complete work to agreed time, specification, etc.

Penang tin

Pig tin of about 99.95% purity, obtained from the Penang Mines in Malaysia.

Penberthy anoloader

A simple powder loader with a high air velocity that is used in Canada in underground work for charging holes with a depth of up to 14 ft (4 m).

pencil-core bit

The very-thick-wall, medium-round nose bit that cuts a pencil-size core. The bit is essentially a noncoring bit, and in most instances no attempt is made to recover the very-small-diameter core as a sample. Syn: pencil-coring crown.

pencil-coring crown

See: pencil-core bit.

pencil ganister

A variety of ganister characterized by fine carbonaceous streaks or markings; so called from the likeness of these to pencil lines. The carbonaceous traces are often recognizable as roots and rootlets of plants.


Reduction in the fire face area of the brick, in which slag erosion at the joints is pronounced.

pencil mark

Aust. A thin bed of dark slate, about the thickness of the lead of a carpenter's pencil, that is parallel to the indicator. See also: indicator.

pencil ore

Hard, fibrous masses of hematite that can be split up into thin rods.

pencil stone

A compact pyrophyllite used for making slate pencils.

pencil structure

A very pronounced lineation, such as that produced by intersecting bedding and cleavage planes in slate.


See: roof pendant.


See: karpatite.


In mechanized mining, the arm that extends between the fulcrum jack and the swivel or angle trough or turn.

pendulum buffer

In Vermont, large wooden blocks covered with felt pads that are propelled back and forth by means of a crank and pitman. Used for polishing monumental stone.

pendulum mill

See: Griffin mill; Huntington mill.


Small folds and faults that form in sediments shortly after they are deposited, in igneous rocks as they solidify, and in metamorphic rocks as they recrystallize. �E ��[ � \ Z�/�� � ��DICTIONARY TERMS:peneplain A nearly horizontal surface of slight rel A nearly horizontal surface of slight relief and very gentle slopes, formed by the subaerial degradation of the land almost to baselevel; the penultimate state of the old age of the land produced by such degradation. By extension, such a surface uplifted to form a plateau and subjected to renewed degradation and dissection. See also: baseleveled plain.


The subaerial degradation of a region approx. to base level, forming a peneplain.

penetrating pulley

A pulley around which a wire cable runs in cutting marble. Its thickness is less than the diameter of the wire and consequently, it can follow the wire as the latter cuts into the stone.

penetration feed

See: feed rate.

penetration log

The penetration speed of a drill related to the size of the hole and bit, mud pressure, speed of rotation, weight on bit, etc. From the results, which are plotted as penetration curves, the thickness of coal and dirt bands in the borehole can be determined with reasonable accuracy.

penetration macadam

Screened gravel or crushed stone aggregate, bound by bituminous grouting, the binder being introduced after compaction of the aggregate.

penetration per blow

The distance a drive-type soil sampler, casing, drivepipe, pile, or penetrometer is driven into the formation being tested by each blow delivered by a specific-size drivehammer allowed to fall a specific distance.

penetration rate

The actual rate of penetration of drilling tools. See also: feed rate; drilling rate.

penetration resistance

a. The number of blows of a hammer of specified weight falling a given distance required to produce a given penetration into soil of a pile, casing, or sampling tube. Also called standard penetration resistance; proctor penetration resistance.

b. The unit load required to maintain constant rate of penetration into soil by a probe or instrument. c. The unit load required to produce a specified penetration into soil at a specified rate by a probe or instrument. For a proctor needle, the specified penetration is 2-1/2 in (6.35 cm) and the rate is 1/2 in/s (1.27 cm/s).

penetration resistance curve

The curve showing the relationship between the penetration resistance and the water content. Also called proctor penetration curve.

penetration speed

The speed at which a drill can cut through rock or other material. See also: overall drilling time.

penetration test

A test to determine the relative densities of noncohesive soils, sands, or silts; e.g., the standard penetration test that determines the number of blows required by a standard weight, when dropped from a standard height (30 in or 76.2 cm per blow), to drive a standard sampling spoon a standard penetration (12 in or 30.5 cm); or the dynamic penetration test, which determines the relative densities of successive layers by recording the penetration per blow or a specified number of blows. See also: cone penetration test.

penetration twin

A twin crystal in which two parts interpenetrate with each other and share a common volume. Syn: interpenetration twin. CF: contact twin.


An instrument to assess the strength of a coal seam, its relative workability, and the influence of roof pressure. See also: sounding; coal penetrometer.

pennant flag

Unproductive grit and sandstone between the Lower and Upper Coal Measures, South Wales and Bristol, England, coalfield. Largely quarried for paving and building. Also called pennan grit; pennant stone.


A monoclinic mineral, Mn (sub 5) Al(Si (sub 3) Al)O (sub 10) (OH) (sub 8); chlorite group; excellent cleavage with flexible laminae; commonly associated with manganese deposits.


A pseudotrigonal variety of clinochlore. See also: penninite.

Pennine system

Eng. The original and typical series of Carboniferous rocks, comprising the Upper Old Red Sandstone, the Mountain limestone, the Millstone grit, and the Coal Measures.


See: cribbing.

penning gate

Regulating device used to govern the draft of water from a dam; may incorporate arrangements for holding back sediment or floating detritus.


A green crystallized chlorite from the Penninic Alps. Composition essentially the same as that of clinochlore, (Mg,Fe (super 2+) ) (sub 5) Al(Si (sub 3) Al)O (sub 10) (OH) (sub 8) . See also: pennine.


A period of the Paleozoic Era (after the Mississippian and before the Permian), thought to have covered the span of time between 320 million years and 280 million years ago; also, the corresponding system of rocks. It is named after the state of Pennsylvania in which rocks of this age are widespread and yield much coal. It is the approximate equivalent of the Upper Carboniferous of European usage.


One-twentieth troy ounce (1.56 g). Used in the United States and in England for the valuation of gold, silver, and jewels. Abbrev.: dwt; pwt.


An isometric mineral, (Ni,Co,Cu)Se (sub 2) ; pyrite group; cubic cleavage; forms radiating columnar masses; occurs in Bolivian mines near Colquechaca. Formerly called blockite.


a. A sluice or gate for restraining, deviating, or otherwise regulating the flow of water, sewage, etc.; a floodgate.

b. The barrel of a wooden pump. c. A closed conduit for supplying water under pressure to a water wheel or turbine.


A polygon having five sides.


A triclinic mineral, MgSO (sub 4) .5H (sub 2) O ; chalcanthite group; highly soluble. Formerly called allenite.


A triclinic mineral, CaB (sub 2) O(OH) (sub 6) .2H (sub 2) O ; colorless; forms small anhedra at a skarn in the Ural Mountains, Russia.

pentasol xanthate

Collector agent use in flotation, in which the hydrocarbon group is crude and unfractionated amyl alcohol. Symbol, Z-6.


a. Having a valence of five.

b. Having five valences.

Pentelic marble

One of the most famous of ancient statuary marbles; from Mount Pentelicus, Greece.


See: penthrite.


Pentaerythritol tetranite. Used as an explosive. Syn: penthrit; niperyth.


a. A rock pillar left, or a heavy timber bulkhead placed, in the bottom of a two-or-more-compartment-deep shaft through which to sink it further. A small, auxilliary steam or air hoist, dumping apparatus, and pocket or bin are installed above the pentice; through an opening in it, sinking by short lifts is carried on while the shaft is in use above the pentice. Practiced in the Michigan copper country.

b. A cover, protection, or roof over a sinking shaft. The cover contains a trapdoor through which the rope and bowk pass. See also: Galloway stage. c. In shaft sinking, a solid rock pillar left in the bottom of the shaft for overhead protection of miners while the shaft is being extended by sinking.


a. An isometric mineral, (Fe,Ni) (sub 9) S (sub 8) ; octahedral parting; metallic; pale bronze-yellow; nonmagnetic; generally associated with pyrrhotite, less commonly associated with chalcopyrite in magmatic sulfide deposits; the principal sulfide ore of nickel.

b. The mineral group argentopentlandite, cobalt pentlandite, geffroyite, manganese-shadlunite, pentlandite, and shadlunite.


A mixture of PETN and TNT used primarily for boosters and cast primers; military grade pentolite is usually 50% of each ingredient by weight; commercial pentolite often has a lower PETN content.


The trough in which the penstock of a water wheel is placed.


a. The movable vertical post of an arrastre.

b. A prop, post, or stall. c. Mex. Helper; a common laborer.

pepper-and-salt texture

Said of disseminated ores, esp. with dark grains in a light matrix.


a. Liquefaction of a gel; deflocculation and dispersion of solids in a pulp; conversion of a substance to its colloidal state by subdivision.

b. A dispersion due to the addition of electrolytes or other chemical substances.


To bring into colloidal solution; to convert into a solution. Syn: deflocculate.


Said of igneous rocks in which the molecular proportion of alumina is less than that of soda and potash combined.


Said of igneous rocks in which the molecular proportion of alumina exceeds that of soda, potash, and lime combined.

percentage extraction

The proportion of a coal seam that is removed from a mine. The remainder may represent coal in pillars or coal that is too thin or inferior to mine or is lost in mining. Shallow coal mines working under townships, reservoirs, etc., may extract only about 50% of the entire seam, the remainder being left as pillars to protect the surface. Under favorable conditions, longwall conveyor mining may extract from 80% to 95% of the entire seam. With pillar methods of working, the extraction ranges from 50% to 90%, depending on local conditions.

percentage ore

N.S.W. In most cases, understood to be the percentage of the metallic element present in the ore.

percentage subsidence

The measured amount of subsidence expressed as a percentage of the thickness of coal extracted. See also: full subsidence.

percentage support

The percentage of the total wall area of a mine that will actually be covered by supports.


a. Any of various units of measure for stonework, (including 24-3/4 ft (super 3) (0.70 m (super 3) ) representing a pile 1 rod (5.0 m) long by 1 ft (0.3 m) by 1-1/2 ft (0.46 m); or 16-1/2 ft (super 3) (0.47 m (super 3) ); or 25 ft (super 3) (0.71 m (super 3) ).

b. A measure of length equal to 5-1/2 yd or 16-1/2 ft (5.0 m); a rod, or pole; also, a square rod (25.3 m (super 2) ).

perched ground water

Unconfined ground water separated from an underlying main body of ground water by an unsaturated zone.

perched water

See: perched ground water.

perched water table

The water table of a body of perched ground water. See: vertical sand drain. See also: water table.


a. In the leaching treatment of minerals, a process whereby a solvent flows gently upward or downward through a bed of ore-bearing material sufficiently coarse textured to permit this flow. See also: sand leaching.

b. Slow laminar movement of water through small openings within a porous material. Also used as a syn. of infiltration. Flow in large openings such as caves is not included. CF: infiltration.

percolation leaching

The selective removal of the metal values from a mineral by causing a suitable solvent or leaching agent to seep into and through a mass or pile of material containing the desired mineral.

percolation rate

The rate, expressed as either velocity or volume, at which water percolates through a porous medium.

percussion bit

A rock-drilling tool with chisellike cutting edges, which when driven by impacts against a rock surface, drills a hole by a chipping action.

percussion cap

See: detonator; primer.

percussion drill

a. Drill in which the drilling bit falls with force onto rock. Also, a pneumatic drill in which a piston delivers hammer blows rapidly on the drill shank. Syn: churn drill; cable-tool drill; percussion machine.

b. Sometimes limited to large blasthole drills of the percussion type.

percussion drilling

Act of using a percussion drill. See also: percussion drill.

percussion figure

A pattern of radiating lines produced on a section of a crystal by a blow from a sharp point.

percussion machine

See: percussion drill.

percussion powder

Powder so composed as to ignite by a slight percussion; fulminating powder.

percussion sieve

An apparatus in which material is sorted according to size. It consists essentially of superimposed, oppositely inclined sieves, both mechanically agitated by vertical lever and having water sluices.

percussion system

Applicable to drill machines and/or the methods used to drill boreholes by the chipping action of impacts delivered to a chisel-edged bit. See also: churn drill; percussion drill.

percussion table

Early form of shaking table. See also: concussion table; shaking table.

percussive boring

A system of boring using solid or hollow rods or ropes; may be used for exploratory drilling and for blasting purposes. See also: boring.

percussive drill

A pneumatic drill that is used widely in mining for exploration and for blasting purposes. See also: rock drill.

percussive drilling

a. A method of drilling whereby repeated blows are applied by the bit, which is repositioned by intermittent rotation.

b. A form of drilling in which the rock is penetrated by the repeated impact of a reciprocating drill tool.

percussive machine

Any of several types of machine, including heading machines, air picks, and the numerous types of percussive drills.

perfect-discharge elevator

In the so-called perfect-discharge elevator, there is an extra set of traction or sprocket wheels on the discharge side, so set that they bend the chains back under the head wheels. As a consequence, the discharging chute may be placed directly under the buckets. This elevator will also handle material that packs, and both types of gravity-discharge elevators may be run much slower than the centrifugal type.

perfect frame

A structural frame that is stable under loads imposed upon it from any direction, but which would become unstable if one of its members were removed or one of its fixed ends became hinged.

performance curve

Any curve used to show the relationship between properties of coal and results of a specific treatment.

perhydrous maceral

Maceral having a high hydrogen content, such as exinite and resinite.


A prefix meaning around or beyond.


A kind of provitrain in which the cellular structure is derived from cortical material. CF: suberain; xylain.


a. The micropetrological constituent, or marceral, of periblain. It consists of cortical tissue almost jellified in bulk, but still showing indications of cell structure under a microscope.

b. A distinction of telinite based on botanical origin (cortical tissue). CF: suberinite.


a. An isometric mineral, MgO; cubic cleavage; colorless to yellow or brown; may be strongly colored by inclusions; occurs in high-temperature metamorphic rocks derived from dolomite. Syn: periclasite.

b. The mineral group bunsenite, manganosite, monteponite, periclase, and wuestite.


See: periclase.


Said of strata and structures that dip radially outward from, or inward toward, a center, to form a dome or a basin. CF: quaquaversal; centroclinal.


a. A general term for a fold in which the dip of the beds has a central orientation; beds dipping away from a center form a dome, and beds dipping toward a center form a basin. The term is generally British in usage. See also: centrocline; dome; quaquaversal.

b. A variety of albite elongated in the direction of the b-axis and often twinned with this as the twinning axis. It occurs in veins as large milky-white opaque crystals. Pericline is probably an albitized oligoclase.

pericline twin

A twin crystal, in the monoclinic system, whose twinning axis is the orthoaxis of the crystal.


a. A transparent to translucent green gem variety of forsterite in the olivine group. Also spelled peridote. Syn: bastard emerald.

b. A yellowish-green or greenish-yellow variety of tourmaline, approaching olivine in color. It is used as a semiprecious stone. See also: olivine.


See: peridot.


A general term for a coarse-grained plutonic rock composed chiefly of olivine with or without other mafic minerals such as pyroxenes, amphiboles, or micas, and containing little or no feldspar. Accessory minerals of the spinel group are commonly present. Peridotite is commonly altered to serpentinite.

peridot of Ceylon

See: Ceylonese peridot; peridot.

perimeter blasting

A method of blasting in tunnels, drifts, and raises, designed to minimize overbreak and leave clean-cut solid walls. Holes in the outside row are loaded with very light, continuous explosive charges and are fired simultaneously, so that they shear from one hole to the other.

perimeter of airway

In mine ventilation, the linear distance in feet of the airway perimeter rubbing surface at right angles to the direction of the airstream.


A crystal of one species enclosing one of another species.


a. The geochronologic unit lower in rank than era and higher than epoch, during which the rocks of the corresponding system were formed. It is the fundamental unit of the worldwide geologic time scale.

b. A term used informally to designate a length of geologic time; e.g., glacial period. c. The interval of time required for the completion of a cyclic motion or recurring event, such as the time between two consecutive like phases of the tide or a current. d. The duration of one complete cycle of a periodic function; the reciprocal of the frequency of such a function. The independent variable is limited to time. e. The elements between an alkali metal and the rare gas of next highest atomic number, inclusive, occupying one (a short period) horizontal row or two (a long period) horizontal rows in the periodic table. f. The time required for the power level of a reactor to change by the factor 2.718, which is known as e.

periodic law

The physical and chemical properties of the elements depend on the structure of their atoms and are for the most part periodic functions of the atomic number. See also: periodic table.

periodic reverse

Pertains to periodic change in the direction of flow of the current in electrolysis. It applies to the process and also to the machine that controls the time for both directions. Symbol, PR.

periodic table

An arrangement of elements based on the periodic law and proposed in various forms that are usually either short with only short periods (as in Mendeleev's original table) or long with long as well as short periods (as in most modern tables). See also: periodic law.

peripheral fault

A fault along the perimeter of a geologically elevated or depressed region.

peripheral speed

The distance a given point on the perimeter of a rotating circular object travels, expressed in feet or meters per second; sometimes incorrectly called lineal travel by some drillers. Syn: surface speed.

peripheral-turbine pump

This pump--sometimes called a regenerative pump--is classified with centrifugal pumps, but is designed to develop several times the head obtained from a centrifugal pump having the same-diameter impeller and the same speed. The maximum head developed does not have the same relation to the impeller diameter and speed of the centrifugal pump; it involves size and spacing of the impeller vanes, fluid channels, and other factors.

peripheral ventilation

A mine ventilation system in which the upcast shaft for taking air out of a mine is situated at the limits of the mining field or away from the downcast shaft. Also called transverse or one-way ventilation. Syn: transverse ventilation.


Said of an isothermal reversible reaction in a crystallizing melt or magma in which a liquid phase reacts with a solid phase to produce another solid phase on cooling.


a. A siliceous volcanic glass having numerous concentric spherical cracks that give rise to an onion-skin structure. Most perlite has a higher water content than obsidian. When perlite is heated to the softening point, it expands, or pops to form a light fluffy material similar to pumice. It is used as lightweight aggregate in concrete, as insulation for liquid fuels, and in potting soils.

b. A pearly volcanic glass.


a. Said of the texture of a glassy igneous rock that has cracked owing to contraction during cooling, the cracks forming small spheruloids. It is generally confined to natural glass, but occasionally found in quartz and other noncleavable minerals and as a relict structure in devitrified rocks.

b. Pertaining to or characteristic of perlite.


A permanently frozen layer of soil or subsoil, or even bedrock, which occurs to variable depths below the Earth's surface in arctic or subarctic regions. It underlies about one-fifth of the world's land area.

permafrost drilling

a. Boreholes drilled in subsoil and rocks in which the contained water is permanently frozen.

b. Holes drilled into perenially frozen ground that may be superficial unconsolidated material, bedrock, and ice. When no ice is present, it is called dry permafrost.


An iron-nickel alloy with high magnetic permeability.

permanent adjustment

The adjustment of a surveying instrument that is made infrequently and not at each setup. See also: temporary adjustment.

permanent expansion

Increase in bulk volume as a result of decrease in specific gravity.

permanent hardness

Hardness of water that cannot be removed by boiling. Opposite of temporary hardness.

permanent hard water

Hard water that cannot be softened by boiling; water containing magnesium sulfate or calcium sulfate.

permanent magnetism

Magnetic property of a substance maintained without external excitation.

permanent monument

A monument of a lasting character for marking a mining claim. It may be a mountain, hill, ridge, hogback, butte, canyon, gulch, river, stream, waterfall, cascade, lake, inlet, bay, arm of the sea, stake, post, monument of stone or boulders, shafts, drifts, tunnels, open cuts, or well-known adjoining patented claims.

permanent pump

A permanent main pump is one on which a mine depends for the final disposal of its drainage. As it is usually not moved during the life of the mine, its location, installation, and design require careful consideration. A permanent main pump may discharge on the surface, into an underground sump, or into some other part of a mine.

permanent set

The amount of permanent deformation of a material that has been stressed beyond its elastic limit.

permanent shaft support

After a shaft has been sunk to a certain depth, the final or permanent lining is inserted. This may consist of: brick walling; concrete blocks shaped to the curvature of the shaft; concrete lining put in liquid form behind shuttering; brick coffering; and cast-iron tubbing. The permanent lining is generally built up in sections, during which operation the temporary lining (such as skeleton tubbing) is removed. Concrete is now widely used as a permanent shaft support. See also: brick walling; lining; steel rectangular shaft supports.

permanent way

The completed assembly of rails, sleepers, fixings, and ballast forming the finished track for a railway.


A salt of permanganic acid of the type, MnO (sub 4) ; dark purple; good oxidizing agent; often used as a disinfectant.


a. The permeability (or perviousness) of rock is its capacity for transmitting a fluid. Degree of permeability depends upon the size and shape of the pores, the size and shape of their interconnections, and the extent of the latter. It is measured by the rate at which a fluid of standard viscosity can move a given distance through a given interval of time. The unit of permeability is the darcy. See also: millidarcy; coefficient of permeability.

b. In geophysics, the ratio of the magnetic induction to the magnetic intensity in the same region. In paramagnetic matter, the permeability is nearly independent of the magnetic intensity; in a vacuum, it is strictly so. But in ferromagnetic matter, the relationship is definite only under fully specified conditions. c. See: coefficient of permeability. d. In magnetism, a general term used to express various relationships between magnetic induction and magnetizing forces. These relationships are either absolute permeability, which is the quotient of a change in magnetic induction divided by the corresponding change in magnetizing force, or specific (relative) permeability, the ratio of the absolute permeability to the permeability of free space. e. In founding, the characteristics of molding materials which permit gases to pass through them. Permeability number is deteremined by a standard test. f. In powder metallurgy, a property measured as the rate of passage under specified conditions of a liquid or gas through a compact.


Pertaining to a rock or soil having a texture that permits passage of liquids or gases under the pressure ordinarily found in earth materials. Syn: pervious.


An instrument for measuring permeability.


A process of fossilization wherein the original hard parts of an animal have additional mineral material deposited in their pore spaces.


a. Means completely assembled and conforming in every respect with the design formally approved by the U.S. Mine Safety and Health Administration for use in gassy and dusty mines.

b. A machine or explosive is said to be permissible when it has been approved by the U.S. Mine Safety and Health Administration for use underground under prescribed conditions. All flameproof machinery is not permissible, but all permissible machinery is flameproof. c. A low-flame explosive used in gassy and dusty coal mines.

permissible blasting device

Any device, other than explosives, for breaking down coal that is approved by the U.S. Mine Safety and Health Administration.

permissible blasting unit

An electrical device for firing blasts, approved by the U.S. Mine Safety and Health Administration.

permissible dustiness

See: dust-free conditions.

permissible explosive

Explosive that has been tested for safety in handling and approved for use in mines by the U.S. Mine Safety and Health Administration.

permissible exposure limit

An exposure limit published and enforced by the U.S. Occupational Safety and Health Administration (OSHA) as a legal standard.

permissible hydraulic fluid

Any of several commercially available, fire-resistant fluids that are water-in-oil emulsions and can be substituted for flammable hydraulic fluids by users of large machinery, whether the equipment is operated underground or on the surface.

permissible lamp

Any electric or flame safety lamp that is similar in all respects to a lamp tested and approved by the U.S. Mine Safety and Health Administration.

permissible machine

Any drill, mining machine, loading machine, conveyor, or locomotive that is similar in all respects to machines tested and approved by the U.S. Mine Safety and Health Administration for use in gassy mines.

permissible mine equipment

Equipment that is formally approved by the U.S. Mine Safety and Health Administration after having passed the inspections, the explosion tests, and other requirements specified by the Administration. (All equipment so approved must carry the official approval plate required as identification for permissible equipment.)

permissible mine locomotive

See: electric permissible mine locomotive.

permissible motor

A motor the same in all respects as a sample motor that has passed certain tests made by the U.S. Mine Safety and Health Administration and installed and used in accordance with the conditions prescribed by the Administration. See also: explosion-proof motor.

permissible velocity

The highest velocity at which water may be carried safely in a canal or other conduit; the highest velocity throughout a substantial length of a conduit that will not scour.

permit man

A member of a geophysical field party whose duty is to obtain permission from landowners for the party to work on their lands, or from public officials for the party to work along highways.


See: permitted explosive; permitted light.

permitted explosive

a. Explosive that has passed the Buxton tests and has been placed on the British list of authorized explosives, implying that they are reasonably safe to manufacture, handle, transport, and use in safety-lamp mines. Upon detonation, a permitted explosive: (1) gives off the minimum possible quantity of noxious gases, and (2) produces a flame of the lowest possible temperature and shortest possible duration, to lessen the risk of combustible gases ignition. The explosive contains cooling agents, such as sodium chloride and sodium bicarbonate. The first British list of permitted explosives was published in 1899.

b. A permitted explosive is one that has been approved for use in coal mines where there is any possible risk of igniting combustible gases or coal dust. In Great Britain, an explosive is approved by the Minister of Power and placed on the Permitted List after it has passed the official gallery tests prescribed for the particular class of explosives to which it belongs. These tests are carried out at the Safety in Mines Research Establishment's Testing Station at Buxton. c. Permitted explosives are divided into four groups: P.1., normal permitted explosives; P.2., sheathed explosives; P.3., eq.s. explosive; P.4., permitted explosives that have passed additional and more stringent tests. d. The term "permissible explosive" is used in the United States. See also: permissible explosive.

permitted light

Locked safety lamp or any other means of lighting, the use of which below ground in British coal mines is authorized by Regulations under the Act. See also: safety-lamp mine.

permitting process

A process in which an applicant files forms to a regulatory agency with required narratives, maps, mine plans, etc., to ensure in advance of mining that the proposed operation will be in compliance with the applicable environmental standards.


Strata not differentiated between the Permian and Carboniferous systems, particularly in regions where there is no conspicuous stratigraphic break and fossils are transitional.


Strata not differentiated between the Permian and Triassic systems, particularly in regions where the boundary occurs within a nonmarine, red beds succession.

permutite process

See: base exchange. Also spelled permutit process.


See: perovskite.

Perosa process

A process by which beryllium is extracted from beryl.


a. An orthorhombic mineral, CaTiO (sub 3) ; may have Ca replaced by rare earths and Ti replaced by niobium and tantalum; pseudocubic; massive or in cubic crystals; yellow, brown, or grayish black; occurs in silica-deficient metamorphic and igneous environments such as skarns; also occurs in mafic and alkaline igneous rocks. Also spelled perofskite.

b. The mineral group latrappite, loparite, leushite, and perovskite.


a. A header extending through a wall so that one end appears on each side of it; a perpendstone border, bondstone, throughstone; through binder. Also called parping; perpender; perpent.

b. A vertical joint, such as in a brick wall.

perpendicular separation

The separation of a fault as measured at right angles to the fault plane.

perpendicular slip

The component of the slip of a fault that is measured perpendicular to the trace of the fault on any intersecting surface.

perpendicular throw

The distance between the two parts of a disrupted bed, dike, vein, or of any recognizable surface, measured perpendicular to the bedding plane or surface in question. It is measured in a vertical plane at right angles to the strike of the disrupted surface. See also: throw.


A term proposed by Clarke (1908) to replace acidic. Syn: silicic. CF: subsilicic; mediosilicic.


Continuous; orebodies are often persistent in depth and metal contents.

personnel proximity survey

A survey of radiation conditions at positions occupied by personnel working near apparatus emitting radioactivity.


Deep sorption of gas by liquid.


A common term for crowbar, lever, or some such article used as a manual aid in moving heavy objects.


A variety of alkali feldspar consisting of parallel or subparallel intergrowths in which the potassium-rich phase (commonly microcline) appears to be the host from which the sodium-rich phase (commonly albite) exsolved; such exsolved areas may be visible to the naked eye, typically forming strings, lamellae, blebs, films, or irregular veinlets; where texture is invisible to the eye but can be resolved with a microscope, it is microperthite. CF: antiperthite; cryptoperthite; microperthite.


A deep-seated igneous rock consisting of alkali feldspar with less than 3% dark minerals. Feldspar, both orthoclase and albite, may be perthitically intergrown as cryptoperthite or as anorthoclase.


See: permeable.


A monoclinic mineral, LiAlSi (sub 4) O (sub 10) ; perfect cleavage; vitreous; resembles spodumene; a source of lithium salts; in granite pegmatites.


Resembling a flower petal in form, appearance, or texture. Applied to the structure seen in minerals that split into pieces with a smooth polished concave-convex surface that fit into one another somewhat like the petals of an unopened flower bud.


A small drain valve.


To fail gradually in size, quantity, or quality; e.g., the mine has petered out. Also called peter out.

petering out

The gradual thinning of a vein until it disappears.

Petersen grab

In the Petersen (or van Veen) type of grab, two semicircular buckets of varying sizes are hinged along a central axis. The buckets are held apart for lowering from a ship to the bottom by some form of catch. On striking the bottom, this is released so that on hoisting, the buckets move around on their axis, take a bite out of the sediment, and come together to form a closed container. With this configuration, the rate at which the grab hits the bottom affects the bite, and when the ship is drifting, a poor sample may be obtained if the grab does not hit the bottom vertically. See also: grab sampler.


Abbrev. for pentaerythritol tetranitrate. See also: penthrite.


An explosive compounded of ammonium carbonate, nitrated wood or charcoal, and saltpeter.


A process of fossilization whereby organic matter is converted into a stony substance by the infiltration of water containing dissolved inorganic matter (e.g., calcium carbonate, silica), which replaces the original organic materials, sometimes retaining the structure. Syn: petrification.


See: petrifaction.

petrified moss

See: tufa.

petrified rose

An aggregate or cluster of tabular crystals of barite, forming chiefly in sandstone, enclosing sandy grains within the crystals; sand cemented by barite with the crystal form of the latter. Syn: barite rosette. See also: rosette.

petrified wood

See: silicified wood.


Combining form meaning stone or rock.


Any of several materials and compounds present in, or derived from, natural gas or crude petroleum by physical refining or by chemical reaction.


a. The study of the chemical composition of rocks.

b. The study of the chemistry of petroleum and its products.


The study of spatial relations, esp. on a microscale, of the structural-textural units that comprise a rock, including a study of the movements that produced these elements. The units may be rock fragments, mineral grains, or cleavages.


A branch of petrology that deals with the origin of rocks. Syn: lithogenesis; petrogeny. CF: genesis.

petrogenic element

An element that is characteristically concentrated in ordinary rock types as opposed to ore deposits. CF: metallogenic element.


See: petrogenesis.


Person who is versed in or engaged in petrography, or the study of rocks.


Pertaining to the study of rocks.

petrographic microscope

A microscope specially fitted with optical, esp. polarizers, and mechanical accessories for identifying and studying the properties of minerals in granular form or in thin section.

petrographic province

A natural region within which some or all of the igneous rocks present certain well-marked peculiarities in their mineralogical and chemical composition, structure, texture, etc., that set them apart from rocks of other petrographic provinces. Consanguineous, comagmatic. Syn: comagmatic region.


A general term for the science dealing with the description and systematical classification of rocks, based on observations in the field, on hand specimens, and on thin sections. Petrography is thus wider in its scope than lithology, but more restricted than petrology, which implies interpretation as well as description.

petroleum coke

Cokelike material found in cavities of igneous rocks intrusive into carbonaceous sediments.

petroleum ether

A mixture of hydrocarbons boiling from 40 to 60 degrees C; a mixture of low-boiling liquid alkanes.

petroleum-oil cannel coal

See: oil shale.


A general term for the study, by all available methods, of the natural history of rocks, including their origins, present conditions, alterations, and decay. Petrology comprises petrography on the one hand, and petrogenesis on the other, and properly considered, its subject matter includes ore deposits and mineral deposits in general, as well as rocks in the more limited sense in which that term is generally understood.


See: oil shale.


Study of the physical properties of rock.


See: structural petrology.


Said of a material that resembles stone in its hardness; e.g., petrous phosphates. Little used.


See: china stone.


An isometric mineral, Ag (sub 3) AuTe (sub 2) ; metallic; steel gray to iron black; massive; sp gr, 8.7 to 9.02; in gold-bearing telluride veins; may be a significant source of gold and silver.