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

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See: emildine.

emanation deposit

An ore deposit of gaseous magmatic origin.


A linear structure, usually of earth or gravel, constructed so as to extend above the natural ground surface and designed to hold back water from overflowing a level tract of land, to retain water in a reservoir, tailings in a pond, or a stream in its channel, or to carry a roadway or railroad; e.g., a dike, seawall, or fill.


a. Penetration of microcrystalline groundmass material into phenocrysts, making their normal euhedral boundaries incomplete. An irregular corrosion or modification of the outline of a crystal by the magma from which it previously crystallized or in which it occurs as a foreign inclusion; esp. the deep corrosion into the sides of a phenocryst. The penetration of a crystal by another, generally euhedral, crystal. Such a crystal is called an embayed crystal.

b. A downwarped area containing stratified rocks, either sedimentary or volcanic or both, that extends into a terrain of other rocks, e.g., the Mississippi Embayment of the U.S. Gulf Coast.


a. Sectile, ductile; occurs as gray, yellowish or greenish-gray hornlike masses, waxy coatings, or crusts, as a secondary mineral in the oxidized zone of silver deposits; commonly associated with native silver, manganese oxides, and secondary lead and copper minerals.

b. The chief source of silver in some Chilean mines occurring as yellow-green incrustations and masses. It occurs in Australia at Broken Hill, New South Wales, and at Silver Reef, Victoria; widespread in the silver mining districts of the United States. Syn: horn silver.


Reduction in the normal ductility of a metal because of a physical or chemical change.


a. A brilliant green gem variety of beryl, highly prized as a gemstone. The color, which is caused by chromium or vanadium impurity, ranges from medium-light to medium-dark tones of slightly bluish green to slightly yellowish green. Syn: smaragd.

b. Any of various gemstones having a green color; e.g., oriental emerald (sapphire), copper emerald (dioptase), Brazilian emerald (tourmaline), or Uralian emerald (demantoid variety of andradite garnet). c. Said of a gemmy and richly green-colored mineral; e.g., emerald jade (jadeite), emerald spodumene (variety hiddenite), or emerald malachite (dioptase).

emerald copper

See: dioptase.

emerald cut

A step cut in which the finished gem is square or rectangular and the rows (steps) of elongated facets on the crown and pavilion are parallel to the girdle with sets on each of the four sides and in some cases at the corners; commonly used on diamonds to emphasize the absence of color and on emeralds and other colored stones to enhance the color. CF: step cut.

emerald filter

See: emerald glass.

emerald glass

The trade name for a color filter through which genuine emeralds and some other genuine stones appear reddish to violetish while glass imitations and some genuine stones appear greenish. Syn: beryloscope. See also: Walton filter.


A misnomer for chalcedony stained green with chromic oxide. It is a deeper green than nickel-stained chalcedony and, unlike the nickel types, shows a red residual color under the dichromatic filter.

emerald jade

Semitransparent to translucent jadeite of emerald color. Syn: imperial jade.

emerald loupe

See: Walton filter.

emerald malachite

See: dioptase.

emerald nickel

See: zaratite.

emerald triplet

An assembled stone commonly consisting of a crown and pavilion of rock crystal bound together by transparent green cement or a thin piece of green sintered glass; immersed in water and viewed sideways, the top and bottom are colorless with a line of color along the girdle. Green or colorless beryl may be used for the crown and possibly for the pavilion. Glass may be used for the pavilion, and sometimes for the crown as well, but the trade still calls it an emerald triplet. Syn: Soude emerald. See also: tripletine. CF: triplet.


A misnomer for dioptase.


a. A change in the levels of water and land such that the land is relatively higher and areas formerly under water are exposed; it results either from an uplift of the land or from a fall of the water level. Ant: submergence.

b. The point where an underground stream appears at the surface to become a surface stream. Syn: resurgence; rise; rising.


An impure mineral of the corundum or aluminum oxide type used extensively as an abrasive before the development of electric-furnace products. See also: emery rock.

emery rock

A granular rock that is composed essentially of an impure mixture of corundum, magnetite, and spinel, and that may be formed by magmatic segregation or by metamorphism of highly aluminous sediments. Syn: emery; corundolite.


A variety of spessartine garnet, with yttrium substituting for manganese up to 2%, in pegmatites at Elk Mountain, NM. See: spessartine.


See: emildine.

emission spectra

Monochromatic light from quantized electron transitions in thermally excited ions or atoms. CF: absorption spectra.

emission spectrum

A spectrum regarded as characterizing the body that emits the rays rather than one through which they pass.

emission standards

The maximum amount of pollutant permitted to be discharged from a single polluting source.


The ratio of radiant energy emitted by a body to that emitted by a perfect black body. A perfect black body has an emissivity of 1; a perfect reflector an emissivity of 0.


A triclinic mineral, Fe (sub 2) (TeO (sub 3) ) (sub 3) .2H (sub 2) O ; in yellow-green microcrystalline masses, fibrous crusts, patches of minute acicular crystals, or thin scaly coatings in the oxidation zones of gold and silver telluride districts of North and Central America.

Emory picker

A chute with narrow opening for the cleaning of coal. The slate, traveling slowly because of friction, falls into the openings and thus is removed from the coal, which, rolling freely down the incline, is carried over the narrow gap.

Empire drill

a. A light, hand-operated churn drill for testing placers from 10 to 125 ft (3.0 to 38.1 m) deep, though it is more commonly used for shallower holes. It consists of a string of 4-in (10.2-cm) casing, to the lower end of which is screwed a toothed cutting shoe. To the upper part, projecting above the ground, is fastened a round steel platform on which workers stand while operating the drilling tools. The casing can be turned by workers or a horse on the end of a long sweep fastened to the platform. The core of material inside the casing is loosened and brought to the surface by a drill pump on the end of a string of rods. CF: Banka drill.

b. A term often misused as a synonym for churn drill.


A process by which igneous rock intrudes, or an orebody is formed in older rocks.


An orthorhombic mineral, CuBiS (sub 2) ; metallic, grayish to tin-white, acicular to prismatic crystals with longitudinal striations; sp gr, 6.3 to 6.5; associated with chalcopyrite and other sulfides in silver veins or bismuth-rich parts of contact metamorphic deposits; may be confused with bismuthinite.


See: emplectite.


An orthorhombic mineral, AgTe ; forms fine granular, pale-bronze masses; sp gr, 7.61; associated with galena and native tellurium at the Empress Josephine Mine, Kerber Creek district, CO.


An empty car, truck, tub, box, or wagon.

empty-car puller

In bituminous coal mining, a laborer who pulls empty cars from cage or detaches them from hoisting cable when hoisting of loaded cars is done on one side of the shaft or haulage slope and lowering is done on the other.

empty rope

Any winding or hauling rope from which the load upon it has been removed.

empty track

A track for storing empty mine cars.

empty trip

Applies to empty coal, ore, and waste cars returning for another load.

Ems method

The condensation of dust and fumes from calcining furnaces by use of large flues filled with parallel rows of sheet iron.


The phenomenon of holding finely divided particles of a liquid in suspension within the body of another liquid. Banka method.


a. See: mud mixer.

b. A saponifying or other agent added to water and oil or water and resins, causing them to form an emulsion.


a. A liquid mixture in which a fatty or resinous substance is suspended in minute particles almost equivalent to molecular dispersion.

b. A suspension of one finely divided liquid phase in another.

emulsion texture

An ore texture showing minute blebs or rounded inclusions of one mineral irregularly distributed in another.


Having crystal forms that, while possessing neither a plane nor a center of symmetry, may occur in two positions that are mirror images of one another. The two positions cannot be converted into each other by any rotation, but are related to each other as are the right and left hand, hence designated right- and left-handed forms. Enantiomorphous crystals cause circular polarization of light, e.g., quartz.


In crystallography, similar in form but not superposable related to each other as the right hand is to the left, hence, one the mirror image of the other.


An orthorhombic mineral, Cu (sub 3) AsS (sub 4) ; dimorphous with luzonite, metallic gray-black; in vein and replacement copper deposits as small crystals or granular masses; an important ore of copper and arsenic; may contain up to 7% antimony; localities include Butte, MT; Chuquicamata, Chile; Cerro de Pasco, Colquijirca, Peru; Tsumeb, Namibia; and Bor, Serbia.

en cabochon

Cut in a style characterized by a smooth-domed, but unfaceted, surface; e.g., a ruby cut en cabochon in order to bring out the star. Etymol: French. See also: cabochon. Commonly used for garnets (carbuncles) and for those gems that depend for their beauty largely upon minute oriented inclusions (e.g., crocidolite, star ruby, or sapphire), the plan of the stone being circular or oval.


a. To work coal or mineral beyond the boundary that divides one mine area from another; to work coal from a barrier pillar that has been left as a safety measure. Also called trespass.

b. The advancement of water, replacing withdrawn oil or gas in a reservoir.


a. A crust or coating of minerals formed on a rock surface; e.g., calcite on cave objects, soluble salts on a playa, or manganese-rich crusts on the ocean or lake floor.

b. The process by which a crust or coating is formed. Syn: incrustation.


a. The secondary cleavage more or less at right angles to the bord or face cleat.

b. A direction parallel to the main natural line of cleat or cleavage in coal. Also called end line. c. Solid rock face at the termination of a tunnel.

end-bump table

A mechanically operated, sloping table by which heavy and light materials are separated. The end motion imparted to the table tends to drive all minerals up the slope of the table, but a flow of water carries the light materials down faster than the mechanical motion carries them up. The heavy materials settle to the bottom and finally reach the upper end and are delivered into a proper receptacle. The Gilpin County, Imlay, and Golden Gate concentrators are the chief types. Syn: Imlay table.

end cleat

See: butt cleat.

end clinometer

A clinometer designed to be fitted only to the bottom end of a drillrod string, as contrasted with a line clinometer that can be coupled into the drillrod string at any point between two rods.

end-discharge tippler

A framework to discharge the coal or mineral from a mine car or a wagon by elevating the rear end and to deliver the load from its front end onto a screen, chute, or bunker below track level.

end-dump car

See: mine car.

end dumping

Process in which earth is pushed over the edge of a deep fill and allowed to roll down the slope.


See: bournonite.


See: bournonite.


A monoclinic mineral, Al (sub 2) Si (sub 2) O (sub 5) (OH) (sub 4) .2H (sub 2) O ; kaolinite-serpentine group; soft, colorless to white; commonly tinted by impurities. (It is called halloysite in European literature.) Formerly called hydrated halloysite, hydrohalloysite, hydrokaolin.

end face

A coal face that is at right angles to the main cleats in the seam.

end-fired furnace

A furnace with fuel supplied from the end wall.


a. Gate at the front end of a car as it travels toward the dump. This gate has hooks that are engaged at the dump by stirrups that lift it, so that when the dump pitches forward the coal slides under the uplifted endgate and is discharged onto a chute or over a dump pile.

b. A gate leading to and at right angles to an end face. Also called ending.

endgate car

A mine car constructed with one hinged end that lifts up as the car is tilted down, permitting the coal, ore, and waste to run out. See also: mine car.


a. A road driven at right angles to the end cleat.

b. Eng. An adit driven in a direction with the grain of the coal.


A pillar method of working. See also: narrow work.

endless chain

A device for hauling coal in which a chain passes from the engine along one side of the road, around a pulley at the far end, and back again on the other side of the road. Empty cars, attached to one side of the chain by various kinds of clips or hooks, are hauled into the mine; loaded cars attached to the other side of the chain are hauled out of the mine.

endless rope

A rope that moves in one direction, one part of which carries loaded cars from a mine at the same time that another part brings the empties into the mine.


An arsenatian variety of vanadinite, intermediate in composition between vanadinite and mimetite.


The boundary lines of a mining claim that cross the general course of the vein at the surface. If the side lines cross the course of the vein instead of running parallel with it, they then constitute endlines. When a mining claim crosses the course of the lode or vein instead of being along such lode or vein, the endlines are those that measure the width of the claim as it crosses the lode.

endlines not parallel

Extralateral rights are allowed on a claim whose endlines converge, but they are not allowed in case the endlines diverge. Converging endlines on a claim would have the disadvantage of giving the owner of such a claim a continually diminishing length of vein on working down the dip.

end member

a. One of the two or more simple compounds of which an isomorphous (solid-solution) series is composed. For example, the end members of the plagioclase feldspar series are albite, NaAlSi (sub 3) O (sub 8) , and anorthite, CaAl (sub 2) Si (sub 2) O (sub 8) . Syn: minal.

b. One of the two extremes of a series; e.g., types of sedimentary rock or of fossils.


See: endogenetic.


Derived from within; said of a geologic process, or of its resultant feature or rock, that originates within the Earth, e.g., volcanism, volcanoes, extrusive rocks. The term is also applied to chemical precipitates, e.g., evaporites, and to ore deposits that originate within the rocks that contain them. CF: exogenetic; hypogene. Syn: endogene; endogenic; endogenous.

endogenetic effects

See: endomorphism.


See: endogenetic.


See: endogenetic.


See: endomorphism.


A crystal surrounded by another crystal of a different mineral species. Adj. endomorphic, endomorphous.


Pertaining to contact metamorphism that takes place within the cooling intrusive rock; resulting from the reaction of the wall rock upon the peripheral portion of an intrusion.

endomorphic metamorphism

See: endomorphism.


Changes within an igneous rock produced by the complete or partial assimilation of country-rock fragments or by reaction upon it by the country rock along the contact surfaces. It is a form of contact metamorphism with emphasis on changes produced within the igneous body rather than in the country rock. The term was originated by Fournet in 1867. CF: exomorphism. Partial syn: endogenetic effects. Syn: endometamorphism; endomorphic metamorphism.


Working a seam of coal, etc., at right angles to the cleat, or natural planes of cleavage.

end-on working

Working of coal seam at right angles to the natural cleats, joints, or slips.


In gemology, an instrument that affords a magnified image of the drill hole of a pearl, used to distinguish between genuine and cultured pearl. A tiny beam of light is directed into the walls of the drill hole to reveal whether the structure of the pearl's core is concentric (genuine) or parallel (cultured).

endostratic formation

Bedding in clays resulting from alternating, desiccation, and saturation by groundwater.


Accompanied by the absorption of heat. Opposite of exothermic.


In timbering, where both a cap and a sill are used, and posts act as dividers, the posts become the endplates. See: sideplate.

end-port furnace

A furnace with ports for fuel and air in the end wall.


York. Headings driven on the end or end-on.

end slicing

See: top slicing combined with ore caving.

end span

A span that is a slab or a continuous beam at its interior support.


The ability of a metal or a fabricated structure to recover from or to withstand repeated stress loadings or fluctuations.

endurance limit

That stress below which a material can withstand hundreds of millions of repetitions of stress without fracturing. It is considerably lower than rupture strength. Syn: fatigue limit.


a. The brick, concrete, or stonework construction at the sides of an excavation built to carry a flat or arched roof. Also called sidewall.

b. The vertical refractory wall, farthest from the furnace chamber, of the downtake of an open-hearth steel furnace. c. One of the two vertical walls terminating a battery of coke ovens or a bench of gas retorts; it is generally constructed of refractory bricks and heat-insulating bricks with an exterior facing of building bricks.

en echelon

Said of geologic features that are in an overlapping or staggered arrangement, e.g., faults. Each is relatively short, but collectively they form a linear zone, in which the strike of the individual features is oblique to that of the zone as a whole. Etymol: French en echelon, in steplike arrangement.


Minute, colorless, monoclinic, lath-shaped crystals, presumably a hydrocarbon; found in chemawinite (variety of amber), Cedar Lake, MB, Canada.

energizing coil

Primary coil that is used in inductive methods to set up electric currents in the Earth.


a. The ability of a body to perform work.

b. The capacity for producing motion. Energy holds matter together. It can become mass, or it can be derived from mass. It takes such forms as kinetic, potential, heat, chemical, electrical, and atomic energy, and it can be changed from one of these forms to another. c. Kinetic energy is that due to motion, and potential energy is that due to position. In a stream, for example, the total energy at any section is represented by the sum of its potential and kinetic energies.

engineering geology

Geology as applied to engineering practice, esp. mining and civil engineering. As defined by the Association of Engineering Geologists (1969), it is the application of geologic data, techniques, and principles to the study of naturally occurring rock and soil materials or ground water for the purpose of ensuring that geologic factors affecting the location, planning, design, construction, operation, and maintenance of engineering structures, and the development of ground-water resources, are properly recognized and adequately interpreted, utilized, and presented for use in engineering practice. Syn: geologic engineering.

engineering system

Any member of any assemblage of members such as a composite column, a coupling, a truss, or other structure.

engine pit

Eng.; Scot. A shaft used entirely for pumping purposes.

engine plane

a. A system of rope haulage in which the loads are raised or lowered on the slope by a steam or electric hoist. In the simplest form only one track and one rope are required, and power is used for raising the load. Double engine planes have two separate tracks or three rails and a passing turnout.

b. A roadway, horizontal or inclined, on which tubs or cars are hauled by rope haulage. c. Direct rope haulage.

engine tenter

N. Staff. See: brakeman.

English cupellation

A method of refining silver in which a small reverberatory furnace with a movable bed and a fixed roof is used. The bullion is charged gradually, and the silver is refined in the same furnace where the cupellation is carried on.


An orthorhombic mineral, K (sub 3) Na (sub 2) Ca (sub 10) Al (sub 15) (PO (sub 4) ) (sub 21) (OH) (sub 7) .26H (sub 2) O ; occurs with crandallite, wardite, and other phosphate minerals in variscite nodules at Fairfield, UT, and in the Tip Top pegmatite, SD.

English method

A method of smelting lead ore in which the characteristics are a large charge of lead ore, a quick roasting, a high temperature throughout, and the aim to extract all the lead in the reverberatory. The hearth inclines toward the middle of one of the sides, the lead collects in the furnace and is tapped at intervals into an outside kettle.

English process

In copper smelting, the process of reduction in a reverberatory furnace, after roasting, if necessary.

English zinc furnace

A furnace in which zinc is reduced and distilled from calcined ores in crucibles.


The clogging of a furnace.


a. A mineral or rock having cavities containing water.

b. See: enhydros.


A hollow nodule or geode of chalcedony containing water, possibly in large amounts. Syn: enhydrite.


Containing water; having drops of included fluid; as enhydrous chalcedony.


See: aenigmatite.

enlarging shots

Boreholes driven after the face of the rock has been unkeyed, and two or three free faces have thus been provided.

en masse conveyor

A conveyor comprising a series of skeleton or solid flights on an endless chain or other linkage that operates in horizontal, inclined, or vertical paths within a closely fitted casing for the carrying run. The bulk material is conveyed and elevated en masse in a substantially continuous stream with a full cross section of the casing. Also called chain conveyor. Syn: continuous stream conveyor.

en masse feeder

See: conveyor-type feeder.

enriched uranium

See: uranium.


See: supergene enrichment.

Ensign-Bickford hot-wire lighter

A fuse lighter similar to a Fourth-of-July sparkler, that burns for 2-1/2 min, sufficient time to light 30 to 50 fuses. The lead splitter is a lead tube of diameter about 1/8 in (3.2 mm) in filled with a slow-burning powder that burns at the rate of 36 s/ft (118 s/m) with a hot splitting flame.

Ensign-Bickford master fuse lighter

A shell, similar to a shotgun cartridge, that contains an ignition compound in the base. As many as seven fuses can be pushed into the shell until the fuses contact the ignition compound. The lighting of one fuse, which burns into the shell, sets off the compound and ignites the other six fuses.


An orthorhombic mineral, 2[MgSiO (sub 3) ] ; pyroxene group; dimorphous with clinoenstatite; a common rock-forming mineral in basalt, gabbro, norite, pyroxenite, and peridotite. Formerly called amblystegite, bronzite, chladnite, ficinite, hypersthene (in part), orthobronzite, orthoenstatite, orthohypersthene (in part), paulite, peckhamite, protobasite, shepardite, and victorite. See also: pyroxene. Symbol, En.


A group name for the orthopyroxenes of the MgSiO (sub 3) -FeSiO (sub 3) isomorphous series. It includes enstatite, hypersthene, and orthoferrosilite. CF: clinoenstenite.


The process of picking up and carrying along, as the collecting and movement of sediment by currents, or the incorporation of air bubbles into a cement slurry.


a. A measure of the unavailable energy in a system; i.e., energy that cannot be converted into another form of energy.

b. A measure of the mixing of different kinds of sediment; high entropy is approach to unmixed sediment of one kind. c. Ratio of amount of heat added to air to the absolute temperature at which it is added. Measured in Btu. d. Specific entropy is the ratio of entropy to weight of substance.


a. In coal mining a haulage road, gangway, or airway to the surface.

b. An underground passage used for haulage or ventilation, or as a manway. Back entry, the air course parallel to and below an entry. Distinguished from straight entry, front entry, or main entry. Dip entry, an entry driven downhill so that water will stand at the face directly down a steep dip slope. Gob entry, a wide entry with a heap of refuse or gob along one side. Slab entry, an entry that is widened or slabbed to provide a working place for a second miner. Double entry, a system of opening a mine by two parallel entries; the air current is brought into the rooms through one entry and out through the parallel entry or air course. Cutoff entry, an entry driven to intersect another and furnish a more convenient outlet for the coal. Single entry, a system of opening a mine by driving a single entry only, in place of a pair of entries. The air current returns along the face of the rooms, which must be kept open. Triple entry, a system of opening a mine by driving three parallel entries for the main entries. Twin entry, a pair of entries close together and carrying the air current in and out, so laid out that rooms can be worked from both entries. Also called double entry. c. A coal heading. To develop a coal mine in the United States, one or more sets of main entries are driven into the take. Each set consists of four to eight coal headings, connected at intervals by crosscuts. From these, and usually at right angles, butt entries, three to six in number, are driven at intervals of up to 1,500 yd (1.37 km). Between the sets of butt entries, face entries, three to four in number, are driven at intervals of up to 500 yd (0.46 km) to form a block or panel. The entries to split the panels may be 12 to 20 ft (3.7 to 6.1 m) wide and at 50- to 100-ft (15.2- to 30.5-m) centers. Each entry is made as productive as possible, and productivity is often higher in the entry work than in pillar extraction. See also: pillar-and-stall.

entry air course

A passage for air parallel to an entry.

entry conveyor

See: underground mine conveyor; entry table.

entry driver

A combination mining machine designed and built to work in entries and other narrow places, and to load coal as it is broken down. An undercutting frame and two vertical shearing frames serve to undercut and shear the sides of the coal, so that the ram equipped with bars and operated by hydraulic jacks can break down the coal. The height at which the ram operates against the coal, when the undercut and shearing are completed, is adjustable. A conveyor in the undercutting frame carries the broken-down coal back to another conveyor mounted on a turntable so that the coal can be loaded into a mine car, or slate can be deposited on the gob side of the entry. The entire machine is mounted in a pan.

entry driver operator

In bituminous coal mining, one who operates a type of coal cutter known as a heading machine that is adapted to the driving of underground haulageways in coal from one part of the mine to another or to the surface. Also called entry driving machine operator.


a. A miner who works in an entry.

b. One who enters upon public land with intent to secure an allotment under homestead, mining, or other laws. c. In anthracite and bituminous coal mining, one who is engaged in driving a haulageway, airway, or passageway from one place to another in the mine or to the surface. Also called heading driver.

entry stumps

Pillars of coal left in the mouths of abandoned rooms to support the road, entry, or gangway until the entry pillars are drawn. In Arkansas, these pillars are called entry stumps even when the rooms are first driven, before any pillars are pulled or the rooms abandoned.

entry table


a. The outer or covering part of a fold, esp. of a folded structure that includes some sort of structural break. CF: core.

b. A metamorphic rock surrounding an igneous intrusion. c. In a mineral, an outer part different in origin from an inner part.

environmental assessment

An analysis of environmental conditions which may involve baseline environmental analyses and data gathered with regard to zoological, botanical, geologic, and economic factors. This data may be utilized for environmental impact statements. Abbrev.: EA.

environmental audit

An evaluation of environmental conditions at a particular facility or site. Major items that could be relevant to an environmental audit for a mining facility may include information on permits, surface and mineral rights, mine ownership and violations, archaeological sites, hydrology issues, air pollution, waste disposal, impoundments, mine fires, underground injections and previously mined areas.

Environmental Impact Statement

A statement which is prepared by a Federal agency with regard to a permit, and is required under the National Environmental Policy Act (NEPA). The EIS may include but is not limited to information relating to the purposes and needs to which the agency is responding by the preparation of the EIS, alternatives, and the environmental consequences which may arise from the proposed action.


a. Pertaining to the wind; esp. said of such deposits as loess and dune sand, of sedimentary structures such as wind-formed ripple marks, or of erosion and deposition accomplished by the wind.

b. Said of the active phase of a dune cycle, marked by diminished vegetal control and increased dune growth. Etymol: Aeolus, god of the winds. Syn: aeolian.

eolian deposit

Wind-deposited accumulations, such as loess and dune sand.


A consolidated sedimentary rock consisting of clastic material deposited by the wind; e.g., dune sand cemented below ground-water level by calcite.

eolian placer

A placer concentrated by wind action.


a. The formal geochronologic unit of highest rank, next above era. The Phanerozoic Eon encompasses the Paleozoic, Mesozoic, and Cenozoic Eras.

b. One billion years. Also spelled aeon.


A monoclinic mineral, MnAl(PO (sub 4) )(OH) (sub 2) .H (sub 2) O ; forms a series with childrenite; pink to rose red; in granite pegmatites associated with manganese phosphates.

Eoetvoes balance

A sensitive torsion balance for measuring variations in the density of the underlying rocks; it records the horizontal gradient of gravity.

Eoetvoes torsion

See: torsion balance.

Eoetvoes torsion balance

See: torsion balance.


A five-sided step-cut gem resembling a shoulder ornament (epaulet) in outline.


See: epeirogeny.


As defined by Gilbert (1890), a form of diastrophism that has produced the larger features of the continents and oceans, for example, plateaus and basins, in contrast to the more localized process of orogeny, which has produced mountain chains. Epeirogenic movements are primarily vertical, either upward or downward, and have affected large parts of the continents, not only in the cratons but also in stabilized former orogenic belts, where they have produced most of the present mountainous topography. Some epeirogenic and orogenic structures grade into each other in detail, but most of them contrast strongly. Adj. epeirogenic. Syn: epeirogenesis.


A prefix signifying on or upon. CF: cata-.


Asterism seen by reflected light, as in star ruby or sapphire cut en cabochon to reveal asteria. The effect is created when light is reflected from suitably oriented inclusions within the stone.

epibenthic dredge

A bottom sampler consisting of a pair of sheet-metal skis attached to a light framework for a silk or nylon net. Removable rakers in front of the net stir up the bottom as the dredge advances, permitting the net to capture the benthic fauna and flora contained in the sediment. A bottom-walking wheel connected to a small counter indicates the distance over the bottom the device travels during a haul.


In oceanography, animals and plants found living below low tidemark and above the 100-fathom (183-m) line.


Situated upon a continental plateau or platform, as an epicontinental sea.


A name proposed as a replacement for epidiorite.


An orthorhombic mineral, NaBeSi (sub 3) O (sub 7) (OH) ; dimorphous with eudidymite; forms colorless tabular crystals in nepheline-syenite pegmatites with albite, elpidite, and analcime at Mont St. Hilare, PQ, Canada; Narsarsuk, Greenland; and Langesundfjord, Norway.


A metamorphosed gabbro or diabase in which generally fibrous amphibole (uralite) has replaced the original clinopyroxene (commonly augite). It is usually massive but may have some schistosity. See also: epidiabase.


A metamorphic rock consisting of epidote and quartz, and generally containing other secondary minerals such as uralite and chlorite.


a. A basic silicate of aluminum, calcium, and iron. One form is CA (sub 2) (Fe (super 3+) ,Al) (sub 3) (SiO (sub 4) ) (sub 3) (OH) ; monoclinic; Mohs hardness, 6 to 7; sp gr, 3.25 to 3.5; and a common secondary constituent of igneous rocks.

b. A monoclinic mineral, 2[Ca (sub 2) FeAl (sub 2) O(OH)(Si (sub 2) O (sub 7) )(SiO (sub 4) )] ; green; forms a series with clinozoisite; a common rock-forming mineral with albite and chlorite in low-grade metamorphic rocks and an accessory in some igneous rocks; may be used as a minor gemstone; formerly called pistacite, arendalite, delphinite, thalalite. c. The mineral group allanite, allanite-(Y), clinozoisite, epidote, hancockite, mukhinite, piemontite, and zoisite.


The hydrothermal introduction of epidote into rocks or the alteration of rocks in which plagioclase is albitized, freeing the anorthite molecule for the formation of epidote and zoisite, often accompanied by chloritization. These processes are characteristically associated with metamorphism.


a. Said of a geologic process, or of its resultant features, occurring at or near the Earth's surface. CF: hypogene. Syn: epigenic.

b. Pertaining to a crystal that is not natural to its enclosing material; e.g., a pseudomorph.


a. The change in the mineral character of a rock as a result of external influences operating near the Earth's surface, e.g., mineral replacement during metamorphism.

b. The changes, transformations, or processes, occurring at low temperatures and pressures, that affect sedimentary rocks subsequent to their compaction, exclusive of surficial alteration (weathering) and metamorphism; e.g., postdepositional dolomitization.


a. Said of a mineral deposit formed later than the enclosing rocks. CF: syngenetic.

b. Produced on or near the Earth's surface, e.g., epigenetic valleys, etc. c. In ore petrology, applied to mineral deposits of later origin than the enclosing rocks or to the formation of secondary minerals by alteration. Syn: epigenic.


See: epigene; epigenetic.


An orthorhombic(?) mineral, (Cu,Fe) (sub 5) AsS (sub 6) (?) ; metallic gray; forms prismatic crystals resembling arsenopyrite implanted on barite at the Neugl#1.uck Mine near Wittichen, Germany.


See: schoepite.


See: deuteric.

epineritic environment

The marine bottoms to a maximum depth of 20 fathoms (36.6 m).


An apophysis or tongue of an intrusion which is detached from its source. Also spelled epiphesis. See also: tongue.


In oceanography, plankton found in depths of less than 100 fathoms (183 m).


A monoclinic mineral, Ca[Al (sub 2) Si (sub 6) O (sub 16) ].5H (sub 2) O ; zeolite group; dimorphous with goosecreekite; forms radiating spherical aggregates of prismatic crystals in cavities in basalt and andesite, or with beryl in pegmatites.


A triclinic mineral, Na (sub 2) (Nb,Ti) (sub 2) Si (sub 2) O (sub 9) .nH (sub 2) O ; forms soft, pearly white rectangular plates in curved folia in the Julianehaab district of Greenland and the Lovozero alkali massif, Kola Peninsula, Russia.


a. Induced orientation of the crystal lattice of an electrodeposit at the plane of contact with the undisturbed underlying metal.

b. Orientation of one crystal with that of the crystalline substrate on which it grew; e.g., halite growing on a cleavage plane of mica because the mesh of the net of halite nearly coincides in shape and size with the pseudohexagonal net of the mica substrate. Adj: epitactic, epitaxic, epitaxial. CF: distaxy; topotaxy; syntaxy.


Said of a hydrothermal mineral deposit formed within about 1 km of the Earth's surface and in the temperature range of 50 to 200 degrees C, occurring mainly as veins. Also, said of that depositional environment. CF: hypothermal deposit; mesothermal; leptothermal; telethermal; xenothermal.


According to Grubenmann's classification of metamorphic rocks (1904), the uppermost depth zone of metamorphism, characterized by low to moderate temperatures (less than 300 degrees C) and hydrostatic pressures with low to high shearing stress. Modern usage stresses pressure-temperature conditions (low metamorphic grade) rather than the likely depth of zone. CF: mesozone; katazone.


a. The formal geochronologic unit, longer than an age and shorter than a period, during which the rocks of the corresponding series were formed.

b. A term used informally to designate a length (usually short) of geologic time; e.g., glacial epoch.


An orthorhombic mineral, MgSO (sub 4) .7H (sub 2) O ; bitter tasting; forms efflorescences of prismatic crystals, botryoidal masses, or incrustations on cave and mine walls from oxidizing sulfide minerals; also lacustrine deposits, mineral springs, and fumaroles. Syn: epsom salt; bitter salt; hair salt. See also: kieserite.

epsom salt

See: epsomite.

eq.s. explosive

An unsheathed explosive incorporating cooling agents, which is equivalent in safety (relating to the ignition of methane-air mixture) on a charge-weight basis to an explosive having a sheath of cooling agents around it. Abbrev. for equivalent-to-sheathed explosive.

equal-errors cut point

The density at which equal portions of the feed material are wrongly placed in each of two products of a specific-gravity separation. Syn: wolf cut point.

equal-errors size

The separation size at which equal portions of the feed material are wrongly placed in each of two products of a sizing operation.

equal-falling particles

Particles possessing equal terminal velocities. They are the oversize material and form the underflow of a classifier. See also: Stokes' law; terminal velocity.

equalization of winding load

The balancing of the weight of the winding rope, which varies considerably during a winding cycle. See also: balance rope; winding; winding drum.

equal lay

Ropes of which the layers of wires in strands have all been laid to the same length of lay. Also known as parallel lay. See also: Warrington.


a. Said of a crystal having the same or nearly the same diameter in all directions. CF: anisodesmic; tabular; prismatic. Syn: equidimensional; isometric.

b. Said of a sedimentary particle whose length is less than 1.5 times its width. c. Said of a rock in which the majority of grains are equant. d. Refers to crystals with roughly equal dimensions. CF: tabular; lathlike; rodlike; acicular.

equant element

A fabric element all of whose dimensions are approx. equal. CF: linear element; planar element.

equation of motion

The Newtonian law of motion states that the product of mass and acceleration equals the vector sum of the forces.

equiaxed crystals

Polyhedral crystals formed by spontaneous crystallization in the interior of a mass of metal in a mold. Distinguished from columnar crystals and chill crystals.


See: equant.


Said of crystals that have the same (or nearly the same) shape.


A textural term applied to rocks, the essential minerals of which are all of the same order of size.


a. A perfect balance of physical forces such that when two or more forces act upon a body, the body remains at rest.

b. The state in which a reversible chemical reaction is proceeding at the same rate in each direction. Metastable equilibrium is a steady unsatisfied state that will undergo further change on addition of the phase necessary to complete its stability. Physical equilibrium can connote stable coexistence of a substance in two or more phases, such as solid, liquid, and/or vapor. c. In geology, a balance between form and process, e.g., between the resistance of rocks along a coast and the erosional force of the waves. d. That state of a chemical system in which the phases do not undergo any change of properties with the passage of time, provided they have the same properties when the same conditions are again reached by a different procedure.

equilibrium diagram

See: phase diagram. CF: constitution diagram.

equilibrium eutectic

The composition within any system of two or more crystalline phases that melts completely at the lowest temperature; the temperature at which such a composition melts.

equilibrium moisture content

The moisture content of a soil when the water is static.

equilibrium moisture of coal

The moisture content retained at equilibrium in an atmosphere over a saturated solution of potassium sulfate at 30 degrees C, and 96% to 97% relative humidity. When the sample, before such equilibrium, contains total moisture at or above the equilibrium moisture, the equilibrium moisture may be considered as equivalent to inherent or bed moisture, and any excess may be considered as extraneous moisture.

equipment flowsheet

A diagram indicating, preferably by symbols, the units of plant to be used in the various operational steps carried out within a coal-preparation plant.

equipotential line

a. A line along which water will rise to the same elevation in piezometric tubes.

b. A line along which the potential is everywhere constant for the attractive forces concerned.

equipotential-line method

A technique used in electrical prospecting requiring artificial currents. It is based on the principle that if two electrodes are inserted in the ground and an external voltage is applied across them, there will be a flow of current through the earth from one electrode to the other. If the medium through which the current flows is homogeneous in its electrical properties, the flow lines will be regular and in a horizontal plane, symmetrical about the line joining the electrodes. Any inhomogeneities in these properties will cause distortions in the lines of current flow. Such distortions indicate the existence of buried material with either higher conductivity than its surroundings, so that it attracts the flow lines toward itself, or with lower conductivity, so that it tends to force the lines into the surrounding medium.

equipotential surface

A surface on which the potential is everywhere constant for the attractive forces concerned. The gravity vector is everywhere normal to a gravity equipotential surface; the geoid is an equipotential. Syn: gravity equipotential surface; niveau surface; level surface.


Corresponding in geologic age or stratigraphic position; esp. said of strata or formations (in regions far from each other) that are contemporaneous in time of formation or deposition or that contain the same fossil forms. n. A stratum that is contemporaneous or equivalent in time or character.

equivalent circuit

An electrical network, the frequency response of which is identical to that of a quartz oscillator plate.

equivalent diameter

a. The diameter of a hypothetical sphere composed of material having the same specific gravity as that of the actual particle and of such size that it will settle in a given liquid at the same terminal velocity as the actual particle. Also called equivalent size.

b. Twice the equivalent radius.

equivalent evaporation

The quantity of water that would be evaporated by a given apparatus if the water is received by the apparatus at 212 degrees F (100 degrees C), and vaporized at that temperature under atmospheric pressure. It is expressed in kilograms per hour.

equivalent freefalling diameter

See: equivalent particle diameter.

equivalent grade

In textural classification, refers to the arithmetic mean size.

equivalent length

The resistance of a mine airway obstruction, duct or pipe elbow, valve, damper, orifice, bend, fitting, or other obstruction to flow, expressed in the number of feet of straight airway, duct, or pipe of the same cross section that would have the same resistance.

equivalent orifice

A term that compares the resistance of air of a mine to the resistance of a circular opening in a thin plate through which the same quantity of air flows under the same pressure as in the mine.

equivalent particle diameter

A concept used in evaluating the size of fine particles by a sedimentation process; it is defined as the diameter of a sphere that has the same density and the same freefalling velocity in any given fluid as the particle in question. CF: particle size. Syn: equivalent freefalling diameter.

equivalent radius

a. The radius of a spherical particle of density 2.65 (the density of quartz) which would have the same rate of settling as the given particle.

b. A measure of particle size, equal to the computed radius of a hypothetical sphere of specific gravity 2.65 (quartz) having the same settling velocity and same density as those calculated for a given sedimentary particle in the same fluid; one half of the equivalent diameter.

equivalent temperature

A composite of mean radiant temperature and air temperature; also defined as the mean temperature of the environment effective in controlling the rate of sensible heat loss from a black body in still air when the surface temperature and size of the black body are comparable to those of the human body. Where the enclosure surface (mean radiant temperature) and air temperatures are equal, this temperature is also the British equivalent temperature; when not equal, the British equivalent temperature is that temperature at which a body with an 80 degrees F (26.7 degrees C) surface temperature will lose sensible heat at the same rate as in the given environment. Syn: British equivalent temperature.

equivolumnar wave

See: distortional wave; S wave; transverse wave.


The formal geochronologic unit next in order of magnitude below an eon, during which the rocks of the corresponding erathem were formed; e.g., the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era. Each of these includes two or more periods, during each of which a system of rocks was formed. Long-recognized Precambrian Eras are the Archeozoic (older) and Proterozoic (younger).


Former spelling of jeremejevite, also spelled eremeevite.


An orthorhombic mineral, (Fe,Mg,Mn) (sub 3) B (sub 7) O (sub 13) Cl ; forms a series with boracite; dimorphous with congolite; Mohs hardness of 7 to 7-1/2; forms pseudocubes in halite-anhydrite deposits in the Harz Mountains, Germany.


A U.S. trademark name for a yellowish-green synthetic spinel.


A casein plastic used for molding many common objects and possibly for inferior gem imitations; sp gr, about 1.33; refractive index, 1.53 to 1.54.


An orthorhombic mineral, CuCl (sub 2) .2H (sub 2) O ; forms a sublimate of soft bluish-green woollike aggregates on the sides of fumaroles. Syn: antofagasite; erythrocalcite.


The group of physical and chemical processes by which earth or rock material is loosened or dissolved and removed from any part of the Earth's surface. It includes the processes of weathering, solution, corrosion, and transportation. The mechanical wear and transportation are effected by rain, running water, waves, moving ice, or winds, which use rock fragments to pound or to grind other rocks to powder or sand.

erosional unconformity

An unconformity that separates older rocks that have been subjected to erosion from younger sediments that cover them; specif. disconformity.

erosion channel

See: classical washout.

erosion surface

a. A land surface shaped and subdued by the action of erosion, esp. by running water. The term is generally applied to a level or nearly level surface.

b. An area that has been flattened by subaerial or marine erosion to form an area of relatively low relief at an elevation close to the base level (sea level) existing at the time of its formation. Relics of such surfaces may now be found far above sea level owing to the falling base level, below the present ocean surface.

erosion thrust

A thrust fault along which the hanging wall moved across an erosion surface.


A rock fragment carried by glacial ice or by floating ice, deposited at some distance from the outcrop from which it was derived, and generally though not necessarily resting on bedrock of different lithology. Size ranges from a pebble to a house-size block.

error curve

A partition curve drawn to defined conventional scales with the portion showing recoveries over 50% reversed to enclose an error area. Syn: tromp error curve.

error of closure

a. Of a traverse, the amount by which the computed position of the last point of the traverse fails to coincide with the initial point; i.e., the length of line necessary to close the traverse. Frequently, also, the ratio of the linear error of closure to the perimeter (also known as the error of the survey).

b. Of angles, the amount by which the sum of the measured angles fails to equal the true sum. c. Of azimuths, the amount by which the measurement of the azimuth of the first line of a traverse, made after completing the circuit, fails to equal the initial measurement. d. Of a level circuit, the amount by which the last computed elevation fails to equal the initial elevation; or the amount by which the differences of elevation in a circuit fail to add up (algebraically) to zero. e. Of a horizon, the amount by which the sum of the angles measured around the horizon differs from 360 degrees . f. Of a triangle, the amount by which the sum of the three angles of a triangle differs from the true sum; i.e., 180 degrees plus the spherical excess.


See: bornite.


Said of a rock formed by the solidification of magma; i.e., either an extrusive or an intrusive rock. Most writers restrict the term to its extrusive or volcanic sense.


See: erythrite.


A monoclinic mineral, 2[Co (sub 3) (AsO (sub 4) ) (sub 2) .8H (sub 2) O] ; forms a series with annbergite and with hoernesite; occurs in soft pink to crimson crystals, globular or reniform masses, or earthy encrustations as a weathering product of cobalt ores in the oxidized parts of nickel-arsenic-silver-bearing veins; used as ore indicator for cobalt and possibly silver. Syn: erythrine. See also: cobalt bloom; red cobalt; cobalt ocher; peachblossom ore.


See: eriochalcite.


a. Eng. A second or additional shaft by which miners may get out of the mine in case of accident to the other shafts. Also an upcast; escape pit; escapeway.

b. A wasteway for discharging the entire flow of a stream.

escape shaft

A shaft driven esp. to permit egress from the mine in case of emergency.


exit is obstructed.


a. A long, more or less continuous cliff or relatively steep slope facing in one general direction, breaking the continuity of the land by separating two level or gently sloping surfaces, and produced by erosion or by faulting. The term is often used synonymously with scarp, although escarpment is more often applied to a cliff formed by differential erosion.

b. A steep, abrupt face of rock, often presented by the highest strata in a line of cliffs, and generally marking the outcrop of a resistant layer occurring in a series of gently dipping softer strata; specif. the steep face of a cuesta. CF: cuesta.

Eschka's mixture

A mixture of two parts magnesium and one part dried sodium carbonate; used as a reagent for determining sulfur in coal or coke.


See: aeschynite.


A tetragonal mineral, CuFeSe (sub 2) ; chalcopyrite group; forms a series with chalcopyrite; is metallic brass yellow; variably magnetic; with chalcopyrite, clausthalite, and naumannite in dolomite veins, Eskeborn adit, Tilkerode, Harz Mountains, Germany.


A trigonal mineral, Cr (sub 2) O (sub 3) ; hematite group; easily confused with hematite and magnetite; in a chromium-bearing tremolite skarn at the Outokumpu Mine, Finland.

Esperanza classifier

A classifier of the free-settling type in which the settled material is removed by dragging it up an inclined plane by means of a continuous belt of flat blades or paddles. It is continuous in its operation.


A broad bench or terrace bordering a canyon, esp. in the plateau areas of the southwestern United States.

espley rock

A conglomerate or breccia with rapid lateral passage through grit to fine sandstone; cement usually ferruginous with some lime and alumina. Characteristically developed amid variegated clays of Etruria Marl group of Upper Coal Measures in the English Midlands.

essential mineral

A mineral component of a rock that is necessary to the classification and nomenclature of the rock, but that is not necessarily present in large amounts. CF: accessory mineral. Syn: specific mineral.


An alkali gabbro primarily composed of plagioclase, hornblende, biotite, and titanaugite, with lesser amounts of alkali feldspar and nepheline. Essexite grades into theralite with a decrease in potassium feldspar and an increase in the feldspathoid minerals. Its name is derived from Essex County, MA.


A yellow-brown or reddish-brown transparent gem variety of grossular garnet containing iron. Syn: cinnamon stone; hyacinth; jacinth. See: hessonite.


A massive variety of apatite found in Estramadura, Spain. A phosphate ore.

estuarine deposit

A sedimentary deposit laid down in the brackish water of an estuary, characterized by fine-grained sediments (chiefly clay and silt) of marine and fluvial origin mixed with a high proportion of decomposed terrestrial organic matter; it is finer grained and of more uniform composition than a deltaic deposit.


a. The seaward end or the funnel-shaped tidal mouth of a river valley where fresh water comes into contact with seawater and where tidal effects are evident.

b. A portion of an ocean or an arm of the sea affected by fresh water; e.g., the Baltic Sea. c. A drowned river mouth formed by the subsidence of land near the coast or by the rise of sea level.

etch angle

The angle formed between the true horizon and the actual plane of the etch ring in an acid bottle as measured before capillarity corrections. Also called apparent angle. See also: capillarity. CF: apparent dip.

etch figure

A marking, commonly in the form of minute pits, produced by a solvent on a crystal surface; the form varies with the mineral species and the solvent, but reflects the symmetry of the structure; also called etching figure.


A process of engraving in which lines, frosting, or roughening are produced by an acid or mordant. Often used in studying the composition and structure of metals, sandgrains, and crystals.

etch line

A line of demarcation between the etched and unetched portions of the inside of an acid bottle, used to determine the inclination of a borehole by an acid-dip survey.

etch method

A method, using a soda-lime glass tube partially filled with a dilute solution of hydrofluoric acid, of determining the angle at which a borehole is inclined at any specific point of its course below the collar. See also: acid-dip survey.

etch pattern

Regular surface marking developed by solvent action on smooth surface of alloy or crystal, and characteristic for that specific substance. The reagent used is an etchant, usually of an acid in water or alcohol.

etch ring

See: etch line.

etch time

The time required for a dilute solution of hydrofluoric acid of a specific strength to etch the inside of an acid bottle enough so that the line of demarcation between the etched and unetched portions of the acid bottle is clearly discernible. Also known as etching time.

etch tube

See: acid-etch tube.


See: acetamide.


See: alcohol.

ethical gemology

The study of the correct and incorrect nomenclature of gems, with emphasis on clarifying names and terms that may mislead or deceive purchasers.


See acetylene.


A crosscutting intrusive body of plutonic rock that narrows downward.


Used as an electrolyte to transform coal into a tan-gray substance with a relatively high hydrogen-to-carbon ratio.

ethylene glycol

A highly explosive liquid HOCH (sub 2) CH (sub 2) OH ; somewhat volatile; nonfreezing; explosive base. Used as an antifreeze.


See: acetylene.


a. Leucite nephelinite.

b. A dark-colored extrusive rock intermediate in composition between leucitite and nephelinite with phenocrysts of clinopyroxene in a dense groundmass of leucite, nepheline, and clinopyroxene. The name is not included in the IUGS classification of extrusive igneous rocks.


A collective name for fluid, viscid, and solid bitumens that are easily soluble in organic solvents. Petroleum, ozokerite, elaterite, and asphalt are examples.


An orthorhombic mineral, CuAgSe ; soft; sp gr, 7.6 to 7.8; in most deposits of selenium minerals, associated with unangite, klockmannite, and clausthalite, e.g., Smaland, Sweden; Copiapo, Chile; and the Harz Mountains, Germany. Also spelled eukairite.

eucalyptus oil

Frothing agent used in flotation. Essential oil distilled from leaves of eucalyptus trees.


An orthorhombic mineral, (K,Na) (sub 8) Cu (sub 9) (SO (sub 4) ) (sub 10) (OH) (sub 6) (?) ; emerald green; forms thin incrustations on lava and fumarole deposits on Mt. Vesuvius, Italy.


An orthorhombic mineral, Cu (sub 2) (AsO (sub 4) )(OH).3H (sub 2) O ; vitreous; transparent to translucent; emerald or leek green; associated with azurite, malachite, or olivenite in the oxidation zones of copper deposits.


A monoclinic mineral, 4[BeAlSiO (sub 4) (OH)] ; vitreous; Mohs hardness, 7-1/2; in auriferous sands in Austria, Russia, Brazil, Peru, and Tasmania Australia; and used as a minor gemstone.


A variety of eudialyte that is optically negative and rich in calcium. Also spelled eukolite.


A trigonal mineral, LiAlSiO (sub 4) ; transparent, vitreous; fluoresces pink in UV light; Mohs hardness = 6-1/2; forms with albite in pegmatites. If heated, beta-eucryptite expands normal to the c axis, but contracts parallel to c.


See: macrocrystalline.


A trigonal mineral, Na (sub 4) (Ca,Ce) (sub 2) (Fe,Mn,Y)ZrSi (sub 8) O (sub 22) (OH,Cl) (sub 2) (?) ; weakly radioactive; in nepheline syenite and granite, commonly associated with arfvedsonite, sodalite, feldspar, aegirine, catapleiite, and astrophyllite. CF: eucolite. Syn: barsanovite.


A monoclinic mineral, NaBeSi (sub 3) O (sub 7) (OH) ; dimorphous with epididymite; vitreous, in transparent to translucent tabular crystals with lamellar twinning having one perfect and one imperfect cleavage; in nepheline-syenite pegmatites with albite, elpidite, and analcime.


An instrument for the volumetric measurement and analysis of gases.


a. Said of a mineral grain that is completely bounded by its own rational faces, and whose growth during crystallization or recrystallization was not restrained or interfered with by adjacent grains.

b. Said of the shape of such a crystal. Syn: idiomorphic. CF: anhedral; subhedral. See: automorphic.

Eulerian methods of current measurement

A measurement of the rate of flow past a geographically fixed point; current meter methods.


See: ferrosilite.


An isometric mineral, Bi (sub 4) (SiO (sub 4) ) (sub 3) ; vitreous, transparent to translucent tetrahedral crystals associated with native bismuth near Schneeberg, Saxony, Germany. Syn: bismuth blende.


A brownish-yellow resin with low oxygen content and a characteristic pleasant odor found in brown coal.


See: europium oxide.

europium oxide

Rare-earth oxide; pale rose; Eu (sub 2) O (sub 3) ; melting point, above 1,300 degrees C; and sp gr, 7.42. Used as a nuclear-control-rod material and in fluorescent glass. Syn: europia.


A well-matured organic ooze.


A grain-size comparator.


The worldwide sea-level regime and its fluctuations, caused by absolute changes in the quantity of seawater, e.g., by continental icecap fluctuations.


Pertaining to worldwide changes of sea level that affect all the oceans. Eustatic changes may have various causes, but the changes dominant in the last few million years were caused by additions of water to, or removal of water from, the continental icecaps.


Said of a stratified mineral deposit. CF: ataxic.


Said of the banded structure of certain extrusive rocks, which results in a streaked or blotched appearance. Also, said of a rock exhibiting such structure, e.g., a eutaxite. The bands or lenses were originally ejected as individual portions of magmas, were drawn out in a viscous state, and formed a heterogeneous mass in response to welding.


Said of a system consisting of two or more solid phases and a liquid whose composition can be expressed in terms of positive quantities of the solid phases, all coexisting at an (isobarically) invariant point, which is the minimum melting temperature for the assemblage of solids. Addition or removal of heat causes an increase or decrease, respectively, of the proportion of liquid to solid phases, but does not change the temperature of the system or the composition of any phases. See also: eutectoid.

eutectic point

The lowest temperature at which a eutectic mixture will melt. Syn: eutectic temperature.

eutectic ratio

The ratio of solid phases crystallizing from the eutectic liquid at the eutectic temperature. It is such as to yield a gross composition for the crystal mixture that is identical with that of the liquid. It is most frequently stated in terms of weight percent.

eutectic temperature

See: eutectic point.

eutectic texture

A pattern of intergrowth of two or more minerals, formed as they coprecipitate during crystallization, e.g., the quartz and feldspar of graphic granite. See also: exsolution texture. Syn: eutectoid texture.


The equivalent of eutectic, when applied to a system all of whose participating phases are crystalline.

eutectoid texture

See: eutectic texture.


In mineralogy, having distinct cleavage; cleaving readily.


Said of a body of water characterized by a high level of plant nutrients, with correspondingly high primary productivity.

eutrophic peat

Peat rich in plant nutrients, nitrogen, potassium, phosphorus, and calcium. Synonymous with calcareous peat.


Radioactive radium mineral found in Brazil.


An orthorhombic mineral, (Y,Ca,Ce,U,La,Th)(Nb,Ta,Ti) (sub 2) O (sub 6) ; forms a series with polycrase; brilliant to vitreous brown to black; in pegmatites and placers commonly with monazite in Canada; Madagascar; Norway; and Pennsylvania. A source of uranium, niobium, and tantalum. Formerly called loranskite.


a. Pertaining to an environment of restricted circulation and stagnant or anaerobic conditions, such as a fjord or a nearly isolated or silled basin with toxic bottom waters. Also, pertaining to the material (such as black organic sediments and hydrogen-sulfide muds) deposited in such an environment or basin, and to the process of deposition of such material (as in the Black Sea).

b. Pertaining to a rock facies that includes black shales and graphitic sediments of various kinds. Etymol: Greek euxenos, hospitable.