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

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A prefix meaning dark-colored.


An earthy variety of tenorite. See also: black copper ore; tenorite.


An early name for albertite.


A bituminous substance found in masses in the brown coal of Zweifelsruth, Bohemia, former Czechoslovakia. That part of this substance that is soluble in alcohol is termed rochlederite, the residue melanellite. Also spelled melanchym.


That portion of melanchyme that is insoluble in alcohol; it is black and gelatinous.


a. Diamonds of mixed sizes.

b. An assortment of mixed sizes of diamonds weighing more than 1/4 carat; e.g., larger than those of a melee. c. A body of rock mappable at a scale of 1:24,000 or smaller, characterized by a lack of internal continuity of contacts or strata and by the inclusion of fragments and blocks of all sizes, both exotic and native, embedded in a fragmental matrix of finer-grained material. Neither matrix composition and fabric nor genesis is significant for the definition.


See: melanocratic.


A titanian variety of andradite. Syn: black andradite garnet; pyreneite.


Applied to dark-colored rocks, esp. igneous rocks, containing between 60% and 100% dark minerals; i.e., rocks, the color index of which is between 60 and 100. CF: hypermelanic; leucocratic; mesocratic.


A trigonal mineral, Mn (sub 2) SbFeO (sub 6) . Originally named melanostibian.


An orthorhombic mineral, Pb (sub 2) Fe (sub 2) Si (sub 2) O (sub 9) ; forms a series with kentrolite.


A triclinic mineral, CaV (sub 4) O (sub 10) .5H (sub 2) O ; a natural vanadium bronze with perfect prismatic cleavage; at Cerro de Pasco, Peru, and on the Colorado Plateau.


a. A monoclinic mineral, FeSO (sub 4) .7H (sub 2) O ; green; tastes slightly sweet, astringent, and metallic; from the decomposition of pyrite.

b. The mineral group bieberite, boothite, mallardite, melanterite, and zincmelanterite. Syn: copperas; green vitriol; iron vitriol.


The narrowest part of an isogyre in an interference figure representing the point of emergence of an optic axis. CF: interference figure.


a. A collective term for small round faceted diamonds, such as those mounted in jewelry. The term is sometimes applied to colored stones of the same size and shape as the diamonds.

b. A small diamond cut from a fragment of a larger size. c. In diamond classification, a term for small round-cut diamonds weighing more than 1/4 carat. CF: melange. Etymol, French.


a. A tetragonal mineral in the series akermanite, Ca (sub 2) MgSi (sub 2) O (sub 7) -gehlinite, Ca (sub 2) Al(AlSi)O (sub 7) .

b. The mineral group akermanite, gehlenite, hardystonite, and melilite. Jeffreyite, leucophanite, and meliphanite are structurally similar. Also spelled mellilite.


A generally olivine-free extrusive rock composed of melilite and clinopyroxene (or other mafic mineral) usually comprising more than 90% of the rock, with minor amounts of feldspathoids and sometimes plagioclase.


a. A high explosive similar to lyddite; said to be chiefly picric acid.

b. A species of soft, unctuous clay, common in Bavaria, and probably identical with bole.


A tetragonal mineral, (Ca,Na) (sub 2) Be(Si,Al) (sub 2) (O,OH,F) (sub 7) ; structurally similar to the melilites. Also spelled meliphane. Syn: gugiaite.


Small cut diamonds, usually about one-eighth carat. Generally refers to stones used in jewelry.


See: melilite.


A tetragonal mineral, Al (sub 2) [C (sub 6) (COO) (sub 6) ].16H (sub 2) O; resinous; honey yellow; forms nodules in brown coal. Also spelled melinite, mellilite. (Not melite.) Syn: honey stone.


A silicate of ferric iron, calcium, etc., approaching garnet in composition, but with optical properties similar to those of an orthorhombic pyroxene. Formed by the action of basic slag on silica brick in a steel furnace.

mellow amber

See: gedanite.


a. A trigonal mineral, NiTe (sub 2) ; forms a series with merenskyite; (super ) one perfect cleavage; metallic reddish white; soft; sp gr, 7.3.

b. The mineral group berndtite, kitkaite, melonite, merenskyite, and moncheite. Syn: tellurnickel. (Not melanite.)


A dark-colored plutonic rock that is part of the ijolite series and contains nepheline and 60% to 90% mafic minerals, esp. green pyroxene. The name is from Melteig farm, Fen complex, Norway.

melting hole

The opening in the floor to a furnace in a melting house.

melting house

The building in which crucible furnaces for steel making are located.

melting point

That temperature at which a single, pure solid changes phase to a liquid or to a liquid plus another solid phase, upon the addition of heat at a specific pressure. Unless otherwise specified, melting points are usually stated in terms of 1 kPa. The term can also be used for the isothermal melting of certain mixtures, such as eutectic mixtures. Erroneously used also to refer to the temperature at which some appreciable but unspecified amount of liquid develops in a complex solid mixture that possesses a melting range; e.g., the melting point of granite. Abbrev.: mp or MP.

melting pot

A crucible.

melting shop

Open-hearth plant.

melting zone

The hottest part of a furnace, where melting takes place.


A division of a formation, generally of distinct lithologic character and of only local extent.

membrane filter

See: molecular filter sampler.

membrane theory

An advanced theory of design for thin shells, based on the premise that a shell cannot resist bending because it deflects. The only stresses that exist, therefore, in any section are shear stress and direct compression or tension.


a. A variety of ilmenite found as sand at Menaccan, Cornwall, Eng.

b. A black, magnetic sand from Cornwall, England, from which the element, titanium, was first isolated. Also spelled menachanite; manaccanite; menachite.


Eng. To load, or reload, trams at the gate ends out of smaller trams used only in the working faces of thin seams.


An orthorhombic mineral, Pb (sub 3) Cl (sub 2) O (sub 2) ; white; in the Mendip Hills, United Kingdom.


A monoclinic mineral, NaAl(SO (sub 4) ) (sub 2) .11H (sub 2) O . See also: soda alum.


An orthorhombic mineral, Pb (sub 13) CuSb (sub 7) S (sub 24) ; forms slender prismatic blackish lead-gray crystals.


European stage: Middle Cambrian (above Solvan, below Maentwrogian).


A concretionary, opaque, dull, grayish variety of opal. Syn: liver opal.


a. The curved top surface of a liquid column. It is concave upwards when the containing walls are wetted by some liquid (such as water in a vertical glass tube) and convex upwards when wetted with other liquids (such as mercury in a vertical glass tube).

b. A concavoconvex lens; esp., one of true crescent-shaped cross section.

men on!

Scot. A brief expression to indicate that workers are on the cage to be raised, or lowered, in a shaft.

Menzies cone separator

Consists of a 60 degrees cone with a short cylindrical top section. It is provided with a stirring shaft, located in its vertical axis, carrying several sets of horizontal arms with rings of nozzles projecting through the sides of the cone for the admission, at several horizons, of the required water currents. At the base of the cone, a classifier column several feet long is fitted, through which refuse discharges continuously to an inclined refuse conveyor. Water is supplied by a centrifugal pump. See also: cone classifier.

mephitic air

a. Carbon dioxide.

b. Air exhausted of oxygen and containing chiefly nitrogen.

mephitic gas

See: mephitic air.


A noxious exhalation caused by the decomposition of organic remains; applied also to gases emanating from deep sources, such as mines, caves, and volcanic regions.


A metal merchant, as distinct from a producer's agent or broker, often acts as a principal, buying metal or concentrate from producers and others and selling it to others. The merchant will often hold metal on personal account while waiting for a buyer.

merchant iron

Iron in the common bar form, which is convenient for the market. Also called merchant bar.

mercurial horn ore

See: calomel.


a. A liquid mineral, (trigonal below -38.87 degrees C); metallic silver to tin white; sp gr, 13.6; occurs as minute droplets in cinnabar and in some hot-spring deposits; amalgamates with many metals.

b. Symbol: Hg. Rarely occurs free in nature. Chief ore is cinnabar, HgS . Used in laboratory work for making thermometers, barometers, diffusion pumps, mercury-vapor lamps, advertising signs, and pesticides. Mercury is a virulent poison and is readily absorbed through the respiratory tract, gastrointestinal tract, or unbroken skin.

mercury gatherer

A stirring apparatus that causes mercury, which has become floured or mixed with sulfur in amalgamating, to resume the fluid condition, through the agency of mechanical agitation and rubbing.

mercury ore

Native mercury; same as cinnabar (sulfide).

mercury switch

A glass tube employing mercury to establish electrical contact between circuits when the tube is tilted so that the mercury bridges the gap between contacts, and conversely.

mercury-vapor lamp

Consists essentially of a sealed glass tube provided with two electrodes and containing a gas. When an electrical potential difference is applied, a current passes and with a suitable gas, light will be emitted. In the case of mercury vapor, this light is of a bluish color and has proven effective in distinguishing dirt from coal. A special starting electrode close to one of the main electrodes initiates the discharge, and a choke coil in series with the lamp serves to limit the current passing, since the resistance tends to fall with increasing current.


A prefix signifying part or portion.


See: hypocrystalline.


Any crystal form with fewer faces than the holohedral equivalent for the crystal system. CF: hemihedral; holohedral. See also: tetartohedral.


Coalified remains of parts of plants.


Any crystal class with less symmetry than the distribution of points in its lattice.


Biotite with its optic axial plane parallel to its b crystallographic axis.

Merrill-Crowe process

Removal of gold from pregnant cyanide solution by deoxygenation, followed by precipitation on zinc dust, followed by filtration to recover the resultant auriferous gold slimes.

Merrill filter

A type of plate and frame pressure filter.


a. High-purity zinc dust used to precipitate gold and silver in the cyanide process.

b. See: whitlockite.

Merrit plate

See: bloomery.

mersey yellow coal

See: tasmanite.


A monoclinic mineral, Ca (sub 3) Mg(SiO (sub 4) ) (sub 2) ; colorless to pale green.


An isolated, nearly level landmass standing distinctly above the surrounding country, bounded by abrupt or steeply sloping erosion scarps, and capped by a layer of resistant, nearly horizontal rock (often lava). CF: plateau. Etymol: Spanish, table.

Mesabi non-Bessemer ore

See: natural ore.


See: butte.

Mesa Grande tourmaline

Fine-quality tourmaline from a pegmatite near Mesa Grande, San Diego County, CA.


a. In ventilation, a series of airways that form a closed loop.

b. The screen number of the finest screen of a specified standard screen scale. c. The number of apertures per unit area of a screen (sieve).

mesh aperture

The dimension or dimensions of the aperture in a screen deck, usually with a qualification as to the shape of aperture; e.g., round-hole, square-mesh, and long-slot.

mesh fraction

That part of a material passing a specified mesh screen and retained by some stated finer mesh.

mesh liberation size

The particle size at which substantially all of the valuable minerals are detached from the gangue minerals.

mesh number

The designation of size of an abrasive grain, derived from the openings per linear inch in the control sieving screen. Syn: grit number.

mesh of grind

Optimum particle size resulting from a specific grinding operation, stated in terms of percentage of material passing (or alternatively being retained on) a given size screen. The mesh of grind is the liberation mesh decided on as correct for commercial treatment of the material. Abbrev., m.o.g.

mesh structure

A structure resembling network or latticework that is found in certain alteration products of minerals. Also called net structure; lattice structure.

mesh texture

a. A texture resembling a network, caused by the alteration of certain minerals; e.g., the serpentinization of olivine. Syn: reticulate texture.

b. An interlacing network of microveinlets of fibrous serpentine enclosing cores of more weakly birefringent cryptocrystalline serpentine in which relict remnants of olivine may survive. Also called net structure; lattice structure.


A prefix meaning middle. CF: cata-; meta-.


Applied to igneous rocks that are intermediate between leucocratic and melanocratic rocks; they contain 30% to 60% dark minerals. CF: melanocratic; leucocratic.


Said of the texture of a rock intermediate between microcrystalline and macrocrystalline; also, said of a rock with such a texture.


Said of a mineral deposit or enrichment of mingled hypogene and supergene solutions; also, said of such solutions and environment. CF: hypogene; supergene.


Group name for brown coals.


A monoclinic mineral, Na (sub 2) Ca (sub 2) [Al (sub 2) Si (sub 3) O (sub 10) ] (sub 3) .8H (sub 2) O ; zeolite group; pseudo-orthorhombic; in cavities in basalt and andesite, geodes, and hydrothermal veins. Syn: cotton stone; winchellite.


Microcline intermediate in structural state between orthoclase and maximum microcline. Syn: intermediate microcline. CF: maximum microcline.


The last-formed interstitial material between the larger mineral grains in an igneous rock or in a microcrystalline groundmass. CF: groundmass.


Said of a hydrothermal mineral deposit formed at considerable depth and in the temperature range of 200 to 300 degrees C. Also, said of that environment. CF: hypothermal deposit; epithermal; leptothermal; telethermal; xenothermal.

mesothermal deposit

A mineral deposit formed at moderate temperature and pressure, in and along fissures or other openings in rocks, by deposition at intermediate depths, from hydrothermal fluids. Mesothermal deposits are believed to have formed mostly between 175 degrees C and 300 degrees C at depths of 4,000 to 12,000 ft (1,220 to 3,660 m). Many valuable metalliferous deposits of western North America are of this type.


An era of geologic time, from the end of the Paleozoic to the beginning of the Cenozoic, or from about 225 million years to about 65 million years ago.


According to Grubenmann's classification of metamorphic rocks (1904), the intermediate-depth zone of metamorphism, which is characterized by temperatures of 300 to 500 degrees C and moderate hydrostatic pressure and shearing stress. Modern usage stresses temperature-pressure conditions (medium to high metamorphic grade) rather than the likely depth of zone. CF: katazone; epizone.


A triclinic mineral, Ca (sub 2) (Fe,Mn)(PO (sub 4) ) (sub 2) .2H (sub 2) O; fairfieldite group. Syn: neomesselite; parbigite. (Not mesolite.)


Port. Mine boss.


a. In petrology, indicates a metamorphosed protolith.

b. In mineralogy, indicates a mineral species that is a dehydration product of another mineral species or is a polymorph.


A prefix that, when used with the name of a sedimentary or igneous rock, indicates that the rock has been metamorphosed, e.g., metabasalt. CF: cata-; meso-.


A monoclinic mineral, Al (sub 4) (SO (sub 4) ) (sub 6) .27H (sub 2) O . See also: alunogen.


The rank of coal, within the anthracite class of Classification D-388, such that, on the dry and mineral-matter-free basis, the volatile matter content of the coal is equal to or less than 2% (or the fixed carbon is equal to or greater than 98%), and the coal is nonagglomerating.


An argillite that has been metamorphosed.


Arkose that has been welded or recrystallized by metamorphism so that it resembles a granite or a granitized sediment. CF: recomposed granite.


a. A tetragonal mineral, Ca(UO (sub 2) ) (sub 2) (PO (sub 4) ) (sub 2) . 2-6H (sub 2) O ; yellow; an alteration product of uraninite and other uranium-bearing minerals.

b. The mineral group abernathyite, bassetite, chernikovite, meta-ankoleite, meta-autunite, metaheinrichite, metakahlerite, metakirchheimerite, metalodevite, metanovacekite, metatorbernite, meta-uranocircite, meta-uranospinite, metazeunerite, sodium uranospinite, and uramphite.


A collective term, first used by Finnish geologists, for metamorphosed mafic rock that has lost all traces of its original texture and mineralogy owing to complete recrystallization.


a. Metamorphosed, altered, or somewhat indurated bentonite; characterized by clay minerals (esp. illite) that no longer have the property of absorbing or adsorbing large quantities of water; nonswelling bentonite, or bentonite that swells no more than do ordinary clays. The term has been applied to certain Ordovician clays of the Appalachian region and upper Mississippi River Valley. See also: potassium bentonite.

b. A mineral of the montmorillonite group with SiO (sub 2) layers in the montmorillonite structure.


Hard black lustrous variety of hydrocarbon found in proximity of igneous intrusions.


A term proposed by Barth (1962) for the redistribution of granitizing materials within sediments by mobilization, transfer, and reprecipitation, as opposed to metasomatism involving addition of new materials.


a. An old term for altered glassy trachyte.

b. Iron meteorite with the composition of an octahedrite but lacking Widmaenstatten figures.


An isometric mineral, HBO (sub 2) ; in crystalline aggregates in rock salt in Kazakhstan(?).


See: brushite.

metachemical metamorphism

A term proposed by Dana to describe metamorphism that involves a chemical change in the affected rocks.


An isometric mineral, HgS ; forms black tetrahedra; sp gr, 7.7; a source of mercury. Also called metacinnabarite. Also spelled: metacinnibar


A mineral of the same composition as a cinnabar, but black in color, and crystallizing in isometric forms (tetrahedral). Used as a source of mercury.


Leith's term for a rock possessing secondary cleavage, or cleavage in its modern meaning (1905). CF: protoclase.


Any large crystal developed in a metamorphic rock by recrystallization, such as garnet or staurolite in mica schists.


See: porphyroblast.


A contraction of metamorphic diabase, suggested by Dana for certain rocks simulating diabase, but which were possibly produced by the metamorphism of sedimentary rocks. CF: metadiorite.


a. A contraction of metamorphic diorite that was proposed for certain metamorphic rocks that resemble diorite, but which may have been the result of the metamorphism of sedimentary rocks. CF: metadiabase.

b. Metamorphosed gabbro, diabase, or diorite.


A metamorphic dolomite, or dolomite marble.


Durain of a high-rank bituminous coal. See also: durain.


A hieroglyph formed during metamorphism.


Dehydrated halloysite. See also: halloysite.


A tetragonal mineral, Ba(UO (sub 2) ) (sub 2) (AsO (sub 4) ) (sub 2) .8H (sub 2) O ; meta-autunite group; yellow; a secondary mineral. Syn: arsenuranocircite; metasandbergite. CF: heinrichite.


A monoclinic mineral, CaV (sub 6) O (sub 16) .3H (sub 2) O ; dark-red to yellow-brown; forms tabular crystals impregnating sandstone in southwest Colorado and southeast Utah. CF: hewettite.


A mineral, Fe (sub 2) (SO (sub 4) ) (sub 2) (OH) (sub 2) .3H (sub 2) O . See also: hohmannite.


A hydrous calcium and magnesium borate, CaMgB (sub 6) O (sub 8) (OH) (sub 6) .XH (sub 2) 0 ; like hydroboracite but with more water. Syn: inderborite.


A tetragonal mineral, Fe(UO (sub 2) ) (sub 2) (AsO (sub 4) ) (sub 2) .8H (sub 2) O; meta-autunite group.


A possibly tetragonal mineral, Co(UO (sub 2) ) (sub 2) (AsO (sub 4) ) (sub 2) .8H (sub 2) O ; meta-autunite group.


In most cases, an opaque, lustrous, elemental substance that is a good conductor of heat and electricity. It is also malleable and ductile, possesses high melting and boiling points, and tends to form positive ions in chemical compounds.

metal bath

A bath, such as of mercury or tin, employed for chemical processes requiring high temperatures.

metal drift

A drift or heading driven in barren and hard rock.


A name for isometric leucite that is stable above 625 degrees C. CF: pseudoleucite.


A metamorphosed carbonate rock not suitable for use as polished dimension stone (Brooks, 1954). CF: metamarble; ortholimestone.


A metallurgist.

metalized slurry blasting

The breaking of rocks, etc., using slurried explosive medium containing a powdered metal, such as powdered aluminum.


a. A term used to describe metal particles, such as gold in ores.

b. (adj.) The adj. indicates that the noun it modifies possesses metallic properties. These properties often include a metallike luster, conduction of electricity, tensile strength, opacity, and malleability, although some metallic materials may possess only a few such characteristics. c. When used with "mineral" in the context of resources, e.g., metallic mineral, it has a different and special meaning; it refers to the product, not the mineralogy. Thus chalcopyrite, CuFeS (sub 2) , is metallic (in the sense above), and the copper and iron it contains are metallic minerals in the resource sense. A single mineral, such as chalcopyrite, may also be the source of a nonmetal, sulfur. Adding to the confusion, rutile (TiO (sub 2) ) is the source of both titanium, which is used as metallic titanium, and titanium oxide, which is used as a nonmetallic mineral pigment. Because many industrial minerals (in a resource sense) tend to be nonmetallic (in either the mineralogical or the resource sense), the terms "industrial minerals" and "nonmetallic minerals" are sometimes carelessly used interchangeably. CF: mineral; nonmetallic mineral; industrial minerals. Syn: metalliferous.

metallic element

Element that is generally distinguishable from nonmetallic elements by its luster, malleability, and electrical conductivity, and its usual ability to form positive ions.

metallic iron

Metal iron, as distinguished from iron ore.

metallic luster

The ordinary luster of metals. When feebly displayed, it is termed submetallic. Gold, iron pyrites, and galena have a metallic luster, e.g., while chromite and cuprite have a submetallic luster.

metallic minerals

Minerals with a high specific gravity and metallic luster, such as titanium, rutile, tungsten, uranium, tin, lead, iron, etc. In general, the metallic minerals are good conductors of heat and electricity. See also: nonmetallic minerals.

metallic ore

From a strictly scientific point of view, the terms metallic ore and ore deposits have no clear significance. These are purely conventional expressions, used to describe those metalliferous minerals or bodies of mineral having economic value, from which useful metals can be advantageously extracted. In one sense, rock salt is an ore of sodium, and limestone an ore of calcium, but to term beds of those substances ore deposits would be quite outside of current usage.


Metal-bearing; specif., pertaining to a mineral deposit from which a metal or metals can be extracted by metallurgical processes. See also: metallic.

metalliferous mud

Marine deposit of mud formed under anoxic conditions and containing anomalously high quantities of zinc, silver, and copper, and lesser amounts of lead and gold. The term has most often been applied to deposits of muds in the Red Sea which have been formed by submarine precipitation of metallic sulfides from hydrothermal vents. These vents occur along the axis of a spreading center which forms the Red Sea Basin.


To convert into metal.


A word used to embrace all ores or metalliferous material.


The process or processes by which metals are introduced into a rock, resulting in an economically valuable deposit; the mineralization of metals.

metallogenetic epoch

The time interval favorable for the genesis or deposition of certain useful metals or minerals. Syn: minerogenetic epoch.

metallogenetic province

See: minerogenetic province.

metallogenic element

An element normally forming sulfides, selenides, tellurides, arsenides, antimonides, and/or sulfosalts, or occurring uncombined as a native element; i.e., an element of primary ore deposits.

metallogenic province

a. An area characterized by a particular assemblage of mineral deposits, or by one or more characteristic types of mineralization. A metallogenic province may have had more than one episode of mineralization. Syn: metallographic province.

b. See: minerogenetic province.


The study of the genesis of mineral deposits, with emphasis on its relationship in space and time to regional petrographic and tectonic features of the Earth's crust. The term has been used for both metallic and nonmetallic mineral deposits. Adj: metallogenic. Syn: ore geology. CF: genesis.


An optical instrument designed for both visual observation and photomicrography of prepared surfaces of opaque materials, at magnifications ranging from about 25 to about 1,500 diameters. The instrument consists of a high-intensity illuminating source, a microscope, and a camera bellows. On some instruments, provisions are made for examination of specimen surfaces with polarized light, phase contrast, oblique illumination, dark-field illumination, and customary bright-field illumination.

metallographic province

See: metallogenic province.


a. The science dealing with the constitution and structure of metals and alloys as revealed by the unaided eye or by tools, such as low-power magnification, optical microscope, electron microscope, and diffraction or X-ray techniques. See also: reflected-light microscope.

b. The study of the constitution and structure of metals and alloys.


a. A nonmetal, such as carbon or nitrogen, that can combine with a metal to form an alloy.

b. An element--such as boron, silicon, arsenic, or tellurium--intermediate in properties between the typical metals and nonmetals.

metalloidal luster

a. Reflecting light, somewhat like a metal, but less than metallic luster.

b. Having the luster of a semimetal; e.g., native bismuth or arsenic.

metallometric surveying

Geochemical prospecting term used by Russian authors for soil surveys or for the chemical analysis of systematically collected samples of soil and weathered rock.


The geochemical determination of metals.

metallo-organic compound

A compound in which a metal combines with organic compounds to form metallo-organic complexes, such as porphyrins and salts of various organic acids. Some metallo-organic compounds are soluble in water, others are not.

metallurgical balance sheet

Material balance of a process.

metallurgical coke

A coke with very high compressive strength at elevated temperatures, used in metallurgical furnaces, not only as a fuel, but also to support the weight of the charge.

metallurgical engineer

One who applies engineering principles to the science and technology of metallurgy. CF: metallurgist.

metallurgical fume

A mixture of fine particles of elements and metallic and nonmetallic compounds either sublimed or condensed from the vapor state.

metallurgical smoke

A term applied to the gases and vapors, and fine dust entrained by them, that issue from the throats of furnaces; consists of three distinct substances: gases (including air), flue dust, and the fume.


One who is skilled in, or who practices, metallurgy. CF: metallurgical engineer.


a. The science and art of separating metals and metallic minerals from their ores by mechanical and chemical processes; the preparation of metalliferous materials from raw ore.

b. Study of the physical properties of metals as affected by composition, mechanical working, and heat treatment.

metal mining

The industry that supplies the community with the various metals and associated products. Similar to coal mining, it is an extractive industry, and once the raw material, the orebody, is depleted it is not replenishable. See also: vein miner.

metal notch

See: taphole.

metal pickling

The immersion of metal objects in an acid bath to remove scale, oxide, tarnish, etc., leaving a chemically clean surface for galvanizing or painting.

metal powder

a. Metallic elements or alloys in finely divided or powder form.

b. A general term applied by drillers, bit setters, and bit manufacturers to various finely ground metals, which, when mixed, are commonly used to produce sintered-metal diamond bit crowns. Also called powdered metal; powder metal.

metal stone

a. Newc. An argillaceous stone, shale, and sandstone.

b. Staff. See: ironstone.


A marble suitable for use as polished dimension stone; e.g., the Vermont metamarble. CF: orthomarble; metalimestone.


A metal ceramic consisting of high Cr.Al (sub 2) O (sub 3) .


a. A mineral that has become virtually amorphous owing to the breakdown of the original crystal structure by internal bombardment with alpha particles (helium nuclei) emitted by radioactive atoms within the mineral. Many green zircons, esp. those from Sri Lanka, which are Precambrian in age, and have thus had over 800 million years of this internal bombardment, owe their low refractive index and density to this cause, and may be termed metamict zircons.

b. Said of a mineral containing radioactive elements in which various degrees of lattice disruption and changes have taken place as a result of radiation damage, while its original external morphology has been retained. Examples occur in zircon, thorite and several other minerals. Not all minerals containing radioactive elements are metamict; e.g., xenotime and apatite are not.


The process of disruption of the structure of a crystal by radiations from contained radioactive atoms, rendering the material partly or wholly amorphous.

metamict mineral

A mineral whose crystal structure has been disrupted by radiation from contained radioactive particles.


a. The product of dehydration of montmorillonite at 400 degrees C.

b. A dehydrated smectite.


Pertaining to the process of metamorphism or to its results.

metamorphic aureole

See: aureole. CF: contact metamorphism.

metamorphic deposit

An ore deposit that has been subjected to great pressure, high temperature, and alteration by solutions. It may have become warped, twisted, or folded, and the original minerals may have been rearranged and recrystallized.

metamorphic differentiation

A collective term for the various processes by which minerals or mineral assemblages are locally segregated from an initially uniform parent rock during metamorphism; e.g., garnet porphyroblasts in fine-grained mica schist.

metamorphic diffusion

Migration, by diffusion, of materials from one part of a rock mass to another during metamorphism. Diffusion may involve chemically active fluids from magmatic sources, hot pore fluids, or fluids released from hydrous minerals or carbonates. Ionic diffusion in the solid state may also occur.

metamorphic facies

A set of metamorphic mineral assemblages, repeatedly associated in space and time, such that there is a constant and therefore predictable relation between mineral composition and chemical composition. It is generally assumed that the metamorphic facies represent the results of equilibrium crystallization of rocks under a restricted range of externally imposed physical conditions; e.g., temperature, lithostatic pressure, and water pressure. Syn: mineral facies.

metamorphic grade

The intensity or rank of metamorphism, measured by the amount or degree of difference between the original parent rock and the metamorphic rock. It indicates in a general way the pressure-temperature environment or facies in which the metamorphism took place. For example, conversion of shale to slate or phyllite would be low-grade dynamothermal metamorphism (greenschist facies), whereas its continued alteration to a garnet-sillimanite schist would be high-grade metamorphism (almandine-amphibolite facies). Syn: metamorphic rank. See also: high-rank metamorphism.

metamorphic overprint

See: overprint.

metamorphic rank

See: metamorphic grade.

metamorphic rock

Any rock derived from preexisting rocks by mineralogical, chemical, and/or structural changes, essentially in the solid state, in response to marked changes in temperature, pressure, shearing stress, and chemical environment, generally at depth in the Earth's crust.

metamorphic water

Water driven out of rocks by metamorphism.


The mineralogical, chemical, and structural adjustment of solid rocks to physical and chemical conditions that have generally been imposed at depth below the surface zones of weathering and cementation, and that differ from the conditions under which the rocks in question originated.


A triclinic mineral, CaV (sub 2) O (sub 6) .2H (sub 2) O ; pearly to dull yellow; a dehydration product of rossite. -< �?O rAO j+<�� � 2 DICTIONARY TERMS:metasandbergite See: metaheinrichite. See: metaheinrichite.


Compact sapropel rock.


A monoclinic mineral, Al (sub 2) (PO (sub 4) )(VO (sub 4) ).6H (sub 2) O .


Formerly called schoepite II. See also: schoepite; paraschoepite.


A sediment or sedimentary rock that shows evidence of having been subjected to metamorphism.


Shale altered by incipient metamorphic reconstitution but not recrystallized and without the development of partings or preferred mineral orientation.


See: metasomatism.


Pertaining to the process of metasomatism and to its results. The term is esp. used in connection with the origin of ore deposits.


The process of practically simultaneous capillary solution and deposition by which a new mineral of partly or wholly different chemical composition may grow in the body of an old mineral or mineral aggregate. The presence of interstitial, chemically active pore liquids or gases contained within a rock body or introduced from external sources is essential for the replacement process, that often, though not necessarily, occurs at constant volume with little disturbance of textural or structural features. Syn: metasomosis. CF: pyrometasomatism.


A rock produced by metasomatism.


a. A replacing mineral that grows in size at the expense of another mineral (the host or palasome); a mineral grain formed by metasomatism.

b. The newly formed part of a migmatite or composite rock, introduced during metasomatism.


See: metasomatism.


Monoclinic FePO (sub 4) .2H (sub 2) O , dimorphous with orthorhombic strengite; named to correspond with metavariscite and variscite AlPO (sub 4) .2H (sub 2) O . Syn: phosphosiderite; clinostrengite.


A tetragonal mineral, Cu(UO (sub 2) ) (sub 2) (PO (sub 4) ) (sub 2) .8H (sub 2) O ; meta-autunite group; strongly radioactive; emerald to apple green; occurs in granite pegmatites. CF: torbernite.


An orthorhombic mineral, Ca(UO (sub 2) ) (sub 2) V (sub 2) O (sub 8) .3H (sub 2) O ; yellow; radioactive; a secondary mineral.


A monoclinic mineral, Ba(UO (sub 2) ) (sub 2) (PO (sub 4) ) (sub 2) .8H (sub 2) O ; meta-autunite group; yellow green; radioactive; a secondary mineral in quartz veins.


A mineral, (UO (sub 2) ) (sub 6) (SO (sub 4) )(OH) (sub 10) .5H (sub 2) O; radioactive.


A tetragonal mineral, Ca(UO (sub 2) )(AsO (sub 4) ) (sub 2) .8H (sub 2) O; meta-autunite group.


A monoclinic mineral, AlPO (sub 4) .2H (sub 2) O ; green; dimorphous with variscite.


A monoclinic mineral, FeAl (sub 2) (PO (sub 4) ) (sub 2) (OH) (sub 2) .8H (sub 2) O ; dimorphous with paravauxite; forms acicular crystals or radiating fibrous aggregates.


The product of dehydration of vermiculite at 400 degrees C.


Said of partly metamorphosed volcanic rock.


A hexagonal mineral, K (sub 2) Na (sub 6) Fe (sub 7) (SO (sub 4) ) (sub 12) O (sub 2) .18H (sub 2) O .


a. A fibrous serpentine mineral; a variety of chrysotile.

b. See: micaceous sandstone.


A tetragonal mineral, Cu(UO (sub 2) ) (sub 2) (AsO (sub 4) ) (sub 2) .8H (sub 2) O ; meta-autunite group; grass to emerald green.

meteoric iron

a. Iron of meteoric origin.

b. An iron meteorite.

meteoric stone

a. A stone of meteoric origin; a stony meteorite.

b. A meteorite having the appearance of a stone.

meteoric water

Ground water of atmospheric origin.


A stony or metallic body that has fallen to the Earth's surface from outer space. Adj: meteoritic.


a. An instrument, apparatus, or machine for measuring fluids, gases, electric currents, etc., and recording the results obtained; e.g., a gasmeter, a watermeter, or an air meter.

b. The fundamental unit of length in the metric system equal to 39.37079 in or 3.2808 ft.

metering pin

A valve plunger that controls the rate of flow of a liquid or a gas.


CH (sub 4) ; carbureted hydrogen or marsh gas or combustible gases; formed by the decomposition of organic matter. The most common gas found in coal mines. It is a tasteless, colorless, nonpoisonous, and odorless gas; in mines the presence of impurities may give it a peculiar smell. It weighs less than air and may therefore form layers along the roof and occupy roof cavities. Methane will not support life or combustion; with air, however, it forms an explosive mixture, CH (sub 4) +2O (sub 2) -->CO (sub 2) .2H (sub 2) O. The gases resulting from a methane explosion are irrespirable. Methane is often referred to as combustible gases because it is the principal gas composing a mixture that, when combined with proper proportions of air, will explode when ignited. Breathing methane causes ill effects only where the air is so heavily laden with it that oxygen is supplanted. See also: colliery explosion; marsh gas; firedamp; limits of flammability.

methane drainage

a. Capture of the concentrated methane through boreholes drilled into a coalbed or associated strata.

b. Outside the United States three main systems of methane drainage have been developed: (1) the cross-measure borehole method, (2) the superjacent roadway system and (3) the pack cavity system. The cross-measure borehole method which consists of boring holes from 2-1/4 to 3-1/4 in (5.7 to 8.3 cm) in diameter and 150 to 300 ft (45 to 90 m) in length, into the strata above or below the seam, generally close to the working face. This method has the advantage of being suited to a wide variety of conditions and does not require another seam within reasonable distance above or below the seam to be drained, or the use of solid stowing Syn: cross-measure borehole system. In the superjacent roadway system, boreholes are drilled from a roadway situated above the seam being worked, the drainage of the methane then taking place from this roadway. In the pack cavity system, corridors are left and supported in the goaf as the face advances, and from these combustible gases is drawn off. Syn: combustible gases drainage; corridor system. c. In contrast to the above, methane drainage technology in the United States is conducted from the surface as well as underground. Underground methane drainage is primarily by means of horizontal boreholes drilled into the coalbed to be extracted. Surface methane drainage methods include vertical gob gas vent holes on longwall panels and hydraulically stimulated vertical wells generally drilled several years in advance of mining into virgin coalbeds.

methane monitoring system

A system whereby the methane content of the mine air is indicated automatically at all times. When the content reaches a predetermined concentration, the electric power is cut off automatically from each machine in the affected area. The mechanism is so devised that its setting cannot be altered. The system is used, mainly, in conjunction with the operation of continuous miners and power loaders.


An instrument for detecting methane in mine air. It contains an electric battery that sustains a small electric glow light. As soon as a certain percentage of methane enters the workings, a tiny explosion occurs in the fuse head, where a fine wire filament is melted and starts a bell ringing continuously.

methane recorder

An instrument that gives a continuous record of the methane concentration over a period of time.

methane removal

See: water infusion method.

methane tester

A methane detector. See also: methanometer.

methane tester type S.3

A nonautomatic methane detector approved under the regulations for use in coal mines. The instrument is normally calibrated at 1% methane, and this provides an accuracy of + or -0.05% over the most important part of the scale; i.e., 0.75% to 1.5%. It weighs 3-1/2 lb (1.6 kg), and the source of power is an Edison cap lamp battery.


An instrument for determining the methane content in mine air. See also: sampling instrument; catalytic methanometer.

methenyl tribromide

See: bromoform.

method of working

The system adopted to work or extract material in a mine. It includes all the operations involved in the cutting, handling, and transport of valuable material and waste rock, support of ground, ventilation of workings, and provision of supplies. The term does not include winding or hoisting, surface handling, and preparation or dressing. See also: coal mining methods.

method study

A study to provide the essential data on which mine management can operate in making the most effective use of workpower, machines, and materials. Method study has been applied in the mining industry for many years, although sometimes under different names. See also: time study; work study.

methyl acetone

A mixture of methyl acetate and acetone. Used as a solvent.

methylene iodide

A heavy liquid used for mineral separation (sp gr, 3.33); also for refractive index determination (R.I.=1.74). CF: Clerici solution; Sonstadt solution; Klein solution; bromoform.


Both capping and gossan.


A pocket implement combining the uses of many instruments, such as thermometer, level, plummet, and lens.

metric carat

An international unit equal to 200 mg that had been adopted in most European countries and in Japan when it was made the standard in the United States in 1913. Abbrev.: M.C. and cm. See also: carat.

Mexican diamond

Rock crystal (quartz).

Mexican onyx

Yellowish brown or greenish brown banded calcite. See also: onyx marble; Gibraltar stone.

Mexican turquoise

Turquoise from the central part of Baja California, Mexico.

Mexican water opal

A fire opal from Mexico.


A triclinic mineral, Ca (sub 2) B (sub 6) O (sub 6) (OH) (sub 10) .2H (sub 2) O ; forms prismatic, commonly tabular, crystals or is fibrous; an alteration product of inyoite from Inyo County, CA.


An amorphous mineral, WO (sub 3) .2H (sub 2) O ; resinous; yellow brown.