Appendix:Dictionary of Mining, Mineral, and Related Terms/C/8
crocidolite quartz
See: tiger's-eye.
crocoisite
See: crocoite.
crocoite
A monoclinic mineral, PbCrO (sub 4) ; bright-red, yellowish-red, or orange. Syn: red lead ore; crocoisite.
crocus
A term used in the Milford, NH, quarries to denote gneiss or any other rock in contact with granite.
crocus martis
A name used for impure red ferric oxide pigments and polishing powders, usually produced by heating iron sulfate containing calcium sulfate, lime, or other inert filler. Also sometimes applied more generally to other impure oxides of red or yellow color.
crocus of antimony
Brownish-yellow; mainly sodium or potassium thioantimonite; Na (sub 3) SbS (sub 3) or K (sub 3) SbS (sub 3) . Obtained as a slag in refining antimony.
cronstedtite
A monoclinic or trigonal mineral, Fe (super 2+) (sub 2) Fe (super 3+) (SiFe (super 3+) )O (sub 5) (OH) (sub 4) ; kaolinite-serpentine group; in low-temperature hydrothermal veins.
crook
A self-acting apparatus for running the hudges (boxes on runners) on inclines in step coalbeds.
crooked hole
A borehole that has deviated beyond the allowable limit from the vertical or from its intended course.
crookesite
A tetragonal mineral, Cu (sub 7) (Tl,Ag)Se (sub 4) ; massive or compact.
crop
a. The outcrop of a lode; or the coal of poor quality at the outcropping of a seam. See also: outcrop.
b. Deprecated syn. of outcrop. --v. To appear at the surface of the ground; to outcrop.
crop coal
a. Coal of inferior quality near the surface. CF: exposed coalfield.
b. The coal next to the roof in a seam.
crop fall
A caving in of the surface at the outcrop of the bed; caused by mining operations. Applied also to falls occurring at points not on the outcrop of the bed. Synonymous with day fall.
cropline
A line following the outcrop.
crop load
The mixture of crushing bodies, ore particles, and water being tumbled in the ball mill.
cropping
a. Coal cutting beyond the normal cutting plane.
b. Portions of a vein or other rock formation exposed at the surface.
c. See: outcrop.
d. The operation of cutting off the end or ends of an ingot to remove the pipe and other defects.
cropping coal
The leaving of a small thickness of coal at the bottom of the seam in a working place, usually in back water. The coal so left is termed "cropper coal."
crop tin
The chief portion of tin ore separated from waste in the principal dressing beneficiation operation.
cross
See: crosscut.
crossarm
a. The top member of a drill derrick of H-frame from which the sheave wheel is suspended.
b. Horizontal bar fitted between two drill columns on which a small diamond or other type rock drill can be mounted.
cross assimilation
The simultaneous exchange of material from magma to wall rock and vice versa, tending to develop the same phases in both.
crossbar
The horizontal roof member of a timber set on mine roadways, or a flat supported by props on the face. See also: beam.
cross-bedded
Having minor beds or laminae inclined to the main planes of stratification, e.g., cross-bedded sandstone.
crossbedding
a. The quality or state of being crossbedded. A crossbedded structure.
b. Lamination, in sedimentary rocks, confined to single beds and inclined to the general stratification. Caused by swift local currents, deltas, or swirling wind gusts, and esp. characteristic of sandstones, both aqueous and eolian. Syn: cross lamination.
c. Crossbedding is generally truncated by the overlying stratum. However, at the base of the crossbedded formation, the crossbedding is not truncated, but it approaches the contact with the underlying stratum in a broad tangential curve.
d. The arrangement of laminations of strata transverse or oblique to the main planes of stratification of the strata concerned; inclined, often lenticular, beds between the main bedding planes. It is found only in granular sediments.
e. Syn: inclined bedding. Should be applied to inclined bedding found only in profiles at right angles to the current direction.
cross-bladed chisel bit
Syn. for cross chopping bit.
cross-chopping bit
Bit with cutting edges made by two chisel edges crossing at right angles with the intersection of chisel edges at the center of the bit face. Used to chop (by impact) lost core or other obstructions in a borehole. Also called cross bit; cross-bladed chisel bit; cruciform bit.
cross conveyor
Any conveyor used for transporting ore or waste from one room or working place through a crosscut to an adjacent room or working place. Used principally where the cross conveyor receives ore or waste from a conveyor and delivers it to another conveyor or a car.
crosscut
a. A small passageway driven at right angles to the main entry to connect it with a parallel entry or air course.
b. A tunnel driven at an angle to the dip of the strata to connect different seams or workings.
c. A crosscut may be a coal drivage. See also: pillar-and-stall.
d. An underground passage directed across an orebody to test its width and value or from a shaft to reach the orebody. See also: level crosscut; cross.
e. A horizontal opening driven across the course of a vein or in general across the direction of the main workings. A connection from a shaft to a vein. Syn: cut-through.
f. In room-and-pillar mining, the piercing of the pillars at more or less regular intervals for the purpose of haulage and ventilation. Syn: breakthrough.
g. In general, any drift driven across between any two openings for any mining purpose.
h. A borehole directed so as to cut through a rock strata or ore vein essentially at right angles to the dip and strike of the rock strata, a vein, or a related structure.
i. See: stenton.
crossed belt
A driving belt that has a twist between the driving and the driven pulleys causing a reversal of direction.
crossed nicols
a. In optical mineralogy, an anisotropic crystal is interposed between the nicol prisms to observe its optical interference effects. The petrographic microscope is normally used with nicol prisms (or equivalent polarizing devices) in the crossed position.
b. Nicols is often capitalized (crossed Nicols). Two nicol prisms placed one in front of the other, or one below the other, and so oriented that their transmission planes for plane-polarized light are at right angles with the result that light transmitted by one is stopped by the other unless modified by some intervening body.
c. In polarized-light microscopy, the arrangement where the permitted electric vectors of the two nicol prisms are at right angles. See also: crossed polars.
crossed polars
A common standard configuration used in polarized-light microscopy with the substage polarizing filter (polarizer) permitting plane polarized light with its electric vector in an east-west direction and the above-stage polarizing filter (analyzer) permitting plane polarized light with its electric vector in a north-south direction. Under these conditions all light is absorbed by the two polars. Introduction of any anisotropic transparent material into the light path repolarizes light between the polars so as to generate interference colors and other effects visible in the microscope ocular. See also: crossed nicols.
crossed twinning
Repeated or polysynthetic twinning according to two twin laws with twin planes angled to one another and with twin domains so intimate that they appear overlapping in thin section; most notable in the feldspar and feldspathoid minerals, esp. microcline. Syn: quadrille twinning; gridiron twinning; cross-hatched twinning.
cross entry
a. An entry or set of entries, turned from main entries, from which room entries are turned.
b. A horizontal gallery driven at an angle or at right angles to a main entry.
cross face
A coal face having a general direction between end and bord line.
cross fault
A fault that strikes diagonally or perpendicularly to the strike of the faulted strata.
cross fiber
Veins of fibrous minerals, esp. asbestos, in which the fibers are at right angles to the walls of the vein. CF: slip fiber.
cross frog
A frog adapted for railroad tracks that cross at right angles.
crossgate
a. A gate road driven at an angle off the main gate in longwall mining, to form new intermediate gates or new faces inside a disturbance. Well-sited crossgates result in reduction of inby conveyors and in roadway maintenance.
b. Eng. See: crossheading.
c. York. Short headings driven on the strike end at right angles to the main gates or roads.
cross gateway
Aust. A road, through the goaf, that branches from the main gateway.
cross-hatched twinning
See: crossed twinning.
crosshead
a. A runner or framework that runs on guides, placed a few feet above the sinking bucket to prevent it from swinging too violently.
b. A beam or rod stretching across the top of something; specif., the bar at the end of a piston rod of a steam engine, which slides on the ways or guides fixed to the engine frame and connects the piston rod with the connecting rod.
crosshead guide
A guide for making the crosshead of an engine move in a parallel line with the cylinder axis.
crossheading
a. A passage driven for ventilation from the airway to the gangway, or from one breast through the pillar to the adjoining working. Also called cross hole; cross gateway; headway.
b. One driven from one drift or level across to another to improve ventilation.
c. A heading driven at an angle off the main level to cut off stalls or intermediate headings, and form new ones on the face side of the heading. Also called oblique heading; cutting-off road.
d. Eng. A road in longwall working to cut off the gateways. Syn. for crossgate; slope. Also called crossbow; crossend.
crossite
A monoclinic mineral, Na (sub 2) (Mg,Fe) (sub 3) (Al,Fe) (sub 2) Si (sub 8) O (sub 22) (OH) (sub 2) ; amphibole group with Fe (super 3+) /(Fe (super 3+) +Al)=0.3-0.7 . CF: glaucophane.
cross joint
a. A joint in an igneous rock oriented more or less perpendicular to the flow lines. Syn: tension joint.
b. A joint in sedimentary rocks that crosses more prominent joints at approximate right angles.
cross-joint fan
In igneous rock, a fanlike pattern of cross joints that follow the arching of the flow lineation.
cross lamination
a. The structure commonly present in granular sedimentary rocks that consists of tabular, irregularly lenticular, or wedge-shaped bodies lying essentially parallel to the general stratification and which themselves show a pronounced laminated structure in which the laminae are steeply inclined to the general bedding. Syn: inclined bedding; crossbedding; false bedding.
b. An arrangement of laminations, transverse to the planes of stratification of the strata concerned. They generally end abruptly at the top, but in general tend to become more or less parallel to the bedding planes below.
c. Cross-stratification with foresets less than 1 cm thick.
cross-linking agent
The final ingredient added to a water gel or slurry, causing it to change from a liquid to a gel.
cross measure
A heading driven horizontally or nearly so, through or across inclined strata.
cross-measure borehole
A borehole drilled at an angle through the rock strata generally for the purpose of combustible gases drainage.
cross-measure borehole system
See: methane drainage.
cross-measure drift
a. A development drift driven across the strata from the surface to intersect and work coal seams.
b. A development heading driven from a level in one coal seam to intersect and work upper or lower seams.
cross measure tunnel
A roadway or airway driven across pitching measures on, or nearly on, a level to reach a bed of coal or other objective, or to drain off water.
crossover
A track device that permits rail traffic to cross over another track which heads in a different direction on the same level. Signal lights are activated to avoid collision on the crossover.
cross-pit conveyors
Conveyor structure crossing the benches of open pit mines to reduce the haul distance across the pit in terrace mining operations.
cross poling
Short poling boards placed horizontally to cover the gap between runners in excavation trench timbering. See also: runner.
cross section
a. A diagram or drawing that shows features transected by a given plane; specif. a vertical section drawn at right angles to the longer axis of a geologic feature, such as the trend of an orebody.
b. An actual exposure or cut that shows transected geologic features.--Adj: cross-sectional. Also spelled: cross-section.
c. A profile portraying an interpretation of a vertical section of the Earth explored by geophysical and/or geological methods.
d. A horizontal grid system laid out on the ground for determining contours, quantities of earthwork, etc., by means of elevations of the grid points.
cross-sectional area
The area of a surface cut by a plane passing through the body and perpendicular to the long axis of the body if one exists. If not, any such area cut by a plane.
cross-sectional method
An ore reserve estimation method in which assay and other data are projected to predetermined planes and the areas of influence of the assay data are determined mainly by judgment. This method is helpful not only for ore reserve computations, but also to mine planning.
cross spread
a. A seismic spread that makes a large angle to the line of traverse; it is used to determine the component of dip perpendicular to that line.
b. A seismic spread that is laid out in the pattern of a cross.
cross-spur
A vein of quartz that crosses a lode.
cross-stone
See: andalusite; staurolite; chiastolite; harmotome.
cross stoping
See: overhand stoping.
cross-stratification
a. The minor laminations are oblique to the plane of the main stratum that they help to compose. See also: crossbedding.
b. The arrangement of layers at one or more angles to the dip of the formation. A cross-stratified unit is one with layers deposited at an angle to the original dip of the formation. Many investigators have used crossbedding and cross lamination as synonymous for cross-stratification, but it is proposed to restrict the terms crossbedding and cross lamination to a quantitative meaning depending on the thickness of the individual layers or cross strata.
crosstie
A timber or metal sill placed transversely under the rails of a railroad, tramway, or mine-car track.
cross validation
A technique for testing the validity of a variogram model by kriging each sampled location with all of the other samples in the search neighborhood, and comparing the estimates with the true sample values. Interpretation of results, however, can often be difficult. Unusually large differences between estimated and true values may indicate the presence of "spatial outliers," or points that do not seem to belong with their surroundings.
crowd
a. The process of forcing a bucket into the digging, or the mechanism that does the forcing. Used chiefly in reference to machines that dig by pushing away from themselves.
b. Used by some drillers as a syn. for overfeed. CF: overload.
c. As used by handsetters, the uneven calking of a diamond resulting in its being pinched or forced out of its intended position in a bit.
d. To place or set diamonds too closely together in the crown of a bit.
crowding
In power shovel nomenclature, crowding is the thrusting of the dipper stick forward over the shipper shaft; retracting is the reverse of crowding.
crowding battle
In froth flotation, a slanted board used to direct the rising mineralized froth toward the overflow lip of the cell.
Crowe process
The treatment of pregnant cyanide solution to remove air before the gold is precipitated with zinc dust. Also called Merrill-Crowe process.
crowfoot
a. A tool with a sideclaw, for grasping and recovering broken rods in deep boreholes.
b. Irregular or zigzag markings found in Tennessee marble. Also called stylolite.
crown
a. The curved roof of a tunnel.
b. As used by the drilling and bit-setting industries in the United States, the portion of the bit inset or impregnated with diamonds formed by casting or pressure-molding and sintering processes; hence the steel bit blank to which the crown is attached is not considered part of the crown. Syn: bit crown.
c. A timber crossbar up to 16 ft (5 m) long, supported by two heavy legs, or uprights, one at each end. Crowns may be set at 3-ft (1-m) intervals; sometimes a roof bolt is put up through the center of the crown.
d. The topmost part of a drill tripod, derrick, or mast.
e. The part of a furnace forming the top or roof.
f. The top or highest part of a mountain or an igneous intrusion; the summit.
g. The practically undisturbed material still in place and adjacent to the highest parts of the scarp along which a landslide moved.
crown block
A pulley, set of pulleys, or sheaves at the top of a drill derrick on and over which the hoist and/or other lines run. Also called crown pulley; crown wheel.
crown die
See: bit mold.
crown-in
In mining, a falling of the mine roof or a heave of the mine floor due to the pressure of overlying strata. CF: creep.
crowning
The heaving or lifting of the floor beds along a roadway to form a ridge or crown along the centerline.
crown life
See: bit life.
crown mold
See: bit mold.
crown pillar
An ore pillar at the top of an open stope left for wall support and protection from wall sloughing above.
crown tree
A piece of timber set on props to support the mine roof.
crown wheel
a. A wheel driven by a pinion, notably in the drive of a ball mill. Largest wheel of any reduction gear.
b. Syn: crown block.
croylstone
A variety of finely crystallized barite.
crucible
The hearth of a blast cupola, or open hearth furnace; a refractory vessel for melting or calcining metals, ores, etc.
crucible assay
See: assay; lead button.
crucible clays
Ball clays that are relatively refractory; used in producing crucibles that will withstand high temperatures.
crucible steel
Steel made by melting blister bar, wrought iron, charcoal, and ferroalloys in crucibles that hold about 100 lb (45 kg). This was the first process to produce steel in a molten condition, hence the product called cast steel. Mainly used for the manufacture of tool steels, but now largely replaced by the electric-furnace process.
crucible swelling number
The number that defines, by reference to a series of standard profiles, the size and shape of the residue produced when a standard weight of coal is heated under standard conditions.
cruciform bit
a. See: cross-chopping bit.
b. Percussive rock drill bit having four chisel-shaped cutting edges in the form of a cross on the face of the bit. Also called cross bit.
crucite
a. See: chiastolite; cross-stone.
b. Pseudomorph of hematite or limonite after arsenopyrite.
crud
A solid-stabilized emulsion that tends to collect at the agueous/organic interface in the settler of a solvent extraction circuit.
crude
A substance in its natural unprocessed state. Crude ore or crude oil, for example. In a natural state; not cooked or prepared by fire or heat; not altered or prepared for use by any process; not refined. Syn. for raw; crude oil.
crude anthracene
Solid product containing anthracene. Obtained on cooling the coal-tar distillate collected above 270 degrees C.
crude asbestos
Hand selected cross-vein material of longest fibres in native or unfiberized form. It comes in chunks and must be mechanically processed to develop the usefulness of the fibre.
crude mica
The crude crystals or books as extracted from the mine.
crude ore
The unconcentrated ore as it leaves the mine.
crude-ore bin
A bin in which ore is dumped as it comes from the mine.
crude sulfur
Elemental sulfur that is 99.0% to 99.9% pure and is free from arsenic, selenium, and tellurium.
crudy asbestos
Refers to asbestos that has been only partially milled, so that the fiber has not been fluffed but only separated from the rock. Most of the asbestos is still in the form of bundles of fibers like spicules.
crump
Ground movement, perhaps violent, due to failure under stress of ground surrounding underground workings usually in coal, so named because of sound produced. See also: bump.
crush
a. A species of fault in coal.
b. Breakage of supports of underground workings under roof pressure.
crushability
The relative ease of crushing a sample under standard conditions.
crush belt
A belt of intensely crushed rock.
crush border
A microscopic, granular metamorphic structure sometimes characterizing adjacent feldspar particles in granite due to their having been crushed together during or subsequent to crystallization.
crush breccia
A breccia formed essentially in situ by cataclasis, esp. along a fault. See also: cataclasite; crush conglomerate. CF: tectonic breccia.
crush bursts
Rockbursts in which there is actual failure at the face accompanied by movement of the walls.
crush conglomerate
a. A conglomerate produced by the crushing of rock strata in the shearing often accompanying folding.
b. Similar to a fault breccia, except the fragments are more rounded in a crush conglomerate.
c. See: tectonic conglomerate; pseudoconglomerate; crush breccia.
crushed gravel
The product resulting from the artificial crushing of gravel with substantially all fragments having at least one face resulting from fracture.
crushed stone
a. The product resulting from the artificial crushing of rocks, boulders, or large cobblestones, substantially all faces of which have resulted from the crushing operation.
b. Term applied to irregular fragments of rock crushed or ground to smaller sizes after quarrying. Syn: broken stone.
crushed vein
A mineralized zone or belt of crushed material. The crushing was caused by folding, faulting, or shearing.
crusher
A machine for crushing rock or other materials. Among the various types of crushers are the ball-mill, gyratory-crusher, Hadsel mill, hammer mill, jaw crusher, rod mill, rolls, stamp mill, and tube mill.
crusher feeder
In quarry industry, one who feeds broken rock into crusher after it is dumped from trucks or cars, by pushing it down a chute with a shovel or bar, or by pushing it directly into crusher from a platform. Also called crusher loader; crusher laborer; stone breaker; trap person.
crusher man
a. In the mineral and nonmineral industry, including coal, quarry products, mineral and nonmineral ores, a person who operates a machine that crushes rock or other material and regulates the flow of such material into and from the crusher to the next point of processing or use. See also: crusher; crusher feeder; crushing.
b. In quarrying, a person who operates crusher through which broken quarry rock is run to break it into crushed stone for construction work.
crusher rock
a. Term used in quarrying to describe the weathered overlying rock that occurs at most quarry operations and which is sold for use as road base.
b. The total unscreened product of a stone crusher.
crusher rolls
Steel or chilled iron roller with parallel horizontal axis and peripheries at a fixed distance apart so that rocks, coal, or other substances of greater thickness cannot pass between without crushing. Rolls may be toothed or ribbed, but for rock, including ores, the surfaces are usually smooth.
crusher-run stone
Rock that has been broken in a mechanical crusher and has not been subjected to any subsequent screening process.
crusher setting
The distance between roll faces or plates in a crusher. In the case of jaw and roll crushers, the setting controls the maximum size, and to some extent the grading of the product produced. The best setting is usually that which produces 10% to 15% of oversize pieces, which are fed back for recrushing. Gyratory breakers do not permit any marked variation in the setting or in the size of the product.
crusher stower
A machine that crushes ripping stone in headings and projects it through a pipe into gate side packs. It may also be used for filling old roadways or roof cavities. See also: pneumatic stowing.
crush gate
A gate in a development face designed to be abandoned with a view to localizing the crush effect consequent on the winning of the coal immediately above or immediately below the development face.
crushing
Size reduction into relatively coarse particles by stamps, crushers, or rolls. See also: comminution.
crushing bort
Diamond material with radial or confused crystal structure lacking distinct cleavage forms. Color is faintly milky to grayish or dark and is suitable only for crushing into grit powder or dust. The Bakwanga Mine, Republic of the Congo, is the principal source of this material. Diamond fragments from cutting establishments or recovered from waste are frequently classed as crushing bort.
crushing bortz
See: bort.
crushing cycle
The sequence of operations in crushing a material, including, e.g., the screening of the primary product and the recirculation of the screen overflow.
crushing machine
A machine constructed to pulverize or crush stone and other hard and brittle materials; a stone crusher.
crushing mill
See: stamp mill; crusher.
crushing roll
A machine consisting of two heavy rolls between which ore, coal, or other mineral is crushed. Sometimes the rolls are toothed or ribbed, but for ore their surface is generally smooth. See also: roll.
crushing strength
a. The resistance that a rock offers to vertical pressure placed upon it. It is measured by applying graduated pressure to a cube, 1 in (2.54 cm) square, of the rock tested. A crushing strength of 4,000 lb means that a cubic inch of the rock withstands pressure to 4,000 lb (111 kg/cm (super 3) ) before crushing. The crushing strength is greater with shorter prisms and less with longer prisms.
b. The pressure or load at which a material fails in compression; used for comparing the strength of walling and lining materials, such as concrete, masonry, stone, packs, etc.
c. The maximum load per unit area, applied at a specified rate, that a material will withstand before it fails. Typical ranges of value for some ceramic materials are fireclay and silica refractories, 2,000 to 5,000 psi (13.8 to 34.4 MPa); common building bricks, 2,000 to 6,000 psi (13.8 to 41.4 MPa); engineering bricks, class A, above 10,000 psi (69.0 MPa); sintered alumina, above 50,000 psi (344 MPa).
crushing test
a. A test of the suitability of stone to be used for roads or building purposes; a cylindrical specimen of the stone, of diameter 1 in (2.54 cm) and 1 in long, is subjected to axial compression in a testing machine. Syn: unconfined compression test.
b. A radial compressive test applied to tubing, sintered-metal bearings, or other similar products for determining radial crushing strength (maximum load in compression).
c. An axial compressive test for determining quality of tubing, such as soundness of weld in welded tubing.
crush line
A line along which rocks under great compression yield, usually with the production of schistosity.
crush movement
Compression, thrust, or lateral movement tending to develop shattered zones in rocks.
crush plane
A plane defining zones of shattering that result from lateral thrust.
crush zone
A zone of faulting and brecciation in rocks.
crust
a. The outermost layer or shell of the Earth, defined according to various criteria, including seismic velocity, density and composition; that part of the Earth above the Mohorovicic discontinuity, made up of the sial, or the sial and the sima. It represents less than 0.1% of the Earth's total volume. CF: tectonosphere.
b. A laminated, commonly crinkled deposit of algal dust, filamentous or bladed algae, or clots (from slightly arched forms to bulbous cabbagelike heads) of algae, formed on rocks, fossils, or other particulate matter by accretion, aggregation, or flocculation.
crustal abundance
See: clarke.
crustal plate
A portion of the Earth's crust that moves as a relatively rigid unit with respect to adjacent crustal plates that collectively cover the outermost part of the solid Earth.
crustification
a. The layering of crusts of different minerals deposited successively on the walls of a cavity.
b. Suggested for those deposits of minerals and ores that are in layers or crusts and which, therefore, have been deposited from solution.
crustified banding
A structure of vein fillings resulting from a succession, often a rhythmic deposition, of crusts of unlike minerals on the walls of an open space.
crustified vein
A vein filled with a succession of crusts of ore and gangue material.
crut
A short heading excavated into the face of a coal seam; a heading or drift across the strata, or from one deposit to another. Syn: tunnel.
crutt
N. Staff.; Som. A road or heading driven in coal measures, turned from a level, etc.
Cryderman loader
A clamshell-type loader activated by hydraulic cylinders operated from a traveling base suspended on the stage. Used in shaft sinking operations.
cryogenic switching elements
In information processing, logical switching information processing elements that utilize the variability of the transition to superconductivity as a function of magnetic field strength.
cryolite
A monoclinic mineral, Na (sub 3) AlF (sub 6) ; waxy colorless to white (disappears in water owing to low refractive index); soft; in veinlike cleavable masses in granite at Ivigtut, Greenland. Syn: Greenland spar; ice stone.
cryolithionite
An isometric mineral, Na (sub 3) Li (sub 3) Al (sub 2) F (sub 12) ; forms large colorless rhombic dodecahedra; at Ivigtut, Greenland, and the Ural Mountains, Russia.
cryology
a. In the United States, the study of refrigeration.
b. In Europe, a syn. for glaciology. See: glaciology.
c. The study of ice and snow.
d. The study of sea ice.
cryoluminescence
The low-temperature increase of weak luminescence, or its development in normally nonfluorescent material.
cryopedology
The study of the processes of intensive frost action and the occurrence of frozen ground, esp. permafrost, including the civil-engineering methods used to overcome or minimize the difficulties involved.
cryosphere
The part of the Earth's surface that is perennially frozen; the zone of the Earth where ice and frozen ground are formed.
cryoturbation
Frost action, including frost heaving.
crypthydrous
Refers to vegetable accumulations laid down on a wet substratum in contrast to those deposited under water. CF: phenhydrous.
cryptoclastic
Said of a rock of compact texture, composed of extremely small, fragmental particles that are barely visible under a microscope.
cryptocrystalline
a. Said of the texture of a rock consisting of crystals that are too small to be recognized and separately distinguished even under the ordinary microscope (although crystallinity may be shown by use of the electron microscope); indistinctly crystalline, as evidenced by a confused aggregate effect under polarized light. Also, said of a rock with such a texture. Syn: microaphanitic; microcryptocrystalline; microcrystalline; microfelsitic. CF: dubiocrystalline.
b. Said of a rock or rock texture of a crystalline rock in which the crystals are too small to be recognized megascopically. This usage is not recommended until crystallinity can be established by polarized-light microscopy or X-ray diffraction. Syn: aphanitic.
c. Descriptive of a crystalline texture of a carbonate sedimentary rock having discrete crystals with maximum diameters variously set at 1 mu m, 4 mu m, and 10 mu m.
cryptoexplosion structure
A nongenetic, descriptive term for a roughly circular structure formed by the sudden, explosive release of energy and exhibiting intense, often localized rock deformation with no obvious relation to volcanic or tectonic activity. Many cryptoexplosion structures are believed to be the result of impact of meteorites of asteroidal dimensions; others may have been produced by volcanic activity. The term largely replaces the earlier term cryptovolcanic structure.
cryptographic
a. Denoting a texture of rocks so fine that the individual constituents cannot be distinguished under a microscope. Usually the result of a cryptocrystalline intergrowth of quartz and feldspar. See also: cryptocrystalline.
b. Having a graphic texture of intergrowths too small to be resolved with a light microscope.
cryptohalite
An isometric mineral, (NH (sub 4) ) (sub 2) SiF (sub 6) ; dimorphous with bararite.
cryptohydrous
The conditions under which coal was formed. Decay under water in swamps.
cryptomagmatic
Said of a hydrothermal mineral deposit without demonstrable relationship to igneous processes. The term is little used. CF: apomagmatic; telemagmatic.
cryptomelane
a. A monoclinic mineral, K(Mn (super 4+) , Mn (super 2+) ) (sub 8) O (sub 16) ; pseudotetragonal. CF: psilomelane.
b. The mineral group coronadite, cryptomelane, hollandite, manjiroite, and priderite.
cryptomere
See: aphanite. Also spelled kryptomere.
cryptomerous
a. A very fine crystalline texture.
b. Of or pertaining to cryptomere.
cryptoperthite
Extremely fine-grained perthite with submicroscopic lamellae (1 to 5 mu m) detectable only by X-ray diffraction or electron microscopy. The K-rich host may be sanidine, orthoclase, or microcline; the Na-rich phase may be albite or analbite. CF: perthite; microperthite.
cryptovolcanic structure
A circular structure lacking evidence of shock metamorphism or of meteorite impact and therefore presumed to be of igneous origin, but lacking exposed igneous rocks or obvious volcanic features; a rock structure produced by concealed volcanic activity. Preferred term: cryptoexplosion structure.
Cryptozoic
a. Eon of hidden life. Syn. of Precambrian.
b. That part of geologic time represented by rocks in which evidence of life is only slight and of primitive forms. CF: Phanerozoic.
crystal
a. A regular polyhedral form, bounded by planes, which is assumed by a chemical element or compound, under the action of its intermolecular forces, which passing, under suitable conditions, from the state of a liquid or gas to that of a solid. A crystal is characterized first by its definite internal molecular structure and second, by its external form.
b. The regular polyhedral form, bounded by plane surfaces, which is the outward expression of a periodic or regularly repeating internal arrangement of atoms. See also: crystal face.
c. A body formed by the solidification under favorable conditions of a chemical element, a compound, or an isomorphous mixture and having a regularly repeating internal arrangement of its atoms; esp. such a body that has natural external plane faces as a result of the internal structure.
d. Quartz that is transparent or nearly so and that is either colorless or only slightly tinged. Also a piece of this material. Also called rock crystal.
e. A colorless transparent diamond.
f. As an adj., consisting of or resembling crystal. Syn. for crystalline; clear; transparent. Relating to or using a crystal.
g. A regular polyhedron exhibited by a chemical element or compound where its atomic particles assume a periodic array under suitable physical and chemical conditions. The external form is a low-energy response to the symmetry of the internal forces with each face parallel to a high-density plane of atomic particles.
h. Any solid material with a periodic internal structure. Syn: crystalline.
i. Glass of superior quality and high density and luster (resulting from inclusion of lead salts in old objects), commonly with ornamental cutting, e.g., flint glass.
j. An adj. referring to material properties, e.g., crystal structure (for internal periodicity), crystal solution (as between end members of a mineral series).
crystal aggregate
A number of crystals grown together so that each crystal in the group is large enough to be seen by the unaided eye and each crystal is more or less perfect. In gemmology, it differs from a crystalline aggregate, as a homogenous gem stone can be cut only from an individual crystal of a crystal aggregate. Syn: crystal group.
crystal axes
Imaginary lines passing through a crystal in important symmetry directions, intersecting in the origin at the center of the crystal. The axes are usually three in number, and they are chosen to act as a frame of reference by means of which the relative positions of the crystal faces can be described.
crystal axis
a. A reference axis used for the description of the vectorial properties of a crystal. There are generally three noncoplanar axes, chosen parallel to the edges of the unit cell of the crystal structure so as to be parallel to symmetry directions if possible.
b. One of three minimal noncoplanar reference lines used to describe the vectorial properties of crystalline materials. Syn: crystallographic axis.
c. A line parallel to the intersections of crystal faces. Syn: zone axis.
d. A line about which crystal symmetry appears distributed. Syn: symmetry axis.
e. A line about which a part of a crystal appears to have rotated in a fashion not permitted by the symmetry group of the crystal. Syn: twin axis. Plural: axes, pron: "aks-eez."
crystal bar
Hafnium and zirconium produced by the van Arkel and de Boer process.
crystal casts
Fillings of a cavity left by solution or sublimation of a crystal embedded in a fine-grained sediment.
crystal chemistry
The study of the relations among chemical composition, internal structure, and the physical properties of crystalline matter.
crystal class
a. One of the 32 crystallographically possible combinations or groups of symmetry operations that leave one point, or origin, fixed.
b. All minerals having the symmetry of one of the 32 point groups belong to the same crystal class. CF: point group.
crystal defect
Any deviation from perfect periodicity in a crystal structure. Some defects depend on temperature, mainly point defects; others depend on the specific history of the crystal. The presence of defects alters the physical properties of crystals. CF: Frenkel defect; point defect; line defect; volume defect.
crystal defects
Irregularities in a lattice structure that affect resistance to crushing. Microdefects are due to irregular distribution of ions. Macrodefects are incipient strain areas or discontinuities in an otherwise regular lattice. Mosaic defects are orderly blocks of regular lattice that are packed together to form a larger and imperfect particle.
crystal diamagnetism
The abnormal ratio of magnetization to the magnetizing force responsible for it, as observed in some crystals, such as those of bismuth.
crystal face
a. One of the several flat or plane exterior surfaces of a crystal. See also: crystal.
b. A planar surface developed on a crystal during its growth. Crystal faces tend to parallel planes of high lattice-point density (Bravais' law) with the result that they make rational intercepts with the crystallographic axes and may be assigned rational indices, e.g., (hkl). CF: Miller indices.
crystal flotation
The floating of lighter-weight crystals in a body of magma. CF: crystal settling. Syn: flotation of crystals.
crystal form
a. The form or shape in which crystals occur; the cube, the octahedron, and others.
b. All crystal faces related by the symmetry elements of the point group of the crystal structure belong to the same crystal form. Crystal forms are designated by the indices of the unit face enclosed in braces, e.g., hkl . Forms are closed if they singly enclose a volume and open if two or more forms are required. The terms "prism," "pyramid," "cube," "octahedron," and "tetrahexahedron" refer to crystal forms. A crystal form is ideal when all faces are the same size. Syn: crystalline form.
crystal fractionation
Magmatic differentiation resulting from the floating or settling, under gravity, of mineral crystals as they form. CF: fractional crystallization. Syn: gravitational differentiation.
crystal group
See: crystal aggregate.
crystal growth
The study of conditions for growing crystals experimentally, esp. in the control of chemical and physical properties and in application to the growth history of natural crystals. Also the microchemical and isotopic study of crystals for the physical and chemical constraints on their formation.
crystal habit
The forms typically appearing on specimens of a mineral species or group, rarely all the forms permitted by its point group. Crystal habits range from highly diverse, e.g., calcite, to almost never showing crystal faces, e.g., turquoise. In addition to describing mineral habits with form names, e.g., prismatic, pyramidal, or tetrahedral, other names for appearances are used, e.g., fibrous, columnar, platy, or botryoidal. Intergrowths are given by specific description.
crystal indices
a. Numbers or other representations that indicate the inclination of a crystal face to the crystal axes.
b. Numbers based on the rational intercepts of crystal faces with crystallographic axes. The Miller index is the reciprocal of a face's axial intercepts. Indices of crystal faces are enclosed in parentheses (hkl), crystal forms in braces hkl, crystal directions in brackets [hkl], and Bragg indices with no closure hkl. For crystals with hexagonal and trigonal symmetry, Miller-Bravais indices (hkil) may be used although the added intercept and index number are redundant (h+k+i=0). Not all mineralogists follow this usage. CF: Miller indices.
crystal lattice
a. The regular and repeated three-dimensional arrangement of atoms that distinguishes crystalline solids from all other states of matter. Essentially the regularity displayed by a crystal lattice is that of a three-dimensional mesh that divides space into identical parallelepipeds. Imagine a number of identical atoms placed at the intersections of such a mesh; then we have what is known as a simple lattice (synonymous with Bravais lattice).
b. A periodic array of points in three dimensions such that each point is in an identical point environment. Fourteen possible lattices that are used to describe the structural patterns are found in all crystalline materials by assigning an asymmetric unit to each lattice point. Syn: Bravais lattice; space lattice; direct lattice; translation lattice. CF: reciprocal lattice.
crystalliferous
Producing or bearing crystals.
crystalliform
Having a crystalline form.
crystalline
a. Made of crystal.
b. Resembling a crystal; clear, transparent, pure.
c. Pertaining to or having the nature of a crystal, or formed by crystallization; specif. having a crystal structure or a regular arrangement of atoms in a space lattice. Ant: amorphous. Said of a mineral particle of any size, having the internal structure of a crystal, but lacking well-developed crystal faces or an external form that reflects the internal structure.
d. Said of a rock consisting wholly of crystals or fragments of crystals; esp. said of an igneous rock developed through cooling from a molten state and containing no glass, or of a metamorphic rock that has undergone recrystallization as a result of temperature and pressure changes. The term may also be applied to certain sedimentary rocks (such as quartzite, some limestones, evaporites) composed entirely of contiguous crystals.
e. Said of the texture of a crystalline rock characterized by closely fitting or interlocking particles (many having crystal faces and boundaries) that have developed in the rock by simultaneous growth. A crystalline rock. Term is usually used in the plural; e.g., the Precambrian crystalline. This usage is not recommended.
f. Referring to a homogeneous solid material that has long-range periodic order of its atomic constituents. Crystalline materials distinctly diffract X-rays.
g. Referring to a rock composed of crystalline minerals, e.g., granite.
h. Referring to the texture of a rock composed of contiguous mineral crystals with or without crystal faces.
i. Referring to underlying rock with coarse texture as opposed to overlying noncrystalline or finely crystalline rock, e.g., Precambrian crystalline basement.
crystalline aggregate
An aggregate of crystalline intergrowths, such as granite, that does not show well-defined crystal forms.
crystalline flake graphite
See: flake graphite.
crystalline form
a. The external geometrical shape of a crystal.
b. See: crystal form.
crystalline grains
Minute crystals or crystalline particles which compose a granular crystalline aggregate. Distinguished from minute fiberlike crystals which compose fibrous crystalline aggregates.
crystalline granular texture
A primary texture due to crystallization from an aqueous medium, as in rock salt (halite), gypsum, and anhydrite.
crystalline limestone
a. A metamorphosed limestone; a marble formed by recrystallization of limestone as a result of metamorphism.
b. A calcarenite with crystalline calcite cement formed in optical continuity with crystalline fossil fragments by diagenesis.
c. A limestone formed of abundant calcite crystals as a result of diagenesis; specif. a limestone in which calcite crystals larger than 20 mu m in diameter are the predominant components. Examples include the crinoidal limestones whose fragments have been enlarged by growth of calcite. CF: marble.
crystalline quartz
A term used to distinguish all the varieties of quartz which are not cryptocrystalline, such as rock crystal, amethyst, citrine, cairngorm, rose quartz, tiger eye, etc.
crystalline rock
a. An inexact, but convenient term designating an igneous or metamorphic rock, as opposed to a sedimentary rock.
b. A rock consisting wholly of relatively large mineral grains, e.g., a plutonic rock, an igneous rock lacking glassy material, or a metamorphic rock.
c. The term has also been applied to sedimentary rocks, e.g., some limestones, that are composed of coarsely crystalline grains or exhibit a texture formed by partial or complete recrystallization.
crystalline structure
See: crystal structure.
crystalline tonstein
This type of tonstein contains vermicular, prismatic, or tabular kaolinite crystals and may be either light or dark in color according to the proportion of contained carbonaceous matter. Occasionally granular kaolinite may also be recognized. The crystals lie embedded in either a finely crystalline or cryptocrystalline kaolinite groundmass.
crystallinity
a. The degree to which a rock (esp. an igneous rock) is crystalline (holocrystalline, hypocrystalline, etc.).
b. The degree to which the crystalline character of an igneous rock is developed (e.g., macrocrystalline, microcrystalline, or cryptocrystalline) or is apparent (e.g., phaneritic or aphanitic).
crystallite
a. A broad term applied to a minute body of unknown mineralogic composition, or crystal form that does not polarize light. Crystallites represent the initial stage of crystallization of a magma or of a glass. Syn: crystallitic. CF: microlite; crystalloid.
b. Very small crystals in a mass or matrix.
c. A nucleus from which a crystal may grow.
d. Minute spots of double refraction in a glassy matrix.
crystallitic
Of, pertaining to, or formed of, crystallites.
crystallization
a. The process through which crystalline phases separate from a fluid, a viscous, or a dispersed state (gas, liquid solution, or rigid solution).
b. The process of crystallizing. A form of body resulting from crystallizing.
c. Formation of crystalline phases during the cooling of a melt or precipitation from a solution.
crystallization differentiation
The progressive change in composition of the liquid fraction of a magma as a result of the crystallization of mineral phases that differ in composition from the magma.
crystallization interval
a. The interval of temperature (or less frequently pressure) between the formation of the first crystal and the disappearance of the last drop of liquid from a magma on cooling. It usually excludes the late-stage aqueous fluids.
b. When referring to a given mineral, the range or the ranges of temperatures over which that particular phase is in equilibrium with liquid. In the case of equilibria along reaction lines or reaction surfaces, crystallization intervals, as thus defined, include temperature ranges in which certain solid phases are actually decreasing in amount with decrease in temperature. Syn: freezing interval.
crystallization nucleus
A small particle of any kind around which crystals begin to form when a substance crystallizes.
crystallization systems
a. The 32 possible crystal groups, distinguished from one another by their symmetry, are classified under 6 systems, each characterized by the relative lengths and inclinations of the assumed crystallographic axes. These are isometric, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic.
b. See: crystal systems.
crystallize
a. To cause to form crystals or to assume crystalline form; esp. to cause to assume perfect or large crystals. To cause to take a fixed and definite form. To become converted into crystals. To solidify by crystallizing. To deposit crystals. To become fixed and definite in form.
b. Any process by which matter becomes crystalline from a noncrystalline state. Also spelled "crystalize."
crystallized coal
See: cone-in-cone structure.
crystallizing force
a. The potentiality, or the expansive force, by which a mineral tends to develop its own crystal form against the resistance of the surrounding solid mass. This may be a differential force that causes the crystal to grow preferentially and more rapidly in one crystallographic direction than in another.
b. Expulsion of foreign constituent from a growing crystal by diffusion or mechanical displacement.
c. Expansion resulting from a crystal phase that is less dense than its noncrystalline melt phase, e.g., freezing water splitting rock or bursting pipes.
crystalloblast
A crystal of a mineral produced entirely by metamorphic processes. See also: idioblast; xenoblast. Adj: crystalloblastic.
crystalloblastesis
Deformation by metamorphic recrystallization.
crystalloblastic
a. Pertaining to a crystalloblast.
b. Said of a crystalline texture produced by metamorphic recrystallization under conditions of high viscosity and directed pressure, in contrast to igneous rock textures that are the result of successive crystallization of minerals under conditions of relatively low viscosity and nearly uniform pressure (Becke, 1903). CF: homeoblastic; heteroblastic.
c. A metamorphic texture wherein one or more mineral species grows substantially larger than the rock matrix, e.g., garnet schist. CF: porphyroblastic; granoblastic.
d. A crystalline texture owed to metamorphic recrystallization. A characteristic of this texture is that the essential constituents are simultaneous crystallizations and are not found in sequence, so that each may be found as inclusions in all the others.
crystalloblastic series
An arrangement of metamorphic minerals in order of decreasing form energy, so that crystals of any of the listed minerals tend to assume idioblastic outlines at surfaces of contact with simultaneously developed crystals of all minerals occupying lower positions in the series.
crystallochemical element
An element essential to the composition and the structure of a mineral.
crystallogenesis
The production or formation of crystals. Adj: crystallogenic.
crystallogeny
a. The science and the theory of the production of crystals.
b. That branch of materials science that deals with the formation or growth of crystals. CF: chemical mineralogy; experimental mineralogy; phase equilibria.
crystallogram
A record, photographic or electronic, of crystal structure obtained by means of X-ray diffraction. CF: Laue diagram; Laue photograph; powder pattern.
crystallographic axes
a. Three axes intersecting at right angles, the vertical one being the x axis and the two horizontal ones the y and z. The position of a crystal face is defined by the ratio of its intercepts with these axes.
b. The three noncoplanar reference vectors used to describe crystal properties. Depending upon the crystal system, these axes are not necessarily orthogonal nor of equal length, with angle alpha between axes b and c, beta between a and c, and gamma between a and b. Axes of equal length are labeled a. Where one axis is unique (hexad, tetrad, triad, or monad), convention sets it vertical and labels it c. A unique diad may be labelled c (first crystallographic setting) or b (second setting, preferred by mineralogists). By convention positive b is plotted to the right and positive a toward the observer. Some crystal classes with a unique triad may be referred to a set of three nonorthogonal axes of equal length at internal angle alpha, i.e., rhombohedral coordinates a (sub r) . In the case of a unique triad or hexad, a fourth redundant axis a (sub 3) may be added for convenience. CF: axis; coordinate system; crystal systems; fold.
crystallographic axis
See: crystal axis. CF: intercept.
crystallographic direction
a. Refers to directions in the various crystal systems that correspond with the growth of the mineral and often with the direction of one of the faces of the original crystal itself.
b. Vectors referred to as crystallographic axes. Because of crystalline periodicity, significant directions within a crystal are determined by the rational intercepts with the crystallographic axes and may be rendered in terms of Miller indices enclosed in brackets, e.g., [hkl] or [hkil].
crystallographic planes
a. Any set of parallel and equally spaced planes that may be supposed to pass through the centers of atoms in crystals. As every plane must pass through atomic centers and no centers must be situated between planes, the distance between successive planes in a set depends on their direction in relation to the arrangement of atomic centers.
b. Those planes that make rational intercepts with crystallographic axes and that may be noted by their intercept reciprocals, the Miller indices enclosed in parentheses, i.e., (hkl) or (hkil). Such planes may represent crystal faces, cleavage planes, twin planes, lattice points, or planes of atomic particles in a crystal structure.
crystallographic system
a. Any of the major units of crystal classification, embracing one or more symmetry classes.
b. See: crystal system; holohedral.
crystallographic texture
A texture of mineral deposits formed by replacement or exsolution, in which the distribution and form of the inclusions are controlled by the crystallography of the host mineral.
crystallography
a. The study of crystals, including their growth, structure, physical properties, and classification by form.
b. The science of the geometry of crystals and crystalline materials that results from symmetry generated by the periodicity of their atomic particles. See also: symmetry.
crystalloid
a. Having some or all of the properties of a crystal.
b. A microscopic crystal that, when examined under a microscope, polarizes light but has no crystal outline or readily determinable optical properties. CF: crystallite; microlite.
crystallology
The science of crystals and crystalline materials. It embraces crystallography and crystallogeny.
crystalloluminescence
The emission of light by a substance during its crystallization.
crystallothrausmatic
A descriptive term applied to igneous rocks with an orbicular texture in which early phenocrysts form the nuclei of the orbicules (Eskola, 1938). CF: isothrausmatic; heterothrausmatic; homeothrausmatic.
crystal material
Any substance possessing crystal structure but no definite geometric form visible to the unaided eye. Also known as crystalline material.
crystal mush
Partially crystallized magma; an aggregate of solid crystals lubricated by compressed water vapor.
crystal optics
a. The science that treats of the transmission of light in crystals.
b. The study and characterization of the optical properties of crystalline materials. Because each mineral species is a unique combination of chemistry and crystal symmetry, use of optical properties of minerals, both opaque and transparent, for their characterization and identification is a well-developed art.
crystal pattern
A space lattice of a crystal structure. See also: space lattice.
crystal recovery
The recovery of the original properties in a crystal that has been distorted by stress resulting from continued relief from stress, heating, or decrease in the speed of deformation.
crystal rectifier
A point contact between a metal and a crystal (such as copper and galena), or between two crystals (such as zincite and bornite). It has marked unidirectional conductivity.
crystals
a. Trade term for fourth-grade diamonds; colorless diamonds.
b. Atomic structures with long-range order. (Euhedral surfaces are not required.)
c. Geometrical forms of planar faces assumed by minerals and other crystalline materials when grown under appropriate conditions.
d. Australian syn. for drill diamonds.
crystal sandstone
a. A sandstone in which the quartz grains have been enlarged by deposition of silica so that the grains show regenerated crystal facets and sometimes nearly perfect quartz euhedra. Crystal sandstones of this nature sparkle in bright sunlight.
b. A sandstone in which calcite has been deposited in the pores in large patches or units having a single crystallographic orientation, resulting in a poikiloblastic or luster-mottling effect. In some rare sandstones with incomplete cementation, the carbonate occurs as sand-filled scalenohedra of calcite--sand crystals. See also: sand crystal.
crystal sedimentation
See: crystal settling.
crystal settling
In a magma, the sinking of crystals because of their greater density, sometimes aided by magmatic convection. It results in crystal accumulation, which develops layering. CF: crystal flotation. Syn: crystal sedimentation.
crystal solution
The replacement of one chemical element by others in a crystal structure without changing its symmetry. Syn: solid solution.
crystal sorting
The separation, by any process, of crystals from a magma, or of one crystal phase from another during crystallization of the magma.
crystal spectrometer
An X-ray spectrometer employing a crystal grating.
crystal structure
a. The periodic or repeated arrangement of atoms in a crystal.
b. The arrangement in most pure metals may be imitated by packing spheres, and the same applies to many of the constituents of alloys.
c. The periodic array of atomic particles as represented by their symmetrical disposition. Syn: crystalline structure.
crystal system
See: crystallographic system.
crystal systems
a. A classification of crystals based on the intercepts made on the crystallographic axes by certain crystal faces (or bounding planes). Syn: crystallization systems. CF: indices of a crystal face.
b. The six main symmetry groups into which all crystals, whether natural or artificial, can be classified. See also: symmetry.
c. The classification of point groups (and their associated crystal classes) and space lattices into seven (or six) symmetry systems; e.g., isometric (three equal orthogonal crystal axes), hexagonal (a unique hexad), trigonal (a unique triad), tetragonal (a unique tetrad), orthorhombic (three orthogonal diads), monoclinic (one diad inclined to an axial plane), and triclinic (no symmetry higher than a center) systems. An alternative classification of six systems assigns hexagonal and rhombohedral divisions to the hexagonal system with a different assignment of point groups having unique triads and hexads. CF: tetragonal.
crystal tuff
An indurated deposit of volcanic ash dominantly composed of intratelluric crystals and crystal fragments. CF: tuff; crystal-vitric tuff; lithic tuff; vitric tuff.
crystal-vitric tuff
A tuff that consists of fragments of crystals and volcanic glass. CF: crystal tuff; vitric tuff.
crystobalite
Crystal modification of quartz, which is formed by heating clay silica bodies at temperatures above 1,100 degrees C. Heating increases the thermal expansion and decreases the danger of crazing.