Rocks & Sh!t
Ingrid's Dictionary of Geological, Mineralogical, and Petrographic Terms

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Note: This is a working tool intended only for my personal use. If you are not me, and you are not, please do not believe anything here without verifying it for yourself. I have included references, which are all more complete and accurate than this list. If you see any glaring errors, and you care, email me and I'll correct them.

A

ablate
to remove by cutting, abrading, or evaporating, melting; the surfaces of incoming meteorites are ablated as they fall through the atmosphere

acapulcoite
type of primitive achondrite; related to lodranites

achondrite
A stone meteorite that contains no chondrules; nonsolar composition; also differentiated stony meteorite; similar to terrestrial basalts; types include Eucrites, Howardites, Diogenites, Ureilites, Aubrites, Shergottites, Nakhlites, Chassignites [see Meteorites f]

acicular
slender, needle-like (crystal)

acidic
silicic [as opposed to basic]

adularia
variety of potassium feldspar, KAlSi3O8; probably type of orthoclase, different genetics; pseudo-orthorhombic crystal habit with rhombic cross-section; found in veins & replacement deposits; minute crystals; structurally inhomogeneous, variation in optical & structural parameters seen within single grains [DHZ 282, Kerr 302 (*pic)] [detailed notes in W. Clearwater Zeolites f]

agglutinate
aggregates of lunar soil cemented together by vesicular, flow-banded impact glass; usually < 1 mm in size; glass is black or dark brown in hand, paleto dark brown in thin section; us. heterogeneous, with schlieren or flow banding; formation requires high flux of (micro)meteorites (thus a regolith) on a surface exposed to vacuum, therefore unique to lunar surface [PM 5-11]

aggrade
To fill and raise the level of (the bed of a stream) by deposition of sediment

albite
A widely distributed white feldspar, NaAlSi3O8, that is one of the common rock-forming plagioclase group; triclinic; common in granite; sodium endmember of feldspar ternary system [see also orthoclase, anorthite]; also called soda; or sodium endmember of plagioclase series (with anorthite as opposite end)

Albite twinning
common normal twin; multiple; twin axis perpendicular to (010); recognized by composition plane || to (010) cleavage; repeated; triclinic only; [DHZ 294 (pic)]; abundant in plagioclase (useful in identifying plagioclase)

aliquot
fractional, contained an exact # of times in something else

alkaline, or alkali
basic, pH < 7; or, rich in Na or K (Rb, Cs, etc.)
Alkali feldspars are feldspars with K or Na, and very little Ca; for example, orthoclase, albite, sanidine..., basically anything except anorthite
In terms of lunar rocks, the alkali rocks are rare fragments of anorthosites comparatively rich in K and incompatible elements

allochthonous
found in a place other than where they and their constituents were formed [see allogenic]; contrast autochthonous

allogenic
describing mineral and rock constituents that were formed at some place other than the site at which they are now found [see allochthonous]

allophane
amorphous clay mineral having a variable composition of aluminum silicate, hydrated water, and traces of other minerals

alnoite (alnöite)
mafic lamprophyre characterized by mellilite; it is feldspar-free but normally contains biotite, perovskite, olivine, and carbonate in the matrix

Alpine vein
type of paragenesis... ???

Amazonian
Most recent age in Martian history, 1.8 - 0 Ga (Hartmann & Tanaka) or 3.55 - 0 Ga (Neukum & Wide) [EAA] [see also Hesperian, Noachian]

amygdule
vesicle filled with secondary mineral(s) after hydrothermal alteration

anhedral
no (mineral) faces

anhydrite
CaSO4, a colorless or white orthorhombic (+) mineral occurring in granular and compact masses; specific gravity of 2.98 and a hardness of 3.5 on the Mohs scale; an important rock-forming mineral found with gypsum, limestone, or dolomite; usually in massive aggregates of varying grain size, sometimes as parallel or radiating fibres; principle constituent of evaporites; hydrothermal alteration product of limestone & dolomite; [DHZ 470]

anorthite
calcium feldspar, CaAl2Si2O8; one endmember of feldspar ternary system [see also albite, orthoclase]; or calcium endmember of plagioclase series (with albite as opposite end); also called lime feldspar

anorthosite
type of igneous rock composed almost entirely of (calcic) plagioclase feldspar (anorthite), us. over 90% volume plag; lunar highland rock

antiperthite
intergrowth of sodium [see soda, albite] and potassium feldspars [see potash, orthoclase] in which the potassium feldspar occurs as small strings, blebs, or films; opposite of perthite

aphanitic
so fine-grained that no distinct crystals can be seen with the naked eye; ~ < 0.1 mm [contrast phaneritic]

apophyllite
KCa4Si8O20(F,OH)8H2O, a group name for white to grayish tetragonal (+) minerals with a pearly to vitreous luster, having a specific gravity of 2.3 to 2.4 and a hardness of 4.5 to 5 on the Mohs scale; occurring with zeolites in amygdules in basalts and other igneous rocks; uncommon, secondary mineral in basalts, often accompanied by zeolites, datolite, pectolite, & calcite [DHZ 275]

aragonite
calcium carbonate, different crystal structure than calcite, but same composition (polymorphic with calcite).

arenite
a consolidated sand-texture sedimentary rock irrespective of composition. Basically, sandstone. Follows composition, e.g. quartz arenite. (also arenyte)

argillaceous
clayey

astrobleme
crater (usually terrestrial)

ataxite
An iron meteorite made almost entirely of taenite; the name means "without structure" and refers to the lack of a visible Widmanstätten pattern; spindles of kamacite only visible microscopically; designated D; most bulk content Ni ≥ 15%; [compare octahedrite; hexahedrite]

Aubrite
group of stony achondritic meteorites; igneous textures, almost entirely enstatite; Ca-poor; perhaps related to enstatite chondrites

augite
type of pyroxene; high Ca; Ca(Mg, Fe)Si2O6; colorless­ - pale green in thin section, weak-mod. pleochroism, high birefringence

authigenic
of mineral and rock constituents, formed in place at the same time as, or after, the formation of the rock of which they are a part; (Also authigenous, authigenetic)

autochthonous
formed in place; contrast allochthonous

autotroph
any organism, especially photosynthetic green plants and chemosynthetic bacteria, that obtains its nutrients by synthesis from the environment, rather than by consuming other organisms. (Harcourt)


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B

basic
mafic [as opposed to acidic]

bauxite
principle ore of aluminum, mostly aluminum oxides, hydrous, clay-like

bitumin
any naturally occurring flammable substance consisting mainly of a mixture of hydrocarbons, such as petroleum or asphalt

bladed
elongated crystal, flattened like a knife blade

Boehm lamellae
any of a group of thin layers or bands of inclusions in quartz that are subparallel to the basal plane; unequivocal non-shock origin

bolide
a very bright meteor, especially one that explodes, sometimes audibly, and falls to earth in the form of meteorites; or [?] general term for impactor

breccia
coarse clastic rock composed of angular fragments of older rocks that are cemented together in a fine matrix; formed in a number of ways from a variety of materials. (An Italian word meaning "broken stones" or "rubble.") [Harcourt] [for types of breccias, see monomict breccia, polymict breccia, impact melt breccia, suevite]

bronzite
(Mg,Fe+2)2Si2O6, a green or brown, iron-containing variety of enstatite; a pyroxene with about 20% FeSiO3; comes in ortho- and clino- flavors

Bunte breccia
Type of polymict impact breccia identified at Ries crater in Germany; clasts are 25 cm - 50 m, subdivided from allocthonous blocks (>50 m) by size, flow-emplaced instead of ballistically like suevite

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C

CAI
Calcium, Aluminum-rich Inclusion; abundant in CV, and to a lesser extent CM, chondrites

calcite (also calcium carbonate)
CaCO3; (terrestrial) alteration product; very distict in optical: third order birefringence, greens & pinks, often twinned; polymorphic with aragonite.

carbonaceous chondrite
type of chondrite; very similar in composition to the Sun, less volatiles; similar spectral properties to type C asteroids

Carlsbad twinning
parallel twin; twin axis [001] (z axis); composition plane (hk0), usually (010); simple repetition; in both monoclinic & triclinic feldspars, usually only 2 individuals, sometimes up to 6 [DHZ 294, pic]; common in orthoclase, may be present in plagioclase [Kerr 292]

carotenoid
a class of red, orange, purple, and yellow pigments occurring widely in nature, synthesized in plants, and characterized by their solubility in fats; they are referred to as lipochromes when concentrated in animal fat. (Harcourt)

cataclastic
textural description; a breccia of powdered rock formed by crushing and shearing during tectonic movements; characterized by granular, fragmentary, or strained crystals

chadacryst
crystal enclosed in another crystal (the oikocryst) in a poikilitic texture; usually euhedral; or crystal foreign to rest of the (igneous) rock in which it occurs [see xenocryst]

chassignite
one of a class of Martian (probably) meteorites; Chassigny is the only known member of this class; dunite. See also sherggotites and nakhlites.

chevkinite
(Ca,Ce,Th)4(Fe+2,Mg)2(Ti,Fe+3)3Si4O22, a reddish brown to black opaque, brittle, monoclinic mineral occurring as irregular masses and prismatic crystals, having a specific gravity of 4.3 to 4.67 and a hardness of 5 to 6 on the Mohs scale; found in pumice fragments and ash from Cenozoic volcanism in the western United States; dimorphous with perrierite

chloritize
to introduce a chlorite radical into a compound

chondrite
A relatively abundant type of stone meteorite characterized by the presence of chondrules; also implies Solar composition (minus volatiles)

chondrules
Millimeter-sized glass spheres found in abundance in chondrite meteorites; existed independently prior to incorporation in meteorite; shows evidence of melting

chromite
oxide, part of spinel group [DHZ, 424]

clay
One of a member of a large group of hydrous silicate minerals. Formed by chemical weathering of igneous and metamorphic rocks. Type of clay formed is a function of the parent rock type and specific weathering conditions. E.g., a basic igneous rock with high Mg content, subjected to poor drainage and low rainfall (Mg remains in rock), will produce montmorillonite. Whereas the same rock subjected to high rainfall and good drainage (removing the Mg from the rock) will produce kaolinite. One type of clay can be produced first, and later weathered to another type of clay.
Clay minerals include kaolinite, smectite, montmorillonite, illite, halloysite, saponite, allophane.

clino-
monoclinic version of a mineral ??? [as opposed to ortho-]; literal meaning: sloping, inclined

clinoptilolite
type of zeolite, common alteration product of more silicic glasses

clinopyroxene
any monoclinic pyroxene, such as diopside, clinoferrosilite, augite, or jadeite; high birefringence compared to orthopyroxene

closure temperature
"temperature at which the observed or site partitioning of Fe and Mg is in equilibrium" [Ganguly et al. 1997]

cohenite
(Fe,Ni)3C; carbide, accessory mineral found in some iron meteorites

colloform
describing the spherical texture of a mineral deposit resulting from colloidal precipitation

colloid
a substance consisting of very tiny particles that are usually between 1 nanometer and 1000 nanometers in diameter and that are suspended in a continuous medium, such as a liquid, a solid, or a gaseous substance

comminution
the breaking down of material into a very fine powder [Penguin]

complex twins
if A & B are normal twins and B & C are parallel twins, then A & C are complex twins; B may or may not be present. twin axis lies in composition plane & is normal to a possible crystal edge [see also normal twins, parallel twins]

composition plane
- twin individuals meet along this plane; usually the same as the twinning plane [see twinning]

compressibility
- parameter that describes change in volume per unit change in pressure of a meterial; β = -ΔV / VΔP; or β = -1/v ∂v/∂P; compressability of water is .0000034 lb/ft2; reciprocal of bulk modulus

conformable
- describing continuous sequence of rock layers formed in parallel order without interruption; or the contact between such layers; contrast unconformable

consertal
- ???

cryptocrystalline
- crystals are too small to be distinguished under an ordinary microscope; contrast microcrystalline.

crystal settling
- Gravitational sinking of crystals from the liquid in which they formed, by virtue of their greater density; A type of igneous differentiation

cumulate
An igneous rock that forms by crystal settling

cumulophyric
see glomerophyric


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D

dendritic
texture like a plant, in slender divergent branches, branching, tree-like morphology.

devitrification
process by which glass (re)crystallizes; crystals which form are spherical, radiating, sometimes dendritic; most glass older than ~100 Ma has devitrified.

diabase
an intrusive, medium-grained, basaltic rock consisting principally of labradorite and pyroxene, ophitic texture is characteristic; commonly found in dikes and sills; coarser-grained than basalt; (also dolerite)

diagenesis
The process of chemical and physical change in deposited sediment during its conversion to rock; also refers to processes somewhere along the continuum between weathering (low-temperature processes) and metamorphism (high-temperature, high-pressure processes), processes which can include compaction, dissolution, cementation by precipitated minerals, and recrystallization.

diaplectic glass
glass formed by transformation of a mineral to an amorphous phase due to a pressure release; resultant glass has same composition as original mineral phase, but a lower density; differs in physical properties from glass quenched from a melt under normal conditions [Stöffler 1971]; e.g. maskelynite; disordered glass-like substance formed by shock metamorphism, without melting (solid-state reaction)

diastem
a relatively short interruption in sedimentation with little or no erosion occurring before deposition is resumed

diogenite
class of achondritic meteorite, consists primarily of Mg-rich orthopyroxene; grouped with howardites and eucrites in HED classification; [see Meteorites f on HEDs]

diopside
CaMgSi2O6; one corner of pyroxene quadrilateral [see also enstatite; ferrosilite; hedenbergite]; midway between enstatite and wollastonite

dolerite
see diabase

dolomite
CaMg(CO3)2; trigonal (-); perfect cleavage; twinning common; extremely high birefringence; similar in appearance to calcite, several chemical tests can be done to distinguish the two; associated with evaporite deposits, altered ultrabasic rocks, hydrothermal veins, metamorphosed limestones, etc.; [DHZ 489]

drusy
having many druses: a. An irregular cavity or opening in a vein or rock, having its interior surface or walls lined (encrusted) with small projecting crystals usually of the same minerals as those of the enclosing rock, and sometimes filled with water; e.g., a small solution cavity, a steam hole in lava, or a lithophysa in volcanic glass. b. A mineral surface covered with small projecting crystals; specif. the crust or coating of crystals lining a druse in a rock, such as sparry calcite filling pore spaces in a limestone. DMMRT

dunite
intrusive, ~90% olivine; minor phases include chromite, magnetite, ilmenite, & pyrrhotite


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E

endogenic
(also endogenous, endogenetic) produced or growing from within

enstatite
A mineral of the pyroxene group of silicates containing magnesium and no iron - MgSiO3; the magnesium endmember of the pyroxene system [see also wollastonite, ferrosilite, diopside, hedenbergite]; orthorhombic; also, a class of (chondritic?) meteorite.

erionite
type of zeolite

eucrite
A type of achondrite meteorite made primarily from basaltic plagioclase and (Ca-)pyroxene; three types: noncumulate, cumulate, and polymict; grouped with howardites and diogenites in HED meteorite classification; [see Meteorites f for HEDs]

euhedral
perfect crystal shapes, well-formed faces

eutectic
least possible temperature of solidification

euxinic
1. describing an environment having restricted circulation and stagnant or anaerobic conditions. 2. of or relating to the material deposited in such environments and the process of its deposition.
(Harcourt)


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F

fasciculate
having bundles, tufts, or clusters of like plant parts growing out from the same area [from biology; applies to mineral texture???]

fassaite
type of pyroxene with high Al, high Ca, high ferric/ferrousFe [DHZ 120]

ferric vs. ferrous
Fe2+ = ferrous, green; Fe3+ = ferric, red.

ferrosilite
FeSiO3; iron endmember of pyroxene system [see also enstatite, wollastonite; diopside, hedenbergite]


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G

gabbro
intrusive version of basalt; "coarse-grained intrusive igneous rock... characterized by a dark color and clinopyroxene" [Harcourt]

glomerophyric
texture in a porphyritic rock where phenocrysts are clustered in irregular groups; also cumulophyric

granite
coarse-grained plutonic rock, mostly quartz and feldspar with minor mica or other colored minerals, such as hornblende, biotite, or muscovite; rich in Si and K

granoblastic
texture of metamorphic rocks where recrystallization has formed equidimensional crystals; often, interlocking grains of a mineral meet at 120°; [see http://www.geolab.unc.edu/Petunia/IgMetAtlas/meta-micro/granoblastic.X.html for an example]

granophyre
rock dominated by quartz and feldspar intergrowth (granophyric texture); may represent the most differentiates portions of mafic intrusions; found in small sills and dikes in highly differentiated, layered intrusions; see [http://www.geolab.unc.edu/Petunia/IgMetAtlas/plutonic-micro%7F/granophyre.X.html and http://sorrel.humboldt.edu/~jdl1/web.page.images/granophyre1.html for examples]

granophyric
igneous texture, irregular intergrowth of quartz and feldspar; disconnected qu grains extinguish simultaneously under XPL, enclosed in host feldspar

granular
igneous texture where the crystals are all roughly the same size; often [but not always?] implies metamorphism. Contrast seriate.

granulitic
texture made of augite and/or olivine between laths of plagioclase [Penguin]. Also called intergranular.
"relating to a rock structure that results from the production of granular or flattened fragments in a rock by crushing...a granular igneous rock texture in which all or nearly all the components are xenomorphic" [Harcourt]
Granulitic impactites are a suite of lunar rocks which are not really granulites at all!

graupen
??? lenticular clay clast; plural of graupel? (German word for "snow pellet")


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H

halloysite
Al2Si2O5(OH)4, a white, monoclinic, clay mineral of the kaolinite-serpentine group; hydrated form; polymorphous with dickite, kaolinite, and nacrite; specific gravity of 2.0 to 2.2; hardness of 1 to 2.5 on the Mohs scale

hedenbergite
CaFeSi2O6; one corner of the pyroxene quadrilateral [see also diopside, enstatite, ferrosilite]

Hesperian
Middle age of Martian history; 3.5
1.8 Ga (Hartmann & Tanaka) or 3.8 - 3.55 Ga (Neukum & Wide) [EAA] [see also Amazonian, Noachian]

hexahedrite
type of iron meteorite made almost entirely of kamacite and named for its cubic (hexahedral) cleavage of α-Fe,Ni single crystals; Ni contents below 6%; no Widmanstätten pattern; designated H; most belong to chemical group IIA; [compare octahedrite; ataxite]

hydrothermal
\Hy`dro*ther"mal\, 1. Of or pertaining to hot water; -- used esp. with reference to the action of heated waters in dissolving, redepositing, and otherwise producing mineral changes within the crust of the globe.
2. Geology. a.Of or relating to hot magmatic emanations rich in water. b.Of or relating to the rocks, ore deposits, and springs produced by such emanations. [www.dictionary.com]
hypersthene
orthorhombic pyroxene; a pyroxene containing 22-30% FeSiO3.

hyperthermophile
An organism which thrives at very high temperatures, ~80-100 o C; see also thermophile

hypidiomorphic
of or relating to an igneous rock texture in which the individual crystals are bounded partly by crystal faces and partly by surfaces resulting from growth interference with other crystals


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I

iddingsite
alteration product of olivine; variable composition (broad term), red-brown to orange-brown, hi birefringence (1.76-1.89), includes goethite & hematite; [DHZ, 4]

ignimbrite
pyroclastic deposit; pumice, glass shards, and crystals deposited at high temperature so that resulting rocks is consolidated; same as welded tuff, although sometimes used for both welded and unwelded deposits; sometimes refers to pumice-rich deposits [PR]

illite
group of clays; most similar to micas; optical and physical properties vary, depending on hydration & impurities; weathering or (hydrothermal) alteration product, favored by alkaline & hi-Al, hi-K conditions; extremely fine-grained nature makes optical identification difficult [DHZ 260]

ilmenite
oxide, similar to hematite; (Fe, Mg, Mn)TiO3 [DHZ, 412]

immiscible
incapable of mixing or becoming homogeneous

impact melt breccia
melt-supported breccia of impact melt and clasts, compare to suevite

impactite
any rock produced during an impact (e.g. impact melt breccia, suevite, tagamite)

incompatible (element)
an element which "prefers" to be in the liquid state; last to crystallize out of a melt; e.g., most of the REEs are incompatible

indurate
to harden or become hard, as a soil lithifies into a rock

intergranular
type of interstitial texture, with pyroxene, olivine, or opaques filling the interstices between feldspar laths. Also called granulitic texture.

intersertal
of or relating to a texture of porphyritic igneous rock in which glassy or partly glassy groundmass fills the interstices between unoriented feldspar laths; [Harcourt] type of interstitial texture.

interstitial
Texture with -something- between laths of feldspar; two varieties based on what is occupying the interstices: intersertal and intergranular. [Thank you, random geo notes.]

intrafasciculate
see fasciculate. [???]

isogyre
dark cross (uniaxial) or curve(s) (biaxial) of extinction visible in interference figure [see detailed notes in Mineralogy
General f]

ITE
Incompatible Trace Elements

-ite
suffix, when added to a mineral name, meaning a rock which consists largely (>75%) of that mineral.


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J

jarosite
KFe(III)3(OH)6(SO4)2; common mineral in lower oxidized zone of ore deposits; occasionally in volcanic igneous rocks as a late hydrothermal mineral; hexagonal; optically (-); colorless-brown in section; occurs in crystal aggregates, occasionally in euhedral crystals; distinct cleavage in {0001}; very high relief; extreme birefringence; alters readily to limonite [Kerr 262; not in DHZ]


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K

kamacite
body-centered cubic α-Fe,Ni; A metal composed of a nickel-iron alloy with up to 7.5 percent nickel; a steel-gray, alpha-nickel-iron, body-centered cubic mineral, usually containing 4-7.5% Ni; hardness of 4 on the Mohs scale; specific gravity of 7.85; found in meteorites

kaolinite
Al2Si2O5(OH)4; most common type of clay, also called kandite group; forms from hydrothermal alteration of feldspars & other silicates; acid conditions favor formation; parent rocks usually silicic (granites, quartz diorites, etc.) [DHZ]; colorless or white; triclinic; polymorphous with dickite, halloysite, and nacrite

kimberlite
intrusive igneous rock, porphyritic texture, mica peridotite, w/ most abundant mineral olivine. Contains diamonds. Often forms pipes.

kink
plastic deformation feature; due to tectonics, squishing, or shock; low-pressure deformation, present in shocked rocks but not diagnostic; also "kink band"

komatiite
rare volcanic ultramafic rock composed of forsteritic olivine, pyroxene, anorthite and chromite. Displays spinifex texture from being superheated and then supercooled.

KREEP
Potassium (K) + Rare-Earth Elements (REE) + Phosphorus (P); forms at base of crust; used as noun (e.g. certain pre-mare lunar basalts) or adjective (to describe any rock rich in K, REE, and P).

K-spar
potassium feldspar, KAlSi3O8; one endmember of feldspar ternary system [see also albite, anorthite]; different forms of K-spar include sanidines (hi-T, monoclinic), orthoclase (lo-T, monoclinic), microclines (lo-T, triclinic), and adularia.


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L

labradorite
type of plagioclase

lacrustine
inland depressions or damned riverine channels containing standing water; they can be large or small areas and permanently or intermittently inundated; tranquil lake environment as opposed to large ocean or flowing water in a river, etc.

lamellar
flat, plate like individuals superimposed on and adhering to each other; describes mineral aggregate; looks like parallel to subparallel stripes in thin section

lamprophyre
igneous rock, rich in alkalis, porphyritic, lots of mafic minerals both in phenocrysts and groundmass; alnoite is one type, a minette is another

laterites
red residual soil in humid or subtropical climate, leached of soluble minerals

lechatelierite
silica glass, unstable below 1713 °C

lenticular
shaped like a lens

lherzolite
a variety of peridotite containing abundant olivine with orthopyroxene and clinopyroxene

lignite
brownish-black coal at the intermediate stage of coalification between peat and bituminous coal

lime feldspar
calcium feldspar, CaAl2Si2O8; one endmember of feldspar ternary system [see also soda (albite), potash]; pure = anorthite

lithophile
"rock-loving" element, "likes" to be in rocks [as opposed to siderophile]; officially: Said of an element with a greater free energy of oxidation per gram of oxygen than iron. It occurs as an oxide and more often as an oxysalt, esp. in silicate minerals. Examples are Se, Al, B, La, Ce, Na, K, Rb, Ca, Mn, U

lodranite
type of primitive achondrite; related to acapulcoites


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M

magnetite
Iron oxide, magnetic, a type of spinel, Fe3O4.

marl
A crumbly mixture of clays, calcium and magnesium carbonates, and remnants of shells, used as fertilizer for lime-deficient soils; designated as calcareous, clayey, or sandy

mascon
mass concentration under mare basins on moon

maskelynite
plagioclase which has been transformed by shock to glass; one type of diaplectic glass

mechanical twins
a crystalline twin formed by mechanical (plastic) deformation

melatope
dark areas around the point of emergence of the optic axis (axes) in an interference figure; dark areas at center of isogyre [see detailed notes in Mineralogy - General f]

melilite
Ca, Mg, Fe, Na, Al silicate, tetragonal; of the akermanits-gehlenite isomorphous series; found in calcium-rich basic eruptive rocks and thermally metamorphosed siliceous limestones & dolomites, abundant in alnoite [DHZ 72]

merrilite
???

mesosiderite
class of stony-iron meteorite, about 50/50 by volume of each, silicates are related to eucrites and diogenites, metal is Fe,Ni; weird mixture of "crustal" and "core" material with no mantle-y stuff; [see Meteorites f]

mesoperthite
almost a perthite???

mesostasis
the most recently formed glassy or aphanitic interstitial material of an igneous rock; submicron intergrowth which may or may not contain glass; late-forming minerals occur interstitially, forming complex mixture of fine-grained minerals and glass [Heiken et al. 1991]

metaclastic
metamorphosed clastic rock ???

metasomatism
a metamorphic process involving nearly simultaneous capillary solution and deposition, by which one mineral or mineral assemblage replaces another of different composition in the absence of melting; type of (hydrothermal) alteration

microdiastem
small version of a diastem ???

microcrystalline
crystals are too small to be seen with the naked eye, can only be seen with a microscope; contrast cryptocrystalline.

micrographic texture
intergrowth pattern of two minerals; looks like cuneiform writing; typical of a granophyre

minette
a syenitic lamprophyre consisting of biotite phenocrysts in a groundmass of orthoclase and biotite [Harcourt]

monomict
description of a breccia in which the matrix and clasts are of the same class and type; as opposed to polymict; conatins no impact melt

montmorillonites
group of clay minerals; one type of smectite; color most often pink, buff, grey, or lt. brown, many white; optical properties affected by hydration; alteration product of eruptive basic igneous rocks, usually tuff & ash, if drainage is poor & there is sufficient Mg (otherwise kaolinite), parents are usually Ca- or Na-rich, alkaline conditions

mylonite
A chert-like rock without cleavage but with a banded or streaky structure produced by extreme shearing of rocks that have been pulverized and rolled during intense dynamic metamorphism.

mylonitization
the deformation of rock produced by intense microbrecciation, resulting from the application of mechanical forces in a definite direction without any appreciable chemical alteration of granulated materials; (also mylonization)

myrmekite
special type of symplectite; vermicular quartz intergrowth with plagioclase; [see notes in Mineralogy: general f]


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N

nakhlite
one of a group of Martian (most likely) meteorites; clinopyroxenites; include Nakhla, Lafayette, Governador Valadares. See also shergottites and chassignites.

nepheline
(Na, K)(Al, Si)2O4; colorless to turbid in thin section; may have rows of inclusions; short prismatic hexagonal crystals w/ hexagonal & rectangular sections; low relief; low birefringence; alters readily to zeolites, etc.; only in soda-rich igneous rocks (nepheline syenites, phonolites, some basalts) [Kerr 322]

Noachian
Earliest age of Martian history; 3.5 - 4.6 Ga (Hartmann & Tanaka) or 3.8 - 4.6 Ga (Neukum & Wide) [EAA] [see also Amazonian, Hesperian]

norite
pyroxene (hypersthene) & plagioclase (labradorite) gabbro; coarse-grained, igneous rock, generally basaltic in composition, but with orthopyroxene as the major phase; type of lunar rock

normal twins
twin axis is normal to a possible crystal face, this face is parallel to the composition plane [see also parallel twins, complex twins]

normal zoning
trend of zoning expected for cooling magma; e.g. pyroxene gets more Fe-rich towards edges, plagioclase gets more sodic

nuée ardent
literally, "glowing avalanche" or "glowing cloud;" refers to pyroclastic flows which produce welded tuffs, specifically used for those flows which are observed [PR]


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O

octahedrite
An iron meteorite composed of taenite and kamacite, named for the octahedral (eight sided) shape of the kamacite crystal growth; show Widmanstätten pattern; further divided by width of kamacite lamellae; [PM 4-6] [compare hexahedrite; ataxite]

oikocrysts
in a poikilitic or poikiloblastic texture, the crystal that encloses the other (the chadacryst); usually anhedral

olivine bronzite
name given to H class ordinary chondrites as they are composed of olivine and bronzite

olivine hypersthene
The name given to L class ordinary chondrites as they are composed of olivine and hypersthene

ophiolite
Oceanic crust that has been thrust upward (instead of being subducted downward, as is usual) and is now in the middle of continental crust.

ophitic
an igneous rock texture that is characteristic of diabase or dolerite, which features lath-shaped plagioclase crystals partly or completely embedded in pyroxene (commonly augite) crystals; [a type of poikilitic texture; also called poikilophitic]

orogeny
The process of mountain formation, especially by a folding and faulting of the earth's crust. adj., orogenic

ortho-
orthorhombic version of a mineral??? [as opposed to clino- ]; literal meaning: straight, not sloping; in metamorphic geology, a prefix used in front of a metamorphic rock name indicating that rock derived from an igneous rock (e.g. orthogneiss) [contrast para-].

orthopyroxene
Also orthorhombic pyroxene; any of several members of the enstatite-ferrosilite series (pyroxene group) that crystallize in the orthorhombic system, and generally contain no calcium and little or no aluminum; lower birefringence than clinopyroxene, and pleochroic in PPL.

orthoclase
One type of K-spar; KAlSi3O8; potassium endmember of feldspar ternary system [see albite, anorthite]; also called potash

Ostwald ripening
Spontaneous process where lots of tiny crystals are incorporated into larger crystals. Results in a coarsening of rock texture (increase in mean grain size; decrease in number of crystals). Occurs because large crystals have lower surface-area-to-volume ratio, and are therefore energetically favorable, although formation of smaller crystals is kinetically favorable.
See Tutorial on Ostwald Ripening & references therein.


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P

palagonite
general term for hydrous, altered basaltic glass; yellow-brown, waxy, dull, resinous; [PR ch. 12]; see also detailed notes in Volcanics Project f

paleosols
ancient soils, preserved, kinda solidified [Celinda]; a stratum or soil horizon that was formed as a soil in a past geological period. [Dictionary]

pallasite
class of stony-iron meteorites; Fe-Ni metal forms a continuous framework enclosing nodules of olivine; [see Meteorites f]

para-
in metamorphic geology, a prefix added to a metamorphic rock name, indicating the rock derived from a sedimentary rock, e.g., paraschist. [contrast ortho-]

paragenesis
characteristic assemblage of minerals in a rock or an ore deposit, formed at the same time and apparently in equilibrium. (Harcourt)

paragenetic sequence
the chronological order of crystallization of minerals or mineral assemblages in a rock or an ore deposit (Harcourt)

parallel twins
twin axis is a possible crystal edge, composition plane is parallel to the twin axis and need not define a crystal face [see also normal twins, complex twins]

pedogenesis
process of soil formation

pegmatite
a light-colored igneous rock or rock group from which feldspar, mica, or gemstones are derived; characterized by very coarse grains of interlocking crystals, with typically but not exclusively granitic composition

peridotite
dark, coarse-grained plutonic rock or rock group, consisting primarily of olivine, with or without mafic minerals such as amphiboles, pyroxenes, or micas; upper mantle material

perthite
intergrowth of two minerals, specifically sodium [see soda, albite] and potassium feldspars [see potash, orthoclase] in which the sodium feldspar occurs as small strings, blebs, or films; [opposite of antiperthite]; [see detailed notes in Mineralogy - general f]

petrography
any systematic classification of igneous and metamorphic rocks on the basis of mineralogical and textural relationships, especially by means of microscopic examination [Harcourt]; especially in hand sample and thin section [Penguin]

petrology
the scientific study of rocks [Harcourt]

phaneritic
a texture with grains that are big enough to see with the naked eye; ~ > 0.1 mm grains. Further subdivided into: Fine ( < 1 mm), medium (1-5 mm), coarse (5 mm - 3 cm), and very coarse ( > 3 cm). [contrast aphanitic]

phengite
type of muscovite (mica) where Si:Al > 3:1; increase of Si is accompanied by substitution of Mg or Fe+2 for Al in octahedral sites; [DHZ 202]; sericite is also a type

phenocryst
in a porphyritic texture, larger crystals which are embedded in fine-grained groundmass; not necessarily all the same mineral

phillipsite
type of zeolite, common alt. prod. of more mafic (basaltic) glasses

phonolite
light-colored, volcanic rock, lots of feldspars; includes nephelite, haynite, etc.; thin slabs of it ring when struck, "clinkstone"

picrite
a dark, fine- to medium-grained igneous rock with abundant olivine and smaller amounts of pyroxene, hornblende, and plagioclase

piercement structure
Structures formed by the release of pressurized fluids, such as such as mud volcanoes, hydrothermal vent complexes, pockmarks and kimberlite pipes.

pigeonite
type of pyroxene, Ca-poor [DHZ, 129]

pilotaxitic
texture with a felted mass of acicular or lath-like crystals, which may show flow structure [Penguin] (See also trachytic)

pleochroic
said of a mineral which changes color in PPL when polarizer is rotated 90 degrees; diagnostic of biotite, hypersthene, hornblende, chlorite...

plessite
A mineral composed of a fine-grained mixture of kamacite and taenite that fills in the wedges between kamacite and taenite bands in iron meteorites.

poikilitic
igneous texture; large crystal(s) of one mineral (oikocryst) enclose lots of unoriented smaller crystals (chadacrysts) of another mineral; [e.g., ophitic]

poikiloblastic
texture similar to poikilitic, but formed by metamorphism and recrystallization rather than solidification from a melt

polymict
description of a breccia in which the clasts &/or matrix have differing compositions; as opposed to monomict; no impact melt

polymorph
same chemical composition, different structure under different P,T conditions; e.g., calcite and aragonite.

polysynthetic twinning
repeated twinning of crystal lamell[ae], as that of the triclinic feldspars; composed of many lathlike individuals

porphyritic
an igneous rock texture in which large phenocrysts are embedded within a fine crystalline and/or glassy groundmass

porphyry
porphyritic rock; first applied to a purple-red rock quarried in Egypt and characterized by phenocrysts of alkali feldspar; usage: rock name descriptive of the groundmass composition usually precedes the term; e.g., diorite porphyry [DMMRT]

potash
See K-spar

pseudotachylite
black vein rock superficially similar to tachylite but produced by extreme mylonitization and/or partial melting; often used descriptively, but specific meaning refers to formation of melt rocks by friction; seen at impact sites such as Vredefort and Sudbury

pyroclastic
describes clastic material ejected from volcanic vents [PR]; also called ash, tephra, etc.; pyroclastic deposits include ignimbrites, nuées ardentes, and welded tuffs.
pyrrhotite
brownish-bronze iron sulfide mineral; FeS; weak magnetic properties, also "magnetic pyrite"; FeS is approximate composition, usually contains less iron; troilite is type of pyrrhotite which is stoichiometric FeS; [DHZ 412]


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Q


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R

REE (Rare Earth Element)
chemically related, metallic elements with atomic numbers 57 - 71; special row of the periodic table; specifically, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu); most of these are incompatible elements.

regmaglypt
Depressions resembling (and called) thumbprints that are produced on the surface of some meteorites during atmospheric Itransit by material ablating (melting) off the surface.

relict
mineral, structure, or feature of a rock that persists despite processes that tend to destroy it, or remains after parts have been destroyed

rhabdite
(Fe,Ni)3P; see schreibersite; specifically refers to the morphology of small euhedral crystals in the shape of rods or platelets; once thought to be a separate mineral

rutile
common form of TiO2, reddish-brown; yellow-red-brown in PPL; hi relief, hi birefringence; occurs as minute grains in igneous rocks & needles in quartz or mica [DHZ, 415]; [see notes in Mineralogy -general f]


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S

saponite
clay mineral, hydrous silicate of Al & Mg; occurs in soft soapy amorphous masses in cavities; fills veins in serpentine & cavities in taprock

schlieren
Irregular dark or light streaks in plutonic igneous rock that differ in composition from the principal mass; Regions of a transparent medium, as of a flowing gas, that are visible because their densities are different from that of the bulk of the medium [Webster's]; streaks of fine-grained debris, more common in impact melt glass than in volcanic glass [PM 5-80]

schreibersite
(Fe,Ni)3P; a strongly magnetic, silver to tin-white, metallic, tetragonal mineral that tarnishes to brass-yellow or brown; occurs as very small euhedral tablets, plates, needles, or rods; or as coarse irregular or skeletal inclusions; specific gravity of 7.0 to 7.8; hardness of 6.5 to 7 on the Mohs scale; found in all iron meteorites. (also rhabdite)

scoria
highly vesicular basalt

seriate
texture in which crystals show a continuous range of sizes

sericite
fine-grained type of white mica (muscovite or paragonite); can be chemically same as muscovite, but often high SiO2, MgO, H20, & low K2O; occurs in silky scales with a fibrous structure; characteristic of sericite schist; replaces feldspars; can be product of hydrothermal alteration; phengite is also a type; [DHZ 202]

shergottite
class of rare achondritic meteorites, geologically youngest of any meteorites; 'S' of SNC; [see Volcanics Project f; DaG476 f; QUE94201 f]; believed to be of Martian origin; basaltic and lherzolitic; include Shergotty, Zagami, EETA79001, Que94201

sideromelane
basaltic glass, transparent. See tachylite.

siderophile
"metal-loving" elements, "like" to be in metallic form [as opposed to lithophile]; officially: Said of an element concentrated in the metallic rather than in the silicate and sulfide phases of meteorites, and probably concentrated in the Earth's core relative to the mantle and crust; or, Said of an element with a weak affinity for oxygen and sulfur, and readily soluble in molten iron; Examples are Fe, Ni, Co, P, Pt, Au

sinter
precipitate from hot or cold mineral waters; may contain silica (siliceous sinter) or calcium carbonate (travertine); specifically [?] precipitates of hydrothermal systems

size
Despite the stated opinions of some maleologists, size is important. For size terms for hand samples, see aphanitic (small) and phaneritic (big). For a discussion of "granulometric classifications," see Qualifiers, etc. recommended by the SCMR (this applies to metamorphic rocks, but it still might be handy). For igneous petrology, the terms fine-grained (< 1 mm), medium-grained (1-5 mm), and coarse-grained (>5 mm) are used.

slip face
lee side of dune (downwind), where material "slips" down as wind speed slows and material is deposited. (opposite side from stoss)

smectite
hydrous silicate of Al; greenish, ~transparent, ~gelatinous-looking; "swelling" clay (takes in water between layers); occur most commonly in fine-grained aggregates, often vermiform, lamellar, or spherulitic; birefringence higher than most kaolinites & lower than most illites; usually not identifiable optically, need other method e.g. X-ray powder, dehydration curves, etc.; weathering product of mafic rocks, hydrothermal alteration product near metalliferous veins or deposits; alkaline conditions favor formation [see montmorillonite, kaolinite] [DHZ 264]; formation favored in marine environments

soda
sodium feldspar, NaAlSi3O8; pure form = albite; one endmember of feldspar ternary system; [see also orthoclase, anorthite]

sodic
- sodium-rich, as in plagioclase

sorption
process by which one substance takes up another (by ADsorption or ABsorption)

spherulite
radiating mass of fibrous crystals in a glassy matrix

spicules
A small needlelike structure or part, such as one of the silicate or calcium carbonate processes supporting the soft tissue of certain invertebrates, especially sponges.

spinel
MgAl2O4, but also a class of minerals with the general formula A2+B23+O42- where A & B are cations such as Fe, Mg, Mn, Al, Cr, Si.... Magnetite is a spinel with Fe in both the ferric & ferrous forms. Wikipedia.

spinifex texture
hashwork of long olivine crystals; seen in komatiite

stony-irons
see mesosiderite; pallasite

stoss
the windward face of a dune (opposite side from slip face)

subhedral
describes a crystal with imperfectly developed faces

subophitic
a somewhat less-than-ophitic (poikilitic) texture, where plagioclase encloses pyroxene only partially. Penguin

subsidence
a settling/sinking down/displacement of sediments, specifically, in a vertically downward direction

subsolidus
as a melt solidifies, crystals continue to change while rock is solid but still hot; reactions occur at temperatures below melting point (below solidus)

suevite
impact breccia with fragments of impact melt (clasts); grain-supported, compare to impact melt breccia

sutured
texture in which mineral grains or irregularly shaped crystals interfere with one another, resulting in interlocking, suture-like contacts without interstitial spaces

symplectite
intergrowth of two (three) minerals; usually in high-grade metamorphosed rocks, related to decompression; myrmekite is one type; [see notes in Mineralogy - general f]

syenitic
a crystalline plutonic rock, or rock group, characterized by granular texture and consisting principally of alkali feldspar, with small amounts of plagioclase and mafic minerals, and possibly traces of quartz; it is the intrusive equivalent of trachyte [Harcourt]

syn-
prefix meaning "together" (e.g. "syndepositional")


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T

tabular
looks ~ lamellar in thin section (thin stripes); describes crystals which are tab-shaped; flat or flat-surfaced

tachylite
(also tachylyte) Variety of basaltic glass, partly or completely charged with microlites of Fe/Ti oxides, which are microcrystalline & therefore opaque in transmitted light (vs. sideromelane, which is transparent; which forms is dependent on cooling rate) [PR, 76]; black to brown or green volcanic glass of basaltic composition

taenite
face-centered cubic γ-Fe,Ni with varying Ni content (~ 27% to 65%) (may be more complex); silver-white to grayish, metallic, magnetic; found only in meteorites; specific gravity of 7.8 to 8.22; hardness of 5 to 5.5 on the Mohs scale; 27-74% nickel and a little cobalt

tagamite
impact melt rock, more specifically breccias which underlie and overlie melt sheet [Grieve et al. 1977]

tektite
A form of natural glass that, in many specimens, exhibit aerodynamic shaping caused by atmospheric passage while molten. Origin is not known, but a possibility is that they represent drops of molten silicates "splashed" out from meteorite impact events.

tetrataenite
FeNi metal, with 50±2 wt % Ni, cubic structure; see also taenite, kamacite

thermophile
an organism which thrives at high temperatures, >50o C; see also hyperthermophile

tholeiite
a silica-oversaturated basaltic rock, or rock group, containing phenocrysts of plagioclase, pyroxene, and iron oxide minerals in a glassy groundmass

tonstein
an argillaceous rock predominantly composed of the clay mineral kaolinite and some detrital and carbonaceous material; it occurs as thin bands in coal seams

trachyte
compositionally between rhyolite & phonolite, high Si (not as high as rhyolite), high Na & K (not as high as phonolite); extrusive

trachytic
volcanic texture where alkali feldspar crystals are aligned by flow [Penguin]

tridymite
SiO2, a colorless or white monoclinic pseudohexagonal or triclinic mineral occurring in minute, commonly twinned, tabular crystals and crystal aggregates in acidic volcanic rocks and stony meteorites; specific gravity of 2.26; hardness of 7 on the Mohs scale; polymorphous with coesite, cristobalite, quartz, and stishovite

troctolite
coarse-grained igneous rock, generally basaltic composition, mostly plagioclase and olivine, little to no pyroxene

troilite
brass colored sulfide of iron (FeS); common to many types of meteorites & occurs mainly in meteorites; type of pyrrhotite; non-magnetic; [DHZ 412]

twinning
The assemblage of two or more crystals, or parts of crystals, in reversed position with reference to each other in accordance with some definite law; also, rarely, in artificial twinning (accomplished for example by pressure), the process by which this reversal is brought about. Note: The relative position of the parts of a twin may be explained by supposing one part to be revolved 180 degrees about a certain axis (called the twinning axis), this axis being normal to a plane (called the twinning plane) which is usually one of the fundamental planes of the crystal. This revolution brings the two parts into parallel position, or vice versa. A contact twin is one in which the parts are united by a plane surface, called the composition face, which is usually the same as the twinning plane. A penetration twin is one in which the parts interpenetrate each other, often very irregularly. Twins are also called, according to form, cruciform, geniculated, etc. [Webster's] Present in many crystals, most typically feldspar, also calcite, dolomite, pyroxene, amphibole, etc. [see polysynthetic twinning, normal twinning, parallel twinning, complex twinning, Albite twinning, Carlsbad twinning]


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U

unconformable
relating to rock strata that do not represent part of a continuous whole with underlying (older) rocks, with respect to position, age, etc.; contrast conformable


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V

variolitic
of basic igneous rock, having a fine-grained texture characterized by varioles [Harcourt]

varioles
a small, pea-sized spherical body in igneous rock, usually composed of fanlike sprays of plagioclase or pyroxene crystals radiating outward from a central point [Harcourt]

vermicular
(also vermiform) worm-shaped

vuggy
having vugs, or small cavities in a vein or rock, usually lined with crystals of different mineralogical composition from the enclosing rock


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W

welded tuff
pyroclastic deposit, deposited at high temperature so that ash is relatively consolidated; same as ignimbrite, Nuée Ardente

whitlockite
Ca9(Mg,Fe+2)H(PO4)7; type of phosphate; a colorless, white, gray or pinkish, transparent to translucent, trigonal mineral, having a specific gravity of 3.13 and a hardness of 5 on the Mohs scale; occurs as a secondary mineral in granite pegmatites and in phosphate rock deposits, and has been identified in lunar rocks

Widmanstätten pattern
texture visible in many iron meteorites (called octahedrites) and pallasites; oriented intergrowth of kamacite and high-Ni (taenite, or more complex, variation in Ni across lamellae) lamellae; visible when polished surface is etched with nital (nitric acid in solution with ethanol)

winonaite
Rare type of achondrite meteorite - fine-grained pyroxene, Mg-rich olivine, troilite, and Ni-Fe iron. Looks like the silicate inclusions in some iron meteorites, may be related.

wollastonite
CaSiO3; represents calcic endmember of pyroxene system [see also enstatite, ferrosilite; diopside, hedenbergite], not usually shown in diagram, but used in Wo#En#Fs#; not technically a pyroxene (different structure)


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X

xenocryst
A crystal in an igneous rock that is foreign to the body of rock in which it occurs; [see chadacryst]

xenomorphic
igneous texture where crystals are not bounded by crystal faces; instead, shape is determined by " adjacent preexisting crystals" [Harcourt]


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Y

yardang
sharp, irregularly-crested ridges carved by the wind and oriented parallel to the wind. [IGGT]


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Z

zeolite
One of a group of hydrated aluminosillicates of alkali and alkaline earth metals; 2nd most common alteration product of volcanic rocks (after smectites); general formula: XuYrZnO2n x mH2O, where X=(Na,K), Y=(Ca,Sr,Ba,Mg), and Z=(Al,Si). See detailed notes in W. Clearwater f

zoning
an imperfect reaction in crystal growth between the solid and liquid phases, resulting in variations in the chemical composition within the crystal; [see normal zoning]


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Reference Codes:

DHZ = Deer, Howie and Zussman (1978) An Introduction to the Rock Forming Minerals.

DMMRT = Dictionary of Mining, Mineral, and Related Terms; http://imcg.wr.usgs.gov/dmmrt/

EAA = Encyclopedia of Astronomy and Astrophysics, http://www.ency-astro.com/

Harcourt = Harcourt Academic Press Dictionary of Science and Technology; http://www.harcourt.com/dictionary/

IGGT = Illustrated Glossary of Geologic Terms, by Steven M. Richardson, Iowa State University. http://www.geology.iastate.edu/new_100/glossary.v2.html

Kerr = Kerr (1977), Optical Mineralogy

Penguin = The New Penguin Dictionary of Geology, by P. Kearey (1996).

PM = Papike (1998) Planetary Materials, Reviews in Mineralogy 36

PR = Fisher and Schmincke (1984) Pyroclastic Rocks.