GEOLOGY - ROCK [dictionary] ** DR-KNOW \ IQ-2k

ROCK (general)
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ARGILLACEOUS - A term used to describe clay-rich rocks.

BASEMENT ROCK - a thick strata of old metamorphic and igneous rock that forms the
continental crust. It is the rock layer where no sedimentary rock lies beneath.
S.A: craton, shield

CAST - Fossils formed when water containing minerals leaks into a mold. The
minerals harden to form a copy of the original structure or organism.

COBBLE - Loose particles of rock or mineral (sediment) that range in size from
64-256 millimeters in diameter.

COUNTRY ROCK - generally used to note a common regional strata being discussed or
observed

GEOPETAL STRUCTURE - a set of criteria for determining the original up direction
in sedimentary and igneous rocks.

GLACIAL DRIFT - glacial till that has been "sorted" by other processes after the
glacier has melted.

GLACIAL TILL - unsorted earth & rock deposited & transported within a glacier

LAPILLI - latin for little stones ; basically a size classification for
volcanic tephra. S.A: pyroclast

MAGMA - Usually a silicate melt (liquid) at high temperatures (650 to 1200°C)
Mixture of all the elements that make up minerals plus volatile components:
H2O, CO2, Cl, F, S , Cl, F, S ; These components form gases and will boil
off when pressure is released.

PALEOMAGNETISM - a branch of geophysics concerned with the magnetism in rocks that was
induced by the earth's magnetic field at the time of their formation.

PROTOLITH – The country rock from which a metamorphic rock was formed

REGOLITH - soil, sediment and broken rock immediately above a rock surface.

RESERVOIR ROCK - A porous and permeable subsurface rock that contains petroleum
that must be overlayed by an impermeable rock layer to keep the bouyant
hydrocarbons from floating upward. S.A: source rock

SAPROLITE - soft, thoroughly decomposed rock usually clay rich and highly porous
common to humid or tropical areas where high rates of chemical weathering
exist.

SOURCE ROCK - A sedimentary rock in which petroleum forms.

XENOLITH - a piece of rock within an igneous rock that is not part of the
original magma.

IGNEOUS ROCK
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AA LAVA - a viscous and chunky slow moving basaltic lava ; S.A: pahoehoe lava

APHANITIC - An igneous rock texture in which individual mineral grains are too
small to be distinguished with the naked eye ; S.A: phaneritic

BATHOLITH - a massive volume (greater than 100 square kilometers / 40 square miles)
of intrusive igneous rock that forms when magma solidifies at depth.

DIKEs - sheet-like igneous intrusions that cut across layers of bedrock
s.a: sill, lacolith.

IGNIMBRITE - a non-sanctioned term for igneous rocks made up of crystal and rock
fragments in a glass-shard groundmass.

LACOLITHs - igneous blister-like sills.

PAHOEHOE LAVA - is a smooth or ropy basaltic lava ; S.A: aa lava

PHANERITIC - an igneous rock texture featuring large crystals. S.A: aphanetic

PHENOCRYST - a conspicuous crystal in a porphyritic rocks

PLUTON - Any body of igneous rock that solidified below the earth’s surface.

PORPHYRITIC - an igneous rock texture containing distinct crystals or crystalline
particles embedded in a fine-grained mass.

PYROCLASTICs - the non-lava fragments associated with an explosive volcano
eruption - such as ash, pumice, obsidian and pyroclastic rocks ; SYN: TEPHRA

PYROCLASTIC FLOW - a fast moving current of hot gas and pyroclastic material.

SILL - A sheet-like igneous intrusion that parallels the plane of the
surrounding rock.

TEPHRA - SYN. PYROCLASTICs

TUFF - extensive deposits of volcanic ash.

VESCULAR - pitted texture from escaping gas bubbles

DACITE - a felsic extrusive rock intermediate in composition between andesite
and rhyolite ; S.A: Vulcanian eruption

KOMATIITE - a rare mantle-derived ultramafic volcanic rock generally of Archaean
age ; extrusive / spinifex texture / Africa

OBSIDIAN - a glassy felsic pyroclastic.

PEGMATITE - (porphyritic ?) intrusive igneous rock with large crystals

PERIDOTITE - an ultramafic (mantle) rock composed almost entirely of olivine,
with some pyroxene. Similar rocks are eclogites, which contain olivine,
pyroxene and garnet.

SCORIA - a sponge-like volcanic foam, of basaltic composition; it is spongy from
the large number of vesicles left by escaping gas in the melt.

SEDIMENTARY ROCK
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BRECCIA - a type of clastic sedimentary rock that contains angular clasts.
S.A: conglomerate

CHEMICAL SEDIMENTARY ROCK - Sedimentary rock composed of minerals that were
precipitated from water.

CLAST - An individual grain or constituent of a rock ; S.A: clastic rock,
conglomerate, breccia

CLINOTHEM - rock units generated by strata which gently prograde seawards.

CONGLOMERATE - a type of clastic sedimentary rock that contains rounded clasts.
S.A: breccia

CROSS-BEDDING - (1) The arrangement of sedimentary beds tilted at different
angles to each other, indicating that the beds were deposited by flowing
wind or water. (2) inclined beds in a sedimentary rock that were formed at
the time of deposition of currents of wind or water in the direction in
which the bed slopes downward.

CYCLOTHEM - alternating stratagraphic sequences of marine and non-marine
sediments.

DIAGENESIS - the lithification process of sediments into rock ; including all
physical, chemical, and biological steps along the way.

DEPOSITION - the laying down of rock forming minerals by natural processes.

EXTRABASINAL - rock derived from parent rock weathered outside the depositional
basin and transported into the lithification area.

INTRABASINAL - rock derived from parent rock weathered within the depositional
basin.

REGRESSION - A drop in sea level that causes an area of the land to be uncovered
by seawater which changes the sedimentary environment and changes in the
sequence stratagraphy.

SEDIMENTARY FACIES - lateral changes in depositional environment within a single
unit.

SEDIMENTARY STRUCTURES - patterns formed by depositional and environmental
processes that are often preserved in strata. These include the grading
(sorting by size) of sediment grains, ripple marks, cross-beds and animal
tracks. They are used by geologists to infer the environment into which the
sediments were deposited

SEDIMENT - a solid fragment of silt, sand, gravel, or fossil transported and
deposited by water, wind, or ice.

TRANSGRESSION - A rise in sea level relative to the land which changes the
sedimentary environment and changes in the sequence stratagraphy.

TURBIDITY CURRENT - A fast-flowing current that moves down a slope depositing
suspended sediments over the floor of a body of water. Underwater landslide.

ANTHRACITE - hard coal.

BITUMINOUS COAL - primary source of industrial heat generating coal.

DOLOSTONE – a magnesia-rich sedimentary rock resembling limestone, only fizzes
in HCl when scratched.

METAMORPHIC ROCK
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ACF DIAGRAM - a triangular diagram showing a simplified molecular character for
metamorphic rock

AMF DIAGRAM - a triangular diagram showing a simplified molecular character for
pelitic metamorphic rock ; old term form mudstone

AUGEN - Augen are relatively large, eye-shaped mineral grains in certain types
of metamorphic rocks.

CATACLATIC ROCK - a metamorphic rock commonly associated with fault zones of high
pressure and low-temperature

CONTACT METAMORPHISM - Metamorphism caused by heat from an igneous intrusion.

CRENULATION - a fabric or wavy texture in metamorphic rocks.

DYNAMIC METAMORPHISM - orogenic movement and differential stresses that crush,
shear, and grind the parent rock into a new assemblage of minerals at
relatively low temperatures and high pressures.

FOLIATION – Pressure induced layering of metamorphic rocks as noted in the
parallel alignment of minerals

METAMORPHIC FACIES - zones of metamorphic rock wherein the metamorphic mineralogy
suggests different pressure and temperature conditions than adjacent zones.

PROGRADE METAMORPHISM - changes in mineral assemblage and mineral composition that
occur during burial and heating.

REGIONAL METAMORPHISM - occurs over very large areas, such as deep within the
cores of rising mountain range or along subduction zones, and can be
accompanied by folding and shearing of rock layers.

RETROGRADE METAMORPHISM - changes in mineral assemblage and mineral composition
that occur during uplift and cooling .

S-C FABRIC - a metamorphic fabric / foliation formed by the intersection of shear
surfaces of rocks undergoing dynamic metamorphism ; very common in mylonites ;

TECTONITE - a class of metamorphic rock formed by tectonic forces

FAULT BRECCIA [tectonite] - formed in zones of brittle deformation

GOUGE [tectonite] - has no cohesion and is normally unconsolidated ;
Cf. fault gouge

MYLONITE [cataclastic tectonite-foliated] - formed in zones of ductile deformation
at approx. 9km deep.

AMPHIBOLITE - [ foliated coarse-grained ][ hornblende group ][parent - gabbro]
composed mainly of green, brown, or black amphibole minerals and plagioclase
feldspar.

QUARTZITE – [ nonfoliated ] formed from sandstones rich in quartz
sand grains and quartz cement