25 terms

Earth Materials Textures

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Phaneritic
visible grains -> cooled slowly underground (plutonic)
Aphanetic
no grains visible -> cooled quickly above ground (volcanic)
Poikilitic
small randomly oriented grains of a mineral are included within another mineral. Texture applied to Igneous rocks. In metamorphic rocks the larger mineral is called a Poikioblast
Adcumulus
interstitial melt exchanges with magma chamber, less extreme fractionation (more interstitial space)
Orthocumulus
Little to no exchange between interstitial melt and magma chamber, more extreme fractionation (less interstitial space)
Porphyritic
two distinct grain sizes (usually coarse phenocrysts in a fine-grained groundmass)
Equigranular
all grains are approximately equal
Vesicular
cooled with vesicles of volatiles, riddled with holes
Amygdular
Vesicles are filled with secondary minerals, often quartz, calcite, or chlorite
Pegmatic
a coarsely crystalline granite or other igneous rock with crystals several centimeters to several meters in length, incompatible elements become concentrated in melt till end of crystallization (i.e.: spodumene and corundum)
Glassy
if you don't know this you're dumb. instantly cooled
Pyroclastic
rock made of cemented pyroclastic flow. Includes tuffs and pyroclastic breccias
Welded
tuff that was so hot it underwent some remelting, wavy layered looking texture
Trachytic
lath shaped feldspar crystals floating in igneous groundmass, sub-parallel alignment of crysts can indicate flow
Felty
tiny lath shaped crystals, looks like static in thin section, can show preferred direction -> indicates flow
Perthitic
Potassium rich feldspar (dark) with lamellae of sodium feldspar (light) (antiperthite is the opposite)
Granophyric
intergrown feldspar and quartz crystals in a medium- to fine-grained groundmass
Spinifex
texture distinctive to Komatiite, plate-like crystals radiating in random directions
granoblastic
metamorphic texture where three crystals all intersect at 120 degree angles
porphyroblastic
the metamorphic equivalent of phenocryst, grown within the groundmass
metamorphic foliation
repetitive layering in metamorphic rocks, evidence of directional stress
slaty cleavage
extremely closely spaced, parallel planes of weakness that give a rock like slate its ability to split into very thin, platy layers
shistocity
medium to large, flat, sheet-like grains in a preferred orientation. It is defined by having more than 50% platy and elongated minerals (micas, chlorite, talc, hornblende)
gneissic banding
layers that appear as bands in cross section, caused by metamorphism by temp and pressure, darker bands are more mafic, lighter bands are more felsic
crenelation reaction rims
rim around a mineral that reacted with surrounding melt
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