petrography Flashcards
the identification or interpretation of framework mineralogy and textures leading to classification of wallrock as sedimentary, metamorphic, or igeous
petrography
refers to the degree of crystallinity, grain size or granularity, and the fabric
texture
consist of wholly of crystals
holocrystalline
consist entirely of glass
holohyaline
contains both crystals and glass
hypocrystalline
extremely minute, incipient crysals, provided they are birefringent
microlites
smaller, spherical, rod and hair like isotropic form
crystallite
fine grained
aphanitic or eucrystalline
coarse grained
phaneritic or dyscrystalline
very fine and undistinguishable under petrographic microscope
cryptocrystalline
very coarse grained
pegmatitic
crystals were bounded completely by crystal faces
euhedral / idiomorphic / automorphic
crystals were not bounded by crystal faces
anhedral / allotriomorphic / xenomorphic
crystals where partially bounded by crystals
subhedral / hypidiomorphic
when one mineral is surrounded by another mineral, the enclosing mineral is the younger
rules of genesis
early crystals are generally euhedral or at least more nearly than of later crystals
rules of genesis
if both large and small crystals occur together, the laeger one are the first to develop
rules of genesis
phenocryst lies in a matrix of glass
vitrophyric texture
groundmass is a dense intergrowth of quartz and feldspar
felsophyric texture
groundmass of feldspar are rectangular in form instead of slender lath crystals
orthophyric texture
phenocryst are clustered into aggregates called glomerocryst or crystal clots
glomeroporphyritic texture
glomeroporphyritic texture are formed from a process called?
synneusis
crystals, typically phenocrysts, in a igneous rock wchich contains small grains of other minerals
poikilitic texture
random plagioclase laths are enclosed by pyroxene or olivine
ophitic texture
if the plagioclase is larger and encloses the ferromagnesian minerals (olivine pyr)
subophitic texture
angular interstices between feldpar filled with glass instead of pyroxene
hyalophitic texture
a border of secondary minerals formed at the margin of a primary grain in an igneous or metamorphic rock
-common structure of hydrated ineral in volcanic rocks such as biotite or amphiboles
corona texture / reaction rim / opacitic rim
Secondary rim/coronas
kelyphitic rim
a crystal occupies the angular spaces between at least two larger crystals
intergranular texture
the angular space between larger crystals are occupied by glass or glass and small crystals
intersetal texture
texture of a groundmass of a holocrystalline igneous rock in with lath-shaped microlites are arrange in a glass-free mesostasis and are generally interwoven in irregular unoriented fashion
pilotaxitic texture
the microlites are parallel, forming flow lines along the direction of lava
trachytic texture
an intergrowth of branching rods of quartz set in a single crystal of plagioclase
myrmekitic texture
common in plagioclase with combination of zoning patterns and resorption feature
butas butas besh
seive texture
unmixing of a solid solution
exsolution
intimate intergrowth of sodic and potassic feldspar resulting from a subsolidus exsolution
perthitic solution
an intergrowth arising due to exsolution where potassic feldspar is present as blebs or lamellae with sodic feldspar
anti-perthitic texture
