Lab 2: Igneous Rocks Flashcards
Andesite. Colour, int/ext, and minerology
intermediate/extrusive;
aphanitic texture
plagioclase feldspar
amphibole
where is andesite formed
Stratovolcano - rapidly cooled, felsic to intermediate shallow magma or lava
Basalt colour, ext/int, texture, minerology
mafic/extrusive;
aphanitic texture
plagioclase feldspar
amphibole
pyroxene
where is basalt formed
mid ocean ridge: rapidly cooled, mafic, pillow lava - mid
shield volcano: rapidly cooled, mafic lava
Diorite colour, ext/int, texture, minerology
intermediate/intrusive;
phaneritic texture
plagioclase feldspar
amphibole
where is diorite formed
stratovolcano felsic to intermediate magma chamber - slowly cooled
Granite colour, ext/int, texture, minerology
felsic/intrusive
phaneritic texture
quartz
potassium feldspar
muscovite
biotite
plagioclase feldspar
amphibole
where is granite formed
Stratovolcano: slowly cooled, felsic to intermediate magma chamber
Gabbro colour, ext/int, texture, minerology
mafic/intrusive
phaneritic
(shiny/reflective + chunkier crystals)
plagioclase feldspar
amphibole
pyroxene
where is gabbro formed
mid ocean ridge magma chamber; slowly cooled, mafic magma
Obsidian
felsic/extrusive
glassy texture
conchoidal fracture
where is obsidian formed
Stratovolcano: very rapidly cooled, low viscosity, felsic lava
Peridotite
ultramafic/intrusive
phanertic
- can have green or be a greener black
olivine
pyroxene
plagioclase feldspar (small amount)
where is peridotite formed
upper mantle, crystallized
Pumice
felsic/extrusive
frothy
where is pumice formed
stratovolcano: very rapidly cooled, gaseous felsic lava
Rhyolite colour, ext/int, texture, minerology
felsic/intrusive
aphanitic
quartz
potassium feldspar
plagioclase feldspar
muscovite
biotite
amphibole
where is rhyolite formed
Stratovolcano:
rapidly cooled, felsic to intermediate shallow magma or lava
Scoria colour, int/ext, texture
mafic/extrusive
vesicular texture
where is scoria formed
shield volcano:
very rapidly cooled gaseous mafic lava
Volcanic Breccia
lithified ash and rock fragments
percentage of silica in felsic
> 65
percentage of silica in intermediate
55-65
percentage of silica in mafic
45-55
percentage of silica in ultramafic
<45
major minerals in igneous rocks
quartz, k-feldspar, muscovite, biotite, plagioclase feldspar, amphibole, pyroxene, olivine
vesicular texture
abundance of voids that once contained volatiles
amygdaloidal texture
secondary infillings of vesicles by minerals
frothy texture
more bubbles than rock
pyroclastic
agglomeration of broken rocks, minerals, ash, and crystallized magmatic products - volcanic breccia
aphanitic
crystals to small to identify in hand sample
phanertic
visible crystals - think of camo
phorphyritic
two stage cooling with larger crystals (phenocrysts) set in smaller crystals called the ground mass
all of the larger crystals are the same type of phenocryst
in an igneous rock how can you recognize quartz
translucent, looks smoky grey
in an igneous rock how can you recognize k-feldspar
pink
in an igneous rock how can you recognize plagioclase feldspar
white in granite/diorite, grey in gabbro/peridotite
- twinning striations
in an igneous rock how can you recognize biotite
black, can be flaked off with a knife
in an igneous rock how can you recognize amphibole
black, slender crystals, duller lustre
in an igneous rock how can you recognize pyroxene
black - not slender crystals, very vitreous
