igneous compositions and rocks Flashcards
how much silica in silicic rocks
66-75%
how much silica in intermediate rocks@?
52-66%
how much silica in mafic rocks?
45-52%
how much silica in ultra mafic rocks?
> 45%
what does grain size tell you in igneous rocks?
rate of cooling
what does composition and colour (mafic/silicic etc..) tell you about igneos rocks
silica content
what does texture tell you about igneous rocks?
origin (where it formed)
what is the relationship between silica % and viscosity?
the more silica, the more viscous
COARSE SILICIC ign ROCK
granite (and granodiorite)
TEXTURE: porhyritic/equigranular
FINE SILICIC ign ROCK
rhyolite
TEXTURE; flow banded
GLASSY SILICIC ign ROCK
obsidian
TEXTURE: glassy (with choncoidal fracture)
pumice
TEXTURE: vesicular
what do silicic magmas contain?
mostly quartz
plagioclase + potash ? feldspar
muscovite and biotite mica
what temp do silicic magmas cool and solifdify at?
lower temps 600-900C
what temp does intermediate magma solidify at?
higher temp than a silicic magma
where are andesites (fine intermediate) common at?
convergent plate margins
FINE INTERMEDIATE ign rock
andesite
COARSE INTERMEDIATE ign rock
diorite
FINE MAFIC ign rocks
basalt
MEDIUM MAFIC ign rock
dolerite
COARSE MAFIC ign rock
gabbro
texture of andesite
vesicular, amygdaloidal, porphyriitic OR equigranular
texture of diorite
equigranular + porphyritic
`texure of basalt
vesicular or amygdaloidal or porphyrictic or equigranular
texture of dolorite
porphyritic or equigranular
texture of gabbro
equigranular
example of an ultra mafic rock (most common)
peridotite
