Igneous Rock Identification Data Sheet
Name
Type
Geological Environment
extrusive (volcanic)
Foliation &
Grain Size
no layering
continental crust
fine grained
extrusive (volcanic)
no layering
forms in mountain building
zones at continent-ocean
boundaries
fine grained
basalt
extrusive (volcanic)
no layering
fine grained
granite
oceanic crust
volcanic island arcs
mid plate hot spots (Hawaii)
intrusive (plutonic)
continental crust
and high grade metamorphic
areas where rock has remelted into granitic diapirs.
coarse grained
rhyolite
andesite
no layering
pergmatites (very
coarse grained
rocks)
no layering
diorite
intrusive (plutonic)
coarse grained
gabbro
forms in mountain building
zones at continent-ocean
boundaries
intrusive (plutonic)
oceanic crust
volcanic island arcs
mid plate hot spots (Hawaii)
coarse grained
no layering
Mineral
Composition
quartz, orthoclase,
muscovite,
plagioclase,
hornblende, biotite
plagioclase,
amphibole,
usually biotite, may
have quartz or
pyroxene
plagioclase,
pyroxene,
amphibole, and
possible olivine
quartz, orthoclase,
muscovite,
plagioclase,
hornblende, biotite
plagioclase,
pyroxene,
amphibole, and
possible olivine
plagioclase,
pyroxene,
amphibole, and
possible olivine
Chemical
Composition
felsic (acidic)
Colour
and Other
light colour – grey
high SiO2(>63%),
Al2O3, K, Na and
other alkali elements
intermediate
can forms tuffs
(volcanic ash that is
cemented together)
medium colour
SiO2(55 -63%),
medium Mg, Fe, Ca
medium alkali (Na,K)
mafic (basic)
dark colour
low SiO2(45 -55%),
high Mg, Fe, Ca
low alkali (Na,K)
felsic (acidic)
green, black
high SiO2(>63%),
Al2O3, K, Na and
other alkali elements
red/orange, white and
black
intermediate
medium colour
light colour
SiO2(55 -63%),
medium Mg, Fe, Ca
medium alkali (Na,K)
mafic (basic)
dark colour
low SiO2(45 -55%),
high Mg, Fe, Ca
low alkali (Na,K)
green, black, grey
peridotite
intrusive or rarely extrusive
no layering
pyroxene and olivine
coarse grained
obsidian
extrusive (volcanic)
no layering
glass (no grains
or crystals formed
– rapid cooling)
volcanic glass – no
minerals visible
ultramafic
very low SiO2(<45%)
high Mg and Fe
any composition
green
Dunite – only olivine
brown, green, black,
grey