dark
colors

intermediate
colors

pastel
colors

very fast cooling, glass

 obsidian with no gas
 pumice with gas

extrusive “volcanic” rocks
 erupted at surface
 cooled fast
 fine grained
 (aphanitic)

       basalt

covers ocean floor

andesite

Andes mountains

       rhyolite
    ignimbrite eruptions

porphyry has:
large-grained crystals,
dispersed in a fine-grained groundmass.

intrusive “plutonic” rocks
 cooled beneath surface
 cooled slowly
 coarse grained
 (phaneritic)

        gabbro

coarse grains

diorite

white granite

granite

often contains pink
feldspar

 
pegmatite has:
 very large crystals of quartz,
 feldspar and mica.