Common types of volcanic rock

name silica content (percent) major minerals colour approximate density with no voids (grams per cubic cm)

basalt 45-53 Ca feldspar, pyroxene, olivine dark gray 3.0

andesite 53-62 CaNa feldspar, pyroxene, amphibole medium gray 2.9

dacite 62-70 Na feldspar, amphibole, biotite, quartz light gray* to tan 2.8

rhyolite 70-78 K, Na feldspars, quartz, biotite light gray* to pink 2.7

*Obsidian glass can be dark gray to black.