Some information on geology

There are three types of lavas formed by volcanoes. Mafic, Intermediate, and Felsic.

Mafic(Basaltic)
%SiO2: < 50%
%FeMg: 4%
Temp: up to 1500C
Viscosity: Low
Eruptive Behavior: gentle
Distribution: divergent plate boundries, hot spots, convergent plate boundries

Intermediate(Andesitic)
%SiO2: ~60%
%FeMg: ~3%
Temp: ~1000C
Viscosity: Intermediate
Eruptive Behavior: explosive
Distribution: convergent plate boundries

Felsic(Rhyolitic)
%SiO2: >70%
%FeMg: 2%
Temp: 700C
Viscosity: High
Eruptive Behavior: explosive
Distribution: hot spots in continental crusts (Yellowstone National Park)