Some information on geology

There are three(3) 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)