Dacite

Close view of dacite lava from the May 1915 eruption of Lassen Peak, California

Dacite lava is most often light gray, but can be dark gray to black. Dacite lava consists of about 63 to 68 percent silica ($SiO_{2}$). Common minerals include plagioclase feldspar, pyroxene, and amphibole. Dacite generally erupts at temperatures between 800 and 1000°C. It is one of the most common rock types associated with enormous Plinian-style eruptions. When relatively gas-poor dacite erupts onto a volcano's surface, it typically forms thick rounded lava flow in the shape of a dome.

Sources

USGS Photo Glossary