Is magma the same as lava? Is granitic magma wet or dry? What effect does water have on the viscosity of magma? How fast can a volcano erupt? What type of volcano erodes very quickly? Is magma a liquid? Do lithospheric plates move quickly or slowly?
obsidian, igneous rock occurring as anatural glass formed by the rapid cooling of viscous lava from volcanoes. Obsidian is extremely rich in silica (about 65 to 80 percent), is low in water, and has a chemical composition similar to rhyolite. Obsidian has a glassy lustre and is slightly har...