RHYOLITE

Volcanic rock (or lava) that characteristically is light in colour, contains 69 or more per cent of silica and is rich in potassium and sodium. Low-silica rhyolite contains 69 to 74 per cent silica. High-silica rhyolite contains 75 to 80 per cent silica. Rhyolitic lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Rhyolite magmas tend to erupt explosively, commonly also producing abundant ash and pumice.