Volcanic rock with 68% to 72% silica (see silica). Rhyodacitic lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Rhyodacite magmas tend to erupt explosively, commonly also producing abundant ash and pumice.

Siphon Draw - Superstitions made of Rhyodacite














The Superstition Mountains near Phoenix, Arizona are comprised, in large part, of rhyodacite.