Dacite

Volcanic rock with about 64% to 68% silica. (see silica). Dacite lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Dacitic magmas tend to erupt explosively, thus also ejecting abundant ash and pumice.

Dacite Cliffs at the entrance to Peralta Canyon, Superstition Wilderness