The igneous rocks of Pinnacles vary widely in their texture and color. However, they are all members of the rhyolitic group, the extrusive equivalent of the intrusively formed granitic group. As such they are dominated by quartz and feldspar. The variations are caused by differences in minor mineral content, type of extrusion, rapidity of cooling and exposure to weathering. Breccia: Reddish to grey in color, molten rock is explosively ejected with many fragments welded into a lava or tuff matrix. Breccia dominates the High Peaks and other megalithic formations.