Pinnacles National Park
This view of rhyolite cliffs is near the falls along the Condor Gulch Trail. Rhyolite is a volcanic rock that is similar to granite in composition (mostly quartz and feldspar) but because if formed from rapidly-cooling lava ejected from the volcano, mineral crystals are too small to see. The volcanic rocks in Pinnacles National Park range in composition from rhyolite, dacite, to andesite (silica-rich [felsic] to intermediate mafic rocks [containing some dark iron and magnesium rich minerals]). Rock textures include breccia (rock composed of explosively ejected volcanic rock fagments welded together from the heat of an eruption), flow-banded lava rock (preserving the texture of flowing molten rock before cooling), pumice lapili tuff (welded volcanic ash and sand-sized volcanic debris), and perlite (an opaque form of volcanic glass formed from rapidly cooled lava) (NPS, [2010]).
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Last modified: 10/21/2010