Volcanic rock types.

From left to right, these rocks are rhyolite, andesite, and basalt--arranged in order progressively decreasing amounts of silica.

Compare with the intrusive varieties of these rocks: photo of granite, diorite, gabbro.

On to the next slide: Mauna Loa Shield Volcano, Hawai'i
Back to the last slide: Columnar basalt.

Back to photos of volcanic rocks and features
Back to Geology photos