Volcanic rock types.
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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