MARK A. SCHNEIDER / SCIENCE PHOTO LIBRARY MARK A. SCHNEIDER / SCIENCE PHOTO LIBRARY
Hand sample of Basalt, an extrusive igneous rock composed of calcic plagioclase feldspar, pyroxine, and occasionally olivine. Accessory minerals are sometimes visible. Basalt has an aphanitic (microcrystalline) texture; the mineral grains are too small to be seen by the naked eye.
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