Types of Lava Rocks
Basalt (pronounced buh-SALT) is rock composed of mostly feldspar and pyroxene. Dark in color, basalt is considered to be a fine-grained rock. There are many varieties of basalt, and some can contain iron, magnesium, silica, or aluminum.
Sometimes called volcanic glass, obsidian (pronounced ub-DID-ee-en) is semi-translucent glass that contains a large amount of silicon. Obsidian is usually black or dark gray in color, and occasionally red or brown. Obsidian that is green is rare, but does exist. When lava cools so quickly that it does not have time to crystallize, obsidian is formed.
Like basalt, andesite (pronounced AN-deh-site) is composed of feldspar and pyroxene and is a fine-grained rock. However, andesite is usually light to medium gray in color. Andesite is one of the most common volcanic rocks and can contain olivine, a green mineral.
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Copyright 2007 Trey Tombari
Last updated March 15