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Types of Lava Rocks: Basalt, Obsidian, Andesite

Basalt (pronounced buh-SALT) is rock composed of mostly feldspar and pyroxene. Dark in color, basalt is considered to be a fine-grained rock. Some varieties of basalt contain iron, silica, or aluminum.

Obsidian(pronounced ub-SID-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 is formed when lava cools so quickly that it does not have time to crystallize.

Like basalt, andesite (pronounced AN-deh-site) is composed of feldspar and pyroxene and is a fine grained rock. Andesite is usually light to medium gray in color. Andesite is one of the most common volcanic rocks.

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