Volcanic glass

Volcanic glass can refer to any of several types of vitreous igneous rocks. Most commonly, it refers to:

• Obsidian, a rhyolitic glass with high silica content.

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Other types of volcanic glass include:

• Pumice, which is considered a glass because it has no crystal structure.

• Apache tears, a kind of nodular obsidian.

• Tachylite (also spelled tachylyte), a basaltic glass with relatively low silica content.
• Sideromelane, a less common form tachylyte.
• Palagonite, a basaltic glass with relatively low silica content.
• Hyaloclastite, a hydrated tuff-like breccia of sideromelane and palagonite.

• Pele's hair, threads or fibers of volcanic glass, usually basaltic.
• Pele's tears, tear-like drops of volcanic glass, usually basaltic.
• Limu o Pele (Pele's seaweed), thin sheets and flakes of brownish-green to near-clear volcanic glass, usually basaltic.