Volcanic glass

Volcanic glass is natural glass formed when lava cools too rapidly for crystals to grow. Obsidian is a common example.

Obsidian: A dark volcanic glass formed chiefly from silica-rich lava. It is the best-known example of volcanic glass and shows how silica-rich lava can vitrify.
Magma: Molten or partially molten rock beneath Earth's surface, often containing dissolved gases and crystals. Volcanic glass is solidified magma or lava whose melt avoided crystallizing.
Obsidian tools: Cutting and scraping implements made from fractured obsidian. Obsidian's sharp conchoidal edges made volcanic glass valuable for toolmaking.
Lipari obsidian: Obsidian from the volcanic island of Lipari in the Aeolian Islands, Italy. Its distinctive source has made it a widely traded archaeological material.
Glassy transition: The change from a flowing liquid to a rigid, disordered solid as a melt cools. Volcanic glass forms when cooling arrests melt flow before crystals can develop.
Lava: Molten rock that has erupted onto Earth's surface. Its rapid cooling at the surface commonly produces volcanic glass.
Obsidian hydration dating: A method that estimates the age of an obsidian artifact from water diffused into its surface. Hydration of volcanic glass has been used to date archaeological artifacts.
Aşıklı Höyük: A Neolithic settlement in central Anatolia occupied from the ninth millennium BCE. Its obsidian artifacts document early procurement and use of volcanic glass.
Crystallization: The formation of an ordered solid from atoms or molecules in a liquid or gas. Rapid cooling suppresses this process, preserving volcanic melt as glass.
Viscosity: A measure of a fluid's resistance to flow. Silica-rich lava's high viscosity can hinder bubbles escaping as glass forms.

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