Glass

Glass is an amorphous solid that lacks long-range crystalline order, usually formed when a melt cools without crystallizing. Common glass is based on silica, with additives that alter its properties.

Glass transition: The temperature range in which a glass-forming liquid becomes rigid without crystallizing. Cooling through this range freezes the melt’s disordered structure into a solid.
Amorphous solid: A solid whose particles lack long-range periodic order. Glass is a familiar example of this structural class.
Tempered glass: Glass strengthened by heating and rapid cooling to create surface compression. It uses controlled stress to improve resistance to impact and thermal shock.
Obsidian: A naturally occurring volcanic glass formed when silica-rich lava cools rapidly. It demonstrates that glass can form naturally without human manufacture.
Crystal: A solid whose atoms or molecules form a repeating, long-range ordered structure. Unlike glass, a crystal has long-range structural order.
Silicon dioxide: A compound of silicon and oxygen that forms the main network in ordinary silicate glass. Its linked tetrahedra create the backbone of most commercial glass.
Silicate minerals: Minerals built from silicon–oxygen tetrahedra arranged in varied structures. Their tetrahedral units also form the structural basis of silicate glass.
Laminated glass: Glass bonded to a polymer interlayer that holds fragments together when broken. Its layered construction improves safety in vehicles and buildings.
Ancient glass: Glass produced by early societies, first as small objects and later as vessels and ornaments. Its history traces the shift from rare craft material to manufactured substance.
Glass transition temperature: A characteristic temperature range where an amorphous material changes between rigid and softer states. It distinguishes glass softening from a crystal’s sharp melting point.

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