glassy

Glassy is an adjective describing objects or materials that resemble glass in appearance or properties. A glassy surface is typically smooth, shiny, and reflective, often transparent or translucent. The term is used in several disciplines to denote different but related ideas of rigidity and clarity.

In materials science, "glassy" refers to an amorphous solid—one lacking a long-range crystalline order. Glasses such as silica glass and many polymers become glassy below their glass transition temperature (Tg), at which they are hard and brittle but not crystalline. Glasses do not have a single melting point; instead they gradually soften as temperature increases. Quenching a melt rapidly can produce a glassy state; slow cooling can allow crystallization.

In geology and volcanology, volcanic glass describes rocks formed by rapid cooling of lava, preventing crystals from forming. Obsidian is a well-known natural glass. Glassy textures also appear as microcrystalline or amorphous components in some volcanic rocks, and conchoidal fracture is a characteristic of glassy materials.

Glassy can also describe a human or animal's eyes that appear dull, unfocused, or devoid of expression, as in "glassy-eyed." It is used metaphorically to suggest detachment or shock, often after anesthesia or fatigue.

In cultural usage, the term is sometimes applied to glazes, coatings, or glass-like finishes on objects.