Vitreous

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Vitreous refers to a material in an amorphous, glassy state (in contrast to a crystalline state). In such a state, the constituent atoms do not exhibit the long-range order that is characteristic of crystals. However, they still exhibit short-range order -- the separation of atoms and/or the lengths of covalent bonds are very close to their typical equilibrium distances. The creation of a vitreous material by supercooling or by addition of additives prior to cooling is called vitrification.

Under certain conditions, vitreous materials may begin to rearrange themselves into crystals. This process is referred to as devitrification. Natural volcanic glass, obsidian, will de-vitrify or crystallize over extended periods of geologic time. Devitrification can also occur in glass items that are regularly washed in dishwashers due to the chemicals involved in their detergents.^[1]

Other uses

When applied to whiteware ceramics, vitreous means the material has an extremely low permeability to liquids, often but not always water, when determined by a specified test regime. The microstructure of whiteware ceramics frequently contains both amorphous and crystalline phases.
A vitreous luster in mineralogy refers to a glassy luster or sheen of a mineral surface. The minerals quartz and fluorite exhibit a vitreous luster.
The vitreous humour (British spelling) or vitreous humor (U.S. spelling) is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates.