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Vitrified sand is sand that has been heated to a high enough temperature as to partly melt the silicon dioxide or quartz that is the main ingredient of common sand. When sand is used to make glass, soda ash or potash are added to lower the melting point. Pure quartz melts at 1650°C. There are several natural processes that produce more or less melted sand and one man-made form:
- fulgurite is sand fused by a lightning bolt hitting sand.
- tektite is sand fused by the compressive heat of a meteor strike including moldavite a gem quality stone mined in some locations.
- frit is partially fused sand plus other chemicals in the process of glaze and glass making.
- trinitite vitrified sand forms below nuclear blasts close to a sand surface. Examples include, Trinity (nuclear test) and Emu Field.
Volcanic glass in many forms is not fused sand because it is formed from molten material.