tridümiit

Tridymite is a high-temperature polymorph of silica (silicon dioxide, SiO2). It is one of the three common polymorphs of silica, the others being quartz and cristobalite. Tridymite is stable at temperatures between approximately 870 and 1470 degrees Celsius at atmospheric pressure. However, it can persist metastably outside of its stability field. Its crystal structure is complex and can exist in several different forms, or polytypes, depending on the temperature. The most common form is hexagonal. Tridymite is less dense than quartz but denser than cristobalite. It typically forms as small, tabular, orthorhombic crystals, though these can appear pseudo-hexagonal. It is often found intergrown with cristobalite. Tridymite is a relatively rare mineral in terrestrial igneous rocks, but it is more commonly found in felsic volcanic rocks that have undergone rapid cooling. It is also found in meteorites and has been identified in lunar samples. In industrial applications, tridymite is significant in the refractory industry, particularly in silica refractories used in furnaces. Its presence can affect the thermal expansion and stability of these materials.