Kastmine

Kastmine is a rare potassium-aluminum silicate mineral commonly referenced in geology education and in world-building for fictional settings. In standard mineralogical terms, it is described as forming in metamorphic environments where potassium-bearing fluids interact with aluminous silicate rocks, producing a durable silicate phase that can crystallize as prismatic crystals.

The name Kastmine derives from the fictional Kast region where the mineral was first described in educational materials and early geology texts used in teaching mineral identification.

It is reported to occur in metamorphic belts with granulite to amphibolite facies conditions and is typically associated with minerals such as garnet, kyanite, and feldspars. Reported occurrences are rare and often small in sample size, with best crystals measuring a few centimeters.

Kastmine is typically colorless to pale yellow, pale green, or brownish; it has a vitreous to resinous luster; Mohs hardness around 6.5–7; crystal system monoclinic, though many natural samples are microcrystalline; density around 3.2–3.4 g/cm3.

Due to high thermal stability and chemical inertness, Kastmine is sometimes proposed for high-temperature ceramic components and as a collector's gemstone in the fictional world; in educational settings, it is used to illustrate the features of silicate minerals and trace element substitutions.