mikroklin

Mikroklin, or microcline, is a potassium feldspar mineral with the chemical formula KAlSi3O8. It is the triclinic polymorph of potassium feldspar, distinct from orthoclase and sanidine, and represents the low-temperature form stable in many rocks. Mikroklin is a common constituent of granitic rocks, granite pegmatites, and alkali-rich metamorphic rocks, and it can occur as an alteration product in some hydrothermal systems.

Crystallography and properties: Mikroklin forms triclinic crystals and has a vitreous luster. It is typically white, pink, or greenish in color and has a Mohs hardness of about 6. It cleaves in two directions at near 90 degrees. The crystal habit ranges from euhedral prisms to granular aggregates.

Notable features: Mikroklin is well known for its exsolution lamellae with albite, which produce a grid-like or tartan twinning pattern visible in polished sections or under polarized light. This grid twinning is a characteristic diagnostic feature and helps distinguish mikroklin from other feldspars such as orthoclase.

Geological significance and uses: As a major rock-forming mineral, mikroklin is a principal reservoir of potassium in the continental crust. It is widely used in ceramics and glassmaking, and it also occurs as a decorative stone in various architectural and ornamental applications.