Albite

Albite is the sodium-rich end-member of the plagioclase feldspar series, which ranges continuously from albite (sodium) to anorthite (calcium). Its name comes from the Latin for "white," reflecting its typical pure white to colorless appearance.

It is an extremely common rock-forming mineral, found in igneous, metamorphic, and some sedimentary rocks. Albite shows the characteristic plagioclase twinning that produces fine parallel striations on cleavage surfaces.

Several notable varieties exist, including the platy, bladed cleavelandite and peristerite, an albite-oligoclase intergrowth that displays a bluish moonstone-like sheen. Albite is also a key component in many granitic pegmatites and is associated with valuable gem minerals.

Albite forms in a wide range of geologic settings. It crystallizes late from sodium-rich granitic magmas and is especially abundant in granite pegmatites, where it can occur as the platy variety cleavelandite lining pockets alongside tourmaline, beryl, and lepidolite.

It is also a product of low- to medium-grade metamorphism, forming in albite schists and during the process of albitization, where sodium-rich fluids replace earlier feldspars. Notable localities include pegmatites in Brazil, Pakistan, Madagascar, and the United States. As the stable sodic plagioclase at lower temperatures, albite is widespread in many continental crustal rocks.

Albite is a hard (Mohs 6-6.5) feldspar, typically white to colorless with a vitreous to pearly luster and a white streak. The most diagnostic feature is fine parallel striations (albite twinning lamellae) visible on the best cleavage surface, which distinguish plagioclase from the potassium feldspars.

It has two good cleavage directions meeting at close to 90 degrees. The cleavelandite variety appears as fan-like aggregates of thin curved blades.

Distinguish albite from orthoclase and microcline by the twinning striations (absent in K-feldspar). Separating albite from other plagioclase members like oligoclase usually requires optical or chemical analysis, since they differ mainly in calcium content.

Albite is used industrially as a soda feldspar in the ceramics and glass industries, where it serves as a flux and source of sodium and alumina for glazes, porcelain, and glass batches.

Gemmy and iridescent varieties have ornamental value: peristerite is cut as a moonstone-type gem for its bluish schiller, and well-crystallized cleavelandite and albite specimens are collected. Albite-rich pegmatites are also important hosts for gem tourmaline, beryl, and lithium minerals, making the mineral significant to gem mining.

Metaphysically albite is sometimes associated with mental clarity and calm, though such uses are traditional beliefs rather than proven properties.