Brucite

Brucite is a magnesium hydroxide mineral, Mg(OH)₂, and the namesake of the brucite group, which also includes pyrochroite and portlandite. It crystallizes in the hexagonal system, typically forming tabular to platy crystals with a pearly, waxy luster on the basal cleavage, a hardness of only 2.5–3, and a sectile, foliated habit reminiscent of mica or gypsum. Colors range from colorless and white to pale green, blue, yellow, and brown, depending on trace iron or manganese substitution; a fibrous, asbestos-like variety known as nemalite is also recognized. Brucite forms in low-temperature metamorphic environments, chiefly in serpentinized dolomites, altered peridotites, and chlorite-talc schists, commonly alongside calcite, serpentine, chrysotile, magnesite, and hydromagnesite.

The species was named in 1824 after American mineralogist Archibald Bruce, and its type locality is Castle Point, Hoboken, in Hudson County, New Jersey, where it was first found in serpentinite. The most celebrated classic source, however, is the Wood's Chrome Mine at Texas, Lancaster County, Pennsylvania, which produced some of the largest and finest brucite crystals ever found — golden, translucent plates historically traded under the local name "texalite" — with additional fine material from the nearby Cedar Hill Quarry. Other important North American localities include the Sierra Magnesite Mine at Gabbs, Nevada, the Tilly Foster Mine in Brewster, New York, Crestmore Quarry in California, and the Maxwell Quarry at Wakefield, Quebec, while the Asbestos (Val-des-Sources) district in Quebec has yielded long fibrous nemalite masses and cuttable pale blue material.

Exceptional specimens continue to emerge from the Killa Saifullah District in Balochistan, Pakistan, now among the world's finest modern sources of large, gemmy, transparent brucite plates, alongside notable finds from N'Chwaning II Mine in South Africa's Kalahari Manganese Field, where brucite is prized in combination with calcite, and from Tsumeb, Namibia, known for delicate pale green crystals. Italian collectors also recognize occurrences such as the Val di Serra Quarry near Ala in Trentino-Alto Adige. Because well-formed, transparent brucite crystals are genuinely uncommon compared to its massive and fibrous forms, sharp, lustrous plates from these historic and modern localities remain highly sought after by systematic mineral collectors and serve as a minor ore of magnesium and industrial source of magnesia.