Minerals in space group 28

Prehnite is an inosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2 with limited Fe3+ substitutes for aluminium in the structure. Prehnite crystallizes in the orthorhombic crystal system, and most often forms as stalactitic, botryoidal, reniform or globular aggregates, with only just the crests of small crystals showing any faces, which are almost always curved or composite. Very rarely will it form distinct, well-individualized crystals showing a square-like cross-section, including those found at the Jeffrey Mine in Asbestos, Quebec, Canada. Prehnite is brittle with an

Krennerite is an orthorhombic gold telluride mineral which can contain variable amounts of silver in the structure. The formula is AuTe2, but specimen with gold substituted by up to 24% with silver have been found ([Au0.77Ag0.24]Te2). Both of the chemically similar gold-silver tellurides, calaverite and sylvanite, are in the monoclinic crystal system, whereas krennerite is orthorhombic.

Kostovite (IMA symbol: Ktv) is a rare orthorhombic-pyramidal gray white telluride mineral containing copper and gold with chemical formula AuCuTe4. == Discovery and occurrence== It was discovered by Bulgarian mineralogist Georgi Ivanov Terziev, who named it in honor of his professor Ivan Kostov (Иван Костов) (1913–2004). In 1965 kostovite was approved as a new species by the International Mineralogical Association. The type locality is Chelopech copper ore deposit, Bulgaria. Small deposits have also been found in Kochbulak (Eastern Uzbekistan), Commoner mine (Zimbabwe), Kamchatka (Russian Far