Perovskite

Perovskite, or PEROFSKITE, a mineral consisting of calcium titanate, CaTiO 31 usually with a small proportion of the calcium replaced by iron. The crystals found in schistose rocks have the form of cubes, which are sometimes modified on the edges and corners by numerous small planes; on the other hand, the crystals occurring as an accessory constituent of eruptive rocks are octahedral in form and microscopic in size. Although geometrically cubic, the crystals are always doubly refracting, and they sometimes show evidence of complex mimetic twinning; their structure as shown in polarized light is very similar to that of the mineral boracite, and they are therefore described as pseudo-cubic. There are distinct cleavages parallel to the faces of the cube. The colour varies from pale yellow to blackishbrown and the lustre is adamantine to metallic; the crystals are transparent to opaque. The index of refraction is high, the hardness 52 and the specific gravity 4.0. The mineral was discovered at Achmatovsk near Zlatonst in the Urals by G. Rose in 1839, and named in honour of Count L. A. Perovsky; at this locality large cubes occur with calcite and magnetite in a chlorite-schist. Similar crystals are also found in talc-schist at Zermatt in Switzerland. The microscopic octahedral crystals are characteristic of melilite basalt and nepheline basalt; they have also been found in peridotite and serpentine. (L. J. S.)