Perovskite

**Perovskite**
Perovskite
General
Category	Oxide minerals
Formula; (repeating unit)	CaTiO3
Strunz classification	04.CC.30
Crystal system	Orthorhombic (2/m 2/m 2/m) space group: Pnma
Identification
Formula mass	135.96
Color	Black, reddish brown, pale yellow, yellowish orange
Crystal habit	Pseudo cubic – crystals show a cubic outline
Twinning	complex penetration twins
Cleavage	[100] good, [010] good, [001] good
Fracture	Conchoidal
Mohs scale hardness	5–5.5
Luster	Adamantine to metallic; may be dull
Streak	grayish white
Diaphaneity	Transparent to opaque
Specific gravity	3.98–4.26
Optical properties	Biaxial (+)
Refractive index	nα=2.3, nβ=2.34, nγ=2.38
Other characteristics	non-radioactive, non-magnetic
References

This article is about the mineral, for the crystal structure see perovskite structure

Perovskite (Pv) is a calcium titanium oxide mineral species composed of calcium titanate, with the chemical formula Ca Ti O₃.

The mineral was discovered in the Ural Mountains of Russia by Gustav Rose in 1839 and is named after Russian mineralogist Lev Perovski (1792–1856).^[1]

It lends its name to the class of compounds which have the same type of crystal structure as CaTiO₃ (^XIIA²⁺^VIIB⁴⁺X^2–₃) known as the perovskite structure.^[6] The perovskite crystal structure was published in 1945 from X-ray diffraction data on barium titanate by the Irish crystallographer Helen Dick Megaw (1907–2002).^[7]

Occurrence

Perovskite is found in contact carbonate skarns at Magnet Cove, Arkansas. It occurs in altered blocks of limestone ejected from Mount Vesuvius. It occurs in chlorite and talc schist in the Urals and Switzerland.^[8] It is also found as an accessory mineral in alkaline and mafic igneous rocks, nepheline syenite, melilitite, kimberlites and rare carbonatites. Perovskite is a common mineral in the Ca-Al-rich inclusions found in some chondritic meteorites.^[2]

A rare earth-bearing variety, knopite, (Ca,Ce,Na)(Ti,Fe)O₃) is found in alkali intrusive rocks in the Kola Peninsula and near Alnö, Sweden. A niobium-bearing variety, dysanalyte, occurs in carbonatite near Schelingen, Kaiserstuhl, Germany.^[8]^[9]^[10]^[11]

Structure

The mineral CaTiO3 was assigned a cubic structure. With more modern techniques of structural characterization, it’s easy to know now that the structure of CaTiO3 is somewhat distorted from the ideal perovskite structure. The molecular structure states that it has 29.48 % of Ca, Ti 35.22% and 35.30% of O.^[1]^[3]

Special Characteristics

The stability of perovskite in igneous rocks is limited by its reaction relation with sphene. In volcanic rocks perovksite and sphene are not found together, the only exception being in an atindite from Cameroun^[4]

Physical Properties

The sub-metallic- metallic luster, colorless streak cube like structure along with imperfect cleavage brittle tenacity makes the physical property of perovskite. It covers a wide range of colors from black, brown, gray,orange to yellow. Crystals of perovskite appear as cubes, but this is deceiving. Perovskite is actually pseudocubic and really orthorhombic in symmetry. Having almost the same look as Galena can fool sometime. But Galena has a better metallic luster, greater density and perfect cleavage (Luxová, 2008). Physical properties of interest among perovskites include superconductivity, colossal magnetoresistance, ionic conductivity, and a multitude of dielectric properties, which are of great importance in microelectronics and telecommunication. Because of the great flexibility inherent in the perovskite structure there are many different types of distortions which can occur from the ideal structure. These include tilting of the octahedra, displacements of the cations out of the centers of their coordination polyhedra, and distortions of the octahedra driven by electronic factors “Jahn-Teller distortions”.^[5]

Geologic Occurrence

Basically found in the earth’s mantle, the perovskite’s occurrence at Khibina is restricted to the under saturated ultra-mafic rocks and foidolites, due to the unstability in a paragenesis with feldspars. The complexity is made by an extended series of rocks from early alkaline ultramafic members to late carbonatites that comprise alkaline and mafic igneous rocks such as nepheline syenite, melilitite, kimberlites and rare carbonatites in ultramafites. Pervoskite occurs as small anhedral to subhedral crystals filling interstices between the rock forming silicates. The Olivinites and pyroxenites are enriched in perovskite with chemical compositions in some ultramafic-alkaline intrusive complexes that are close to pure calcium titanate (Chakhmouradian, 1990).

Who in the World

The Perovskite structure was named to give an honor of Lev Alexeivitch Perovsky, and it might be thought that he was its discoverer. In actuality it was discovered and named in 1839 by a German chemist and mineralogist, Gustav Rose. Perovsky, a son of Ukrainian nobleman, had a lengthy military career. He was also the Secretary of the Interior and later Director of the Imperial Cabinet. He apparently also had an interest in mineralogy that was sufficiently well-known to be honored by Rose in the naming of the new mineral (Lemanov, 1999).

References

^ ^a ^b ^c Perovskite. Webmineral
^ ^a ^b Perovskite. Handbook of Mineralogy
^ ^a ^b Physical Property of Perovskite.Inoue
^ ^a ^b Science Direct. Veksler
^ ^a ^b Strucutral Science Online Lufaso
^ Wenk, Hans-Rudolf; Bulakh, Andrei (2004). Minerals: Their Constitution and Origin. New York, NY: Cambridge University Press. p. 413. ISBN 978-0521529587.
^ Megaw, Helen (1945). "Crystal Structure of Barium Titanate". Nature. 155 (3938): 484. doi:10.1038/155484b0.
^ ^a ^b Palache, Charles, Harry Berman and Clifford Frondel, 1944, Dana's System of Mineralogy Vol. 1, Wiley, 7th ed. p. 733
^ Deer, Howie and Zussman, An Introduction to the Rock Forming Minerals Longman 1966, ISBN 0582442109
^ Knopite. Mindat
^ Dysanalyte. Mindat