Musgravite

Musgravite or magnesiotaaffeite-6N’3S is a rare oxide mineral used as a gemstone. Its type locality is the Ernabella Mission, Musgrave Ranges, South Australia, for which it was named following its discovery in 1967. It is a member of the taaffeite family of minerals, and its chemical formula is Be(Mg, Fe, Zn)2Al6O12. Its hardness is 8 to 8.5 on the Mohs scale. Due to its rarity, the mineral can sell for roughly USD$35,000 per carat.

Musgravite

General

Category Oxide minerals

Formula (Mg,Fe,Zn)2BeAl6O12

Strunz classification 04.FC.25

Crystal system Trigonal

Identification

Color Grey green to green

Fracture Conchoidal

Mohs scale hardness 8–8.5

Luster Vitreous

Diaphaneity Transparent

Specific gravity 3.62–3.68

Optical properties Uniaxial

Refractive index nω = 1.739, nε = 1.735

Birefringence δ = 0.014 to 0.016

Features

Magnesiotaaffeite- 6N'3S is an oxide with the chemical formula Mg₂BeAl₆O₁₂. It crystallizes in the trigonal system. It is a brittle, transparent to semi-transparent mineral. It has a glassy luster. Its hardness on the Mohs scale is between 8 and 8.5.

Classification

According to the Nickel-Strunz classification, magnesiotaaffeite-6N'3S belongs to "04.FC: Hydroxides (without V or U), with OH, without H₂O; octahedra showing angles" together with the following minerals: bernalite, dzhalindite, söhngeïte, burtite, mushistonite, natanite, schoenfliesite, vismirnovite, wickmanite, jeanbandyite, mopungite, stottite, tetrawickmanite, ferronigerite-2N1S, magnesionigerite-6N6S, magnesionigerite-2N1S, ferronigerite-6N6S, zinconigerite-2N1S, zinconigerite-6N6S and magnesioaffeite-2N'2S.

Formation and deposits

It was discovered at the Ernabella Mission, in the Musgrave Range (South Australia, Australia), where it is usually found associated with phlogopite, sapphire and spinel. It has also been described in Madagascar, Tanzania, France, Austria, Greenland and Antarctica.

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