Painite

Painite
Painite from Myanmar, 2 cm long
General
Category	Borates
Formula (repeating unit)	CaZrAl9O15(BO3)
Strunz classification	06.AB.85
Dana classification	7.5.2.1
Crystal system	Hexagonal 6/m,[1] although earlier reported as hexagonal 6[2]
Unit cell	a = 8.72 Å, c = 8.46 Å; Z = 2
Identification
Color	Red, brownish, orange-red
Crystal habit	Elongated crystals, pseudo-orthorhombic[3][2]
Crystal symmetry	Hexagonal 6/m
Mohs scale hardness	8
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	4.01
Optical properties	Uniaxial (-)
Refractive index	no = 1.8159, ne = 1.7875[3]
Pleochroism	Ruby-red parallel to [0001]; pale brownish orange or pale red-orange at right angles to [0001]
Solubility	Insoluble in acids[3]
Other characteristics	Not radioactive
References	[2][4][5]

Painite is a very rare borate mineral. It was first found in Myanmar by British mineralogist and gem dealer Arthur C.D. Pain in the 1950s. When it was confirmed as a new mineral species, the mineral was named after him.^[2]

The chemical makeup of painite contains calcium, zirconium, boron, aluminium and oxygen (CaZrAl₉O₁₅(BO₃)). The mineral also contains trace amounts of chromium and vanadium. Painite has an orange-red to brownish-red color similar to topaz due to trace amounts of iron. The crystals are naturally hexagonal in shape, and, until late 2004, only two had been cut into faceted gemstones.^[6]

Discovery and occurrence

Striated, euhedral painite crystal (size: 0.9×0.8×0.7 cm

For many years, only three small painite crystals were known to exist. Before 2005 there were fewer than 25 known crystals found, though more material has been unearthed recently in Myanmar.

More recently, painite specimens have been discovered at a new location in northern Myanmar. It is believed that further excavations in this area will yield more painite crystals.

Extensive exploration in the Mogok region has identified several new painite occurrences that have been vigorously explored resulting in several thousand new painite specimens.^[7] Most of the recent crystals and fragments are dark, opaque, incomplete crystals. A modest number of transparent crystals have been found and have been either saved as crystals or cut into gemstones.

Faceted painite with color change from brown to red, 0.86 ct, from the Thurein Taung Mine, Mogok, Myanmar (Burma)

Originally few of the known painite specimens were privately owned. The rest of the stones were distributed between the British Museum of Natural History, Gemological Institute of America, California Institute of Technology and the GRS Gem Research Laboratory in Lucerne, Switzerland.

References

1. T Armbruster, N Dobelin, A Peretti, D Gunther, E Reusser, B Grobety (2004). "The crystal structure of painite CaZrB(Al9O18) revisited" (PDF). American Mineralogist 89: 610–613.
2. Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C., ed. (2003). "Paynite". Handbook of Mineralogy (PDF). V (Borates, Carbonates, Sulfates). Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209740. Retrieved December 5, 2011.
3. Claringbull GF, Hey MH, Payne CJ (1957). "Painite, a New Mineral from Mogok, Burma". Mineralogical Magazine 31 (236): 420–5. doi:10.1180/minmag.1957.031.236.11.
4. Painite. Webmineral. Retrieved on 2012-05-28.
5. Painite. Mindat.org. Retrieved on 2012-05-28.
6. Ten gemstones that are rarer than diamond. io9.com
7. Painite history at Caltech. Minerals.gps.caltech.edu. Retrieved on 2012-05-28.

Corundum var. ruby on large painite crystal, Mogok, Burma. Size: 3.7×3.1×2.3 cm.