Stichtite

Stichtite
	240px Stichtite on serpentine, Dundas, Tasmania
General
Category	Carbonate minerals
Formula; (repeating unit)	Mg6Cr2CO3(OH)16·4H2O
Strunz classification	05.DA.50
Crystal symmetry	Trigonal - hexagonal scalenohedral; H-M symbol: (32/m); Space group: R 3m
Unit cell	a = 6.19 Å, c = 46.47 Å; Z=3
Identification
Colour	Lilac to rose-pink
Crystal habit	Fibrous to platy aggregates
Crystal system	Trigonal
Cleavage	Perfect on {0001}
Tenacity	ﬂexible, not elastic
Mohs scale hardness	1.5 - 2
Luster	Waxy to resinous
Streak	Very pale lilac to white
Diaphaneity	Transparent
Specific gravity	2.16
Optical properties	Uniaxial (+)
Refractive index	nω = 1.516 nε = 1.542
Birefringence	δ = 0.026
Pleochroism	Weak; O = dark rose-pink to lilac E = light rose-pink to lilac
References

Stichtite is a mineral, a carbonate of chromium and magnesium; formula Mg₆Cr₂C O₃(OH)₁₆·4H₂O. Its colour ranges from pink through lilac to a rich purple colour. It is formed as an alteration product of chromite containing serpentine. It occurs in association with barbertonite (the hexagonal polymorph of Mg₆Cr₂CO₃(OH)₁₆·4H₂O), chromite and antigorite.^[1]

Discovered in 1910 on the west coast of Tasmania, Australia, it was first recognised by A.S. Wesley a former chief chemist with the Mount Lyell Mining and Railway Company, it was named after Robert Carl Sticht the manager of the mine.^[4]

It is observed in combination with green serpentine at Stichtite Hill near the Dundas Extended Mine, Dundas - east of Zeehan, as well as on the southern shore of Macquarie Harbour. It is exhibited in the West Coast Pioneers Museum in Zeehan. The only commercial mine for stichtite serpentine is located on Stichtite Hill^{[citation needed]}. Stichtite has also been reported from the Barberton District, Transvaal; Darwendale, Zimbabwe; near Bou Azzer, Morocco; Cunningsburgh, the Shetland Islands of Scotland; Langban, Varmland, Sweden; the Altai Mountains, Russia; Langmuir Township, Ontario and the Megantic, Quebec; Bahia, Brazil; and the Keonjhar district, Orissa, India.^[1]

Stichtite on serpentine Basic hydrous magnesium chromate and carbonate New Amianthus Mine Transvaal South Africa 1623.jpg

Stichtite on serpentine, New Amianthus Mine, Transvaal South Africa

References

↑ ^1.0 ^1.1 ^1.2 Stichtite data in the Handbook of Mineralogy
↑ Stichtite on Mindat.org
↑ Stichtite data on Webmineral.com
↑ Tasmania Department of Mines, Geological Survey Record Number 9 Catalogue of the Minerals of Tasmania. Revised edition 1970, page 96