Sugilite

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Sugilite
Sugilite-162617.jpg
Sugilite from Wessels Mine in Northern Cape Province, South Africa
General
Category Cyclosilicate
Formula
(repeating unit)
KNa2(Fe,Mn,Al)2Li3Si12O30
Strunz classification 09.CM.05
Dana classification 63.02.01a.09
Crystal symmetry Hexagonal dihexagonal dipyramidal
H-M symbol: (6/m 2/m 2/m)
Space group: P 6/mcc
Unit cell a = 10 Å, c = 14 Å; Z=2
Identification
Color Light brownish-yellow, purple, violet, reddish violet, pale pink, colorless
Crystal habit Prismatic crystals, typically granular to massive
Crystal system Hexagonal
Cleavage Poor on {0001}
Mohs scale hardness 6–6½
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.74
Optical properties Uniaxial (-)
Refractive index nω = 1.610 nε = 1.607
Birefringence δ = 0.003
Pleochroism Weak
References [1][2][3]

Sugilite (/ˈsɡɨlt/ SOO-gi-lyt), also known as lavulite, is a relatively rare pink to purple cyclosilicate mineral with the complex chemical formula KNa2(Fe,Mn,Al)2Li3Si12O30. Sugilite crystallizes in the hexagonal system with prismatic crystals. The crystals are rarely found and the form is usually massive. It has a Mohs hardness of 5.5 to 6.5 and a specific gravity of 2.75 to 2.80. It is mostly translucent.

Sugilite was first described in 1944 by the Japanese petrologist Ken-ichi Sugi (1901–1948) for an occurrence on Iwagi Islet, Japan, where it is found in an aegirine syenite intrusive stock. It is found in a similar environment at Mont Saint-Hilaire, Quebec, Canada. In the Wessels mine in Northern Cape Province of South Africa, sugilite is mined from a strata-bound manganese deposit. It is also reported from Liguria and Tuscany, Italy; New South Wales, Australia and Madhya Pradesh, India.

Note: The mineral is commonly pronounced with a soft "g", as in "ginger". However, as with most minerals, its pronunciation is intended to be the same as the person it is named after; in this case, the Japanese name Sugi has a hard "g", as in "geese".

Purple sugilite on a matrix of baryte crystals, Wessels Mine in Northern Cape Province, South Africa, size: 2.4 x 2.1 x 1.2 cm

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