Sugilite

Sugilite
Sugilite from Wessels Mine in Northern Cape Province, South Africa
General
Category	Cyclosilicate
Formula (repeating unit)	KNa2(Fe,Mn,Al)2Li3Si12O30
Strunz classification	9.CM.05
Dana classification	63.02.01a.09
Crystal system	Hexagonal
Unit cell	a = 10, 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 symmetry	Hexagonal - dihexagonal dipyramidal H-M symbol: (6/m 2/m 2/m) Space group: P 6/mcc
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 (/ˈsuːɡᵻlaɪt/ 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".^[4]

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

See also

• List of minerals
• List of minerals named after people

References

1. Sugilite data on Webmineral
2. Sugilite on Mindat.org
3. Sugilite in the Handbook of Mineralogy
4. "OpenLearn Live: 8th September 2015 - Meet The Minerals". OpenLearn. The Open University. Retrieved 20 January 2016.

External links

• R. V. Dietrich