Sugilite

Sugilite
16kg Manganoan Sugilite, GIA Laboratory Certified, Smithsonian Exhibition Stone, I.Kurgan Royal Azel, Hall of Gems Smithsonian Museum 1981, 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
Crystal class	Dihexagonal dipyramidal (6/mmm) H-M symbol: (6/m 2/m 2/m)
Space group	P6/mcc
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
Cleavage	Poor on {0001}
Mohs scale hardness	6–6+1⁄2
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

Sugilite (/ˈsuːɡɪlaɪt/ SOO-gi-lyt) 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".

The mineral is also referred to as lavulite, luvulite, and royal azel by gem and mineral collectors.

Sugilite on Matrix, 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