Crystal Sugilite

Category

Cyclosilicate

Formula
(repeating unit)

KNa₂(Fe,Mn,Al)₂Li₃Si₁₂O₃₀

Strunz classification

9.CM.05

Dana classification

63.02.01a.09

Crystal system

Hexagonal
Dihexagonal dipyramidal class

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
H-M symbol: (6/m 2/m 2/m)
Space group: P 6/mcc

Cleavage

Poor on {0001}

Mohs scalehardness

6–6½

Luster

Vitreous

Streak

White

Diaphaneity

Transparent to translucent

Specific gravity

2.74

Optical properties

Uniaxial (-)

Refractive index

n_ω = 1.610 n_ε = 1.607

Birefringence

δ = 0.003

Pleochroism

Weak

References

^[1][2][3]