Eucryptite grains in albite from the type locality (size: 9.3 × 7.0 × 2.8 cm)
General
Category
Silicate mineral
Formula (repeating unit)
LiAlSiO4
IMA symbol
Ecp[1]
Crystal system
Trigonal
Crystal class
Rhombohedral (3) H-M symbol: (3)
Space group
R3
Unit cell
a = 13.48, c = 9.01 [Å]; Z = 18
Identification
Color
Brown, colorless, white
Crystal habit
Rare as euhedral crystals, coarse crystalline aggregates and massive
Cleavage
Indistinct on {1010} and {0001}
Fracture
Conchoidal
Tenacity
Very brittle
Mohs scale hardness
6.5
Luster
Vitreous
Streak
White
Diaphaneity
Transparent to translucent
Density
2.67
Optical properties
Uniaxial (+)
Refractive index
nω = 1.570 – 1.573 nε = 1.583 – 1.587
Birefringence
δ = 0.013
Other characteristics
Fluoresces pink to red or orange under SW UV
References
[2][3][4]
Eucryptite is a lithium bearing aluminium silicate mineral with formula LiAlSiO4. It crystallizes in the trigonal – rhombohedral crystal system. It typically occurs as granular to massive in form and may pseudomorphically replace spodumene. It has a brittle to conchoidal fracture and indistinct cleavage. It is transparent to translucent and varies from colorless to white to brown. It has a Mohs hardness of 6.5 and a specific gravity of 2.67. Optically it is uniaxial positive with refractive index values of nω = 1.570 – 1.573 and nε = 1.583 – 1.587.
Its typical occurrence is in lithium-rich pegmatites in association with albite, spodumene, petalite, amblygonite, lepidolite and quartz.[3]
It occurs as a secondary alteration product of spodumene. It was first described in 1880 for an occurrence at its type locality, Branchville, Connecticut.[2] Its name was from the Greek for well concealed, for its typical occurrence embedded in albite.[2][3]
Eucryptite is a lithium bearing aluminium silicate mineral with formula LiAlSiO4. It crystallizes in the trigonal – rhombohedral crystal system. It typically...
pegmatites and aplites. Associated minerals include: quartz, albite, petalite, eucryptite, lepidolite and beryl. Transparent material has long been used as a gemstone...
petalite, amblygonite, lepidolite, elbaite, cassiterite, columbite, apatite, eucryptite, muscovite, albite and microcline. About 82% of the world's known reserves...