Chemistry:Eucryptite

From HandWiki
Eucryptite
Eucryptite-202043.jpg
Eucryptite grains in albite from the type locality (size: 9.3 × 7.0 × 2.8 cm)
General
CategorySilicate mineral
Formula
(repeating unit)
LiAlSiO4
Crystal systemTrigonal
Crystal classRhombohedral (3)
H-M symbol: (3)
Space groupR3
Unit cella = 13.48, c = 9.01 [Å]; Z = 18
Identification
ColorBrown, colorless, white
Crystal habitRare as euhedral crystals, coarse crystalline aggregates and massive
CleavageIndistinct on {1010} and {0001}
FractureConchoidal
TenacityVery brittle
Mohs scale hardness6.5
|re|er}}Vitreous
StreakWhite
DiaphaneityTransparent to translucent
Density2.67
Optical propertiesUniaxial (+)
Refractive indexnω = 1.570 – 1.573 nε = 1.583 – 1.587
Birefringenceδ = 0.013
Other characteristicsFluoresces pink to red or orange under SW UV
References[1][2][3]

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.[2]

It occurs as a secondary alteration product of spodumene. It was first described in 1880 for an occurrence at its type locality, Branchville, Connecticut.[1] Its name was from the Greek for well concealed, for its typical occurrence embedded in albite.[1][2]

References

  1. 1.0 1.1 1.2 Mindat.org
  2. 2.0 2.1 2.2 Handbook of Mineralogy
  3. Webmineral data
  4. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode2021MinM...85..291W.