eucryptite

{{Infobox mineral | name = Eucryptite | category = Silicate mineral | image = Eucryptite-202043.jpg | imagesize = | caption = Eucryptite grains in albite from the type locality (size: 9.3 × 7.0 × 2.8 cm) | formula = LiAlSiO4 | IMAsymbol = Ecp | system = Trigonal | class = Rhombohedral () H-M symbol: () | symmetry = R | unit cell = a = 13.48, c = 9.01 [Å]; Z = 18 | color = Brown, colorless, white | habit = Rare as euhedral crystals, coarse crystalline aggregates and massive | cleavage = Indistinct on {100} and {0001} | fracture = Conchoidal | tenacity = Very brittle | mohs = 6.5 | luster = Vitreous | refractive = nω = 1.570 – 1.573 nε = 1.583 – 1.587 | opticalprop = Uniaxial (+) | birefringence = δ = 0.013 | streak = White | density = 2.67 | diaphaneity = Transparent to translucent | other = Fluoresces pink to red or orange under SW UV | references = }}

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.