Eucryptite (Size: 25mm x 20mm x 10mm) Locality: Haapaluoma pegmatite, Peräseinäjoki, Seinäjoki, Western and Inner Finland Region, Finland Eucryptite, really dif — Photo: Jyrki Autio · Public domain
Eucryptite
A lithium aluminosilicate that sometimes pseudomorphically replaces spodumene in lithium pegmatites.
Intro adapted from Wikipedia (CC BY-SA).
Eucryptite is an IMA-recognized mineral species in the silicate class, with the chemical formula LiAlSiO₄.
It crystallizes in the hexagonal crystal system (space group R-3). It is a member of the Phenakite structural group.
Key properties: Mohs hardness 6.5; specific gravity 2.66–2.67; typically colorless or white or brown; white streak; vitreous luster; refractive index 1.578; optically uniaxial.
IMA symbol Ecp, grandfathered status — known before the IMA’s founding, named in 1880.
Found in lithium-rich pegmatites.
It is found associated with Albite, spodumene, petalite, amblygonite, lepidolite, quartz.
Its name comes from the Greek for well and concealed, in reference to its occurrence as intimate intergrowths with albite.
Collections: Collector Favorites, Rare & Remarkable.