Euclase Locality: Lost Hope Mine, Mwami, Karoi (Urungwe; Hurungwe) District, Mashonaland West, Zimbabwe (Locality at mindat.org) Size: miniature, 4.2 x 3.3 x 1. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Euclase
A beryllium-aluminium silicate-hydroxide whose perfect cleavage gives it the name 'good fracture' — occasionally a pale-blue gem.
Intro adapted from Wikipedia (CC BY-SA).
Euclase is an IMA-recognized mineral species in the silicate class, with the chemical formula BeAlSiO₄(OH).
It crystallizes in the monoclinic crystal system (space group P2_1/a).
Key properties: Mohs hardness 7.5; specific gravity 2.99–3.1; typically blue or colorless or green; White streak; Vitreous, somewhat pearly on cleavages luster; refractive index 1.659; optically biaxial.
IMA symbol Ecs, grandfathered status — known before the IMA’s founding, named in 1792.
The product of decomposition of beryl in pegmatites, and in low-temperature alpine veins.
It is found associated with Feldspar, quartz, topaz, beryl, mica, calcite, ankerite, chlorite.
Its name comes from the Greek for easily and fracture regarding its perfect cleavage.
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