Euclase: Gemstone Information
Euclase is BeAlSiO4 (OH) and forms flattened transparent prismatic monoclinic crystals with some morphological complexity and one direction of perfect cleavage. The colour is most commonly a pale aquamarine or green but crystals of a very fine dark blue (from iron) have been found at the Miami mine in Zimbabwe and a number of faceted specimens exist,despite the pronounced cleavage. The hardness is 7.5 and the SG usually near 3.10. The RI for the alpha, beta and gamma rays is 1.651–1.653,1.655–1.657 and 1.669–1.675 with a birefringence of 0.020, biaxial positive.In the deeper-coloured stones, two vague absorption bands at 468 and 455 nm may be seen as well as a strong doublet at 705 nm in the red, due to chromium which is sometimes present. Euclase is found in pegmatites and is formed from the decomposition of beryl. Apart from the Zimbabwe deposit gem euclase usually comes from Minas Gerais, Brazil.