Milarite: Gemstone Information

Milarite is KCa2AlBe2Si12O3005H2O and a member of the osumilite group in which it forms transparent to translucent colourless to pale yellow or green prismatic crystals, typically well formed, of the hexagonal system. The hardness is 5.5–6 and the SG 2.46–2.61. The RI for the ordinary and extraordinary rays is 1.532–1.551 and 1.529–1.548, uniaxial negative with birefringence 0.003. Milarite is found in vugs in granites and syenites or in hydrothermal veins. Large crystals are found in the Jose Pinto pegmatite, Jaguarcu, Coronel Fabriciano, Minas Gerais, Brazil and smaller examples at several Swiss localities though not in the Val Milar after which it was named! A sapphire-blue scandium-bearing variety with RI 1.549 and 1.560, birefringence 0.011 with pleochroism strong blue to green has been reported from Tamil Nadu, India. The Sc content was 1.9%. The Mineralogical Record 35(5) carries a useful paper showing Alpine milarite crystals up to 1 cm.