Ludlamite: Gemstone Information
Ludlamite is (Fe2,Mg,Mn2)3(PO4)24H2O and forms apple- to bright green prismatic crystals in the monoclinic system with one direction of perfect cleavage and a hardness of 3.5. The SG is 3.12–3.19. The RI for the alpha, beta and gamma rays is 1.650–1.653, 1.669–1.675, and 1.688–1.697,biaxial positive with birefringence 0.038–0.044. Ludlamite occurs in granite pegmatites, resulting from the alteration of primary phosphates.Specimen material in fine crystals comes from the Blackbird mine, Lemhi County, Idaho, USA.