Richterite: Gemstone Information
Richterite is Na(NaCa)Mg5Si8O22(OH)2 and a member of the amphibole group. It forms flattened prismatic monoclinic crystals with one direction of perfect cleavage, hardness 5–6 and SG 2.97–3.45. Opaque blue material has been fashioned. The RI for the alpha, beta and gamma rays is 1.605–1.624, 1.618–1.64 and 1.627–1.641, biaxial negative. Richterite occurs in contact-metamorphosed limestones and in alkalic igneous rocks and carbonatites. The blue material has been found at the Kalahari manganese orefield, South Africa.