Serendibite: Gemstones Information
Serendibite is Ca2(Mg,Al)6(Si,Al,B)6O20 and forms small greyish bluegreen to deep blue transparent tabular crystals of the triclinic system with hardness 6.5–7 and SG 3.43–3.44. The RI for the alpha, beta and gamma rays is 1.700–1.738, 1.703–1.741 and 1.706–1.743, biaxial negative with birefringence 0.005. Strong pleochroic colours are yellowish green,bluish green and violet-blue. Serendibite from Gangapitiya, Ambakotte,Sri Lanka, has presumably been found as alluvial material though the mineral, a member of the aenigmatite group, occurs generally in skarns affected by boron metasomatism.