Nambulite: Gemstone Information
Nambulite is (Li,Na)Mn2 4Si5O14(OH) and occurs as triclinic prismatic to tabular transparent reddish brown crystals with an orange tint and a perfect cleavage in one direction. The hardness is 6.5 and SG 3.51–3.55. The RI for the alpha, beta and gamma rays is 1.707, 1.710 and 1.730, biaxial positive with birefringence 0.023. Nambulite occurs in veinlets cutting manganese oxide ores. Rare fashioned specimens may have come from the Funakozawa and Ohtaniyama mines, Ohno,Iwate Prefecture, Japan.