Dickinsonite: Gemstones Information
Dickinsonite is KNa4Ca(Mn2,Fe2)14Al(PO4)12(OH)2 and forms very small monoclinic commonly rhombohedral olive green tabular transparent to translucent crystals with a perfect cleavage in one direction with striations giving a triangular pattern. The hardness is 3.5–4 and the SG 3.34–3.41. The RI for the alpha, beta and gamma rays is 1.648–1.658,1.655–1.662, 1.662–1.671, biaxial positive with birefringence 0.013.Dickinsonite, of which some faceted stones turn up occasionally, occurs as a high-temperature mineral in granite pegmatites. Crystals are from Branchville, Connecticut, USA.