Hauyne: Gemstone Information
Haüyne is (Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1–2 and forms very bright and attractive though uncommon transparent blue dodecahedral or pseudo octahedral crystals of the cubic system. It is also an important constituent of lapis-lazuli. The hardness is 5.5–6 and the SG 2.40–2.50. The RI is usually near 1.502 for the material from the Eifel. Some of this material has been reported to show an orange-red fluorescence under LWUV. Haüyne occurs in alkaline nepheline or leucite-rich igneous rocks; fine bright blue crystals from Mendig and Mayen in the Eifel region of western Germany.