Friedelite: Gemstone Information Friedelite is Mn2 8 Si6O15(OH,Cl)10 and fashioned specimens are transpar-ent to translucent rose-red to orange with hardness of 4–5, SG 3.04–3.06. RI for the ordinary and extraordinary rays is 1.654–1.656 and 1.620–1.625 with a birefringence of 0.030, uniaxial negative. The crystal system is monoclinic, crystals occurring most commonly as pseudohexagonal tablets. Absorption bands may be seen centred at 556 nm and near 456 nm and some specimens have shown reddish fluorescence; other effects have been reported, including yellow (LWUV) and green (SW). Most ornamental specimens of friedelite have come from Franklin, New Jersey, USA,where they occur in metamorphosed manganese–iron deposits.