FREIESLEBENITE  , a rare

mineral consisting of sulphantimonite of silver and lead, (Pb,Ag2)5Sb4S11• The monoclinic crystals are prismatic in habit, with deeply striated prism and dome faces . The colour is steel-grey, and the lustre metallic; hardness 22i specific gravity 6.2 . It occurs with argentite, chalybite and galena in the silver veins of the Himmelsfurst mine at Freiberg, Saxony, where it has been known since 1720 . The species was named after J . K . Freiesleben, who had earlier called it Schilf-Glaserz . Other localities are Hiendelaencina near Guadalajara in Spain, Kapnik-Banya in Hungary, and Guanajuato in Mexico . A species separated from freieslebenite by V. von Zepharovich in 1871, because of differences in crystal-line form, is known as diaphorite (from &mope, " difference") ; it is very similar to freieslebenite in appearance and has perhaps the same chemical composition (or possibly Ag2PbSb2S5), but is orthorhombic in crystallization . A third mineral also very similar to freieslebenite in appearance is the orthorhombic andorite, AgPbSbaS6, which is mined as a silver ore at Oruro in ' Bolivia .