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 212, specific gravity 6.2. It occurs with argentite, chalybite and galena in the silver veins of the Himmelsfürst 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-Bánya in Hungary, and Guanajuato in Mexico. A species separated from freieslebenite by V. von Zepharovich in 1871, because of differences in crystalline form, is known as diaphorite (from διαφορά, “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, AgPbSb3S6, which is mined as a silver ore at Oruro in Bolivia.