Allargentum

Allargentum is a mineral from the class of antimonides, superclass of sulfides and sulfosalts (sometimes ascribed to the natural elements and alloys class), with formula written as Ag_1-xSb_x, where x = 0.09–0.16. This moderately rare mineral is found in silver ores and is therefore named from the Greek ἄλλος (allos, "another") and the Latin argentum ("silver"). Its Vickers hardness is 172–203.