It forms nice crystals that can be arranged into rosette-like clusters with projecting rhombohedral terminations. Clusters can be attractive and good specimens command large prices, mostly because of the rarity of the mineral. Gratonite is a sulfosalt, a segment of sulfides where the arsenic acts more like a metal than a non-metal and occupies a position where it is bonded to sulfurs. Color is a dark lead gray. Luster is metallic.
Crystals are opaque.
Clusters can be found in rosette-like aggregates, also massive. Streak is gray. Notable Occurrences are limited to the Excelsior Mine, Cerro de Pasco, Peru. Best Field Indicators are crystal habit, locality, color and density.