Reddish and silvery white, sulphidic ore containing cobalt and arsenic, with a metallic luster (main component CoAsS, Fig. 1). 

Cobaltite has a hardness of 5.5 (Mohs) and a density of 6.0 - 6.4 g/cm3. In an experiment for proof, using a blowpipe the mineral is melted to form a gray lump; on the charred material arsenic(III) oxide bloom is formed, in nitric acid the material dissolves to a pink solution and precipitates of sulfur and arsenic(III) oxide.