With the addition of manganese it forms a series with benavidesite.[1] It is a dark grey metallic mineral which forms acicular prismatic monoclinic crystals. It is soft with a Mohs hardness of 2.5 and has a specific gravity of 5.5 - 5.6.[2] It is one of the few sulfide minerals to form fibrous or needle like crystals. It can also form large prismatic crystals similar to stibnite with which it can be associated.