Sulfosolids represent the third class that includes a diverse and relatively large group of minerals with a complex anion, differing from minerals of the second class from which it was recently separated as a distinct entity. The term "sulfosolids" was originally proposed to indicate that the minerals of this group are salts of a series of acids in which sulfur replaces oxygen. Since such acids are hypothetical, this sometimes led to confusion in explaining this class of minerals. Despite this, the term sulfosolids has remained to describe a specific type of non-oxidized minerals that contain sulfur and structurally differ from sulfides.

Simply put, sulfosolids differ from sulfides in that in sulfides containing a metalloid such as antimony, arsenic, or bismuth, it replaces the position of sulfur, whereas in sulfosolids, the metalloid replaces the position of the metal and binds with sulfur.

The older Croatian term for minerals of this group is "blue stones" due to their characteristic lead-gray (blue) color. The most famous representatives of the sulfosolid class are pyrargyrite, proustite, and a series of mixed crystals whose final members are tetrahedrite and tennantite, which are also ore minerals.