The members of this economically important class are very interesting and often found exhibiting wonderful images under petrographic polarizing light microscopes. The major ores of important metals such as silver, copper and lead belongs to this Sulfides Mineral Class. And as ore minerals, they are usually found showing majestic appearance when evaluated with the aid of ore polarizing microscopes. Strong generalities exist in this Sulfides Mineral Class. Almost all members of this wonderful mineral class are found opaque in appearance, exhibiting metallic luster in reflected light of the geological polarizing light microscopes, and with crystals that are generally sectile. Sulfides are generally soft to average in hardness and they are usually found having high densities. They are igneous in origin and they are commonly found leaving black or dark colored streaks when rubbed on a white porcelain streak plate. There are only few vitreous and transparent members that belong to this Sulfides Mineral Class. Among these are cinnabar, realgar and orpiment that usually tend to break the mold.
The members of the Telluride, Antimonide, Selenide, and Arsenide Subclasses are usually found exhibiting very similar properties to the more common sulfide minerals. That is why they are all classified under this mineral class. Because selenium, antimony, tellurium, arsenic, or bismuth are usually found having similar sizes, charges and ionic strengths, the whole or partial supplanting of sulfur by either of these elements is very much possible. The minerals that are found having no appreciable sulfur are the only ones included in these subclasses. If there is enough sulfur found in the formula of the treated mineral, then it is regarded as normal sulfide.
The case of Sulfosalts is different. Sulfosalts is actually a large segment of the sulfide class whose difference from the other sulfides lies in the position of the semi-metal ions. In most ordinary sulfides that contain a semi-metal such as arsenic, antimony or bismuth, they substitute in the sulfur positions. But in the case of sulfosalts, they substitute for the metal ions and bond with the sulfurs. The term sulfosalts came from the theory that these minerals were salts of acids in which the oxygens can be replaced by sulfurs. Although this theory is not considered credible, the word sulfosalts still persists nowadays.
