Sphalerite is a polymorph with two minerals, wurtzite and matraite. The three are called polymorphs. Which means they have the same chemistry, (Zn, Fe)S or zinc iron sulfide. But they have different structures and therefore different shapes. Sphalerite is the more common mineral of the three. There is also an iron rich variety of sphalerite that is called Marmatite. Marmatite is not a commonly seen mineral because it is brilliant black like black sphalerite. So it is very often unrecognized. Marmatite is chemically a ferroan sphalerite. It contains, up to twenty percent iron in addition to zinc sulfide. Sphalerite comes in 2 types the black Sphalerite as mentioned before also called Black Jack and red commonly called Ruby Jack. This specimen is a dark Ruby Jack from The cumberland mine heading 16 S. 3 Carthage, Smith Co. Tennessee. the calcite crystals on this specimen are scalenohedrons. This specimen is way more interesting than what the camera can capture.