Sphalerite is a mineral that is the chief ore of Zinc. It consists mainly of Zinc Sulfide in crystalline form but almost always contains valuable Iron. When the Iron content is high, it is an opaque black variety called Marmatite. It is usually found in association with Galena, Pyrite, Calcite, Dolomite and Fluorite. It is usually yellow, brown or gray to gray-black in color and may have a shiny or dull luster or sheen.