SPHALERITE (30)
SPHALERITE, zinc sulfide, is a major ore of zinc. It has a resinous luster and a white, yellow, or brown streak. Illinois sphalerite is generally yellow, yellowish brown, reddish brown, or brownish black. It is of medium weight, brittle, can be scratched by a piece of window glass but not by a penny. It is commonly opaque but may be translucent on thin edges.
Sphalerite is mined with galena in northwestern Illinois and in extreme southern Illinois with galena and fluorite. Small crystals occasionally are found in limestones and as crystalline masses in clay-ironstone concretions.