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.