Sphalerite

Sphalerite is an ore—a mineral of economic value—that was once mined in southeastern Kansas for its zinc content. It is also called zinc blende, blende, blackjack, and mock lead. Sphalerite crystals are usually shaped like triangular pyramids, with three sides and a base. Because it has good cleavage in six directions, sphalerite will break into 12-sided blocks.

Some sphalerite is found as massive deposits varying from coarse to fine grained. The best specimens in Kansas were found in the lead and zinc mines of Cherokee County.

Chemical compound: zinc sulfide
Chemical formula: ZnS (Zn = zinc, S =  sulfur)
Color: nearly colorless, but can be brown, yellow, black, or dark red due to impurities
Streak: white to dark brown
Specific gravity: 4
Luster: brilliant resinous or metallic
Hardness: 3.5–4
Amount of transparency: transparent to translucent, opaque when iron-rich