Sphalerite (locally called Jack, Rosin Jack, Black Jack, Ruby Jack,
Zinc, Rosin Spar) is a tan-brown, resinous, brown or brownish black
mineral having a very high luster on its broken (cleavage) surfaces.
Much of it so strongly resembles lump rosin that the term “Rosin Jack”
is truly descriptive. Less commonly, a ruby red variety occurs as
crystals perched on other sphalerite or on waste rock. Sphalerite is
readily scratched with steel. Its chemical composition is zinc sulphide,
ZnS—zinc 67 per cent, sulphur 33 per cent—and it is an important ore of
zinc.
Sphalerite occurs abundantly in the mining district of southwest
Missouri, but small, non-commercial amounts of it have been found
through an area extending even north of the Missouri River. At the
mines, after the ore and rock are taken out, they are crushed and
separated, the ore going to the smelter and the rock to tailings piles.
Under the old milling process employed in south_western_ Missouri,
thousands of tons of coarse tailings, largely chert, were poured onto
huge “chat” piles, many of which remain as a low-priced by-product for
some one to put to use. This chat differs mineralogically from the
south_eastern_ Missouri chat, which is largely dolomite.
[Illustration: Sphalerite from near Joplin.]