Galena commonly occurs in Missouri as a cavity filling in crushed limestone or chert, or as a replacement in limestone or dolomite, or in shale, so that a large quantity of practically worthless enclosing rock (gangue) must be taken out in order to obtain the desired galena. If a person desires to estimate the value of his galena (lead) prospect by having an analysis or assay made of his ore, he must include in his sample the gangue rock that would of necessity have to be taken out when mining his ore. Too often persons carefully select for analysis a choice galena specimen which may run over 80% lead, only to find that as a practical mine product it would be reduced to less than 5% lead in all the rock which also would have to be taken out.
After a galena ore is mined it is customarily crushed and the galena removed from the gangue by a gravity-separation process which takes advantage of the difference in “heaviness” (specific gravity) between galena (7.5) and limestone (calcite) or chert (2.7-2.6), or by a froth flotation process in which the galena is preferentially wetted and carried off by an oily froth or foam. The galena concentrate is roasted to burn out the sulphur, reduced by carbon, and smelted to metallic lead. The origin of some Missouri lead deposits is debatable, but the writer believes the most reasonable explanation to be that warm, chemically active waters arose from an igneous body below and carried to the place of deposition the lead which they held in solution.
Missouri is one of the leading producers of lead in the world from its Flat River, Fredericktown, Joplin, and central Missouri districts, from which in 1941 lead concentrates having a value of over $15,000,000 were produced.
Sphalerite
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 southwestern 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 southeastern Missouri chat, which is largely dolomite.
Sphalerite from near Joplin.
Barite (“Tiff”)
Barite (“Tiff” in southeast Missouri, Heavy Spar, Barytes) occurs in Missouri predominantly as a white, quite heavy, soft, non-metallic mineral which has a high luster on a freshly broken surface. Slightly bluish “glass” barite or “glass tiff” has been found in smaller quantity with the more abundant, opaque white material. The glassy barite may superficially resemble calcite or selenite gypsum, but in distinction, barite breaks or cleaves to surfaces joining at right angles and does not effervesce with acid, whereas calcite does effervesce in acid and cleaves at oblique angles (rhombohedral cleavage). Gypsum is so soft that it can be scratched very easily with the thumb-nail, whereas barite is scratched with difficulty, if at all, by the thumb-nail. Notably, again, barite is “heavy,” with a specific gravity of about 4.5, whereas calcite, gypsum, limestone, and chert are “lighter,” with a specific gravity of about 2.6 to 2.7. Barite has the composition barium sulphate, BaSO₄, of which barium oxide constitutes 65.7 per cent.