Although manganese does not occur alone in nature as a native element,
it makes up a part of many minerals and compounds. This element has an
important use in steel making, where it helps rid the steel of unwanted
substances, such as oxygen and sulfur, and, in addition, it is used to
make tough, hard, manganese steel for armor plate, railroad tracks,
safes, and steam shovels. Manganese has various uses outside the steel
industry. It is added to copper and nickel to make alloys, it is used in
the manufacture of dry-cell batteries, and (as manganese sulfate) it is
used as a fertilizer.
Manganese minerals and compounds, such as _braunite_, _hollandite_,
_pyrolusite_, and _wad_, occur in several counties in Texas. No large,
commercial deposits have been found here.
Some manganese compounds and minerals are covered with a soft, sooty
black material that will soil your fingers. This can help you recognize
these minerals; however, a few non-manganese minerals, such as some
chalcocite, also have a black coating that soils your fingers in a
similar way.
One of the manganese minerals, _braunite_, is a complex oxide of
manganese that contains silica. It has a submetallic luster and is dark
steel-gray or black. When rubbed across a streak plate, it leaves a
steel-gray or a black streak. This mineral is too hard to be scratched
by a pocket knife, but a piece of quartz or a steel file will scratch
it. Braunite has a specific gravity of 4.75 to 4.82. It has four
directions of cleavage that are parallel to the faces of a pyramid.
In the Spiller mine, about 15 miles northeast of Mason in Mason County,
masses of braunite occur as lens-shaped layers in Precambrian gneiss and
quartzite rocks. This braunite may have formed from another manganese
mineral (possibly manganese garnet) that was exposed at the earth’s
surface after the overlying rocks eroded away. As this other mineral
weathered, it may have altered into braunite, or the braunite could have
been deposited from solutions emanating from hot magmas before the great
thickness of overlying rock was removed.
The mineral variety _hollandite_ is a rare manganate of manganese and
barium. It has a metallic luster, and its color is silvery gray or
black. When you rub it across a streak plate, hollandite leaves a black
streak. It has a specific gravity of 4.7 to 5. Hollandite is rather
hard, but a steel file will scratch it.
[Illustration: Hollandite from Jeff Davis County, Texas.]
Hollandite occurs in western Jeff Davis County in west Texas at what is
called the Mayfield prospect. Here, it is found as rounded masses that
occur in a vein near a large fault in Lower Cretaceous limestone rocks.
Other manganese compounds, _pyrolusite_ and _wad_, are found in several
important deposits near the Pecos River in western Val Verde County.
_Pyrolusite_ is a manganese dioxide mineral. It is black, opaque, and so
soft that it rubs off on your fingers like soot. Pyrolusite may be
granular and massive or may be powdery. It also occurs as a fern-like
coating on rocks. _Wad_ is not really a mineral but is an impure,
dull-black or brownish-black mixture of manganese oxide, water, and
other substances. It can be soft enough to soil your fingers, or it can
be too hard to scratch with a pocket knife. Wad occurs in earthy or
compact masses or in crusts or stains on rocks.
In Val Verde County, the wad and pyrolusite are found mixed with soil,
clay, gravel, sand, and plant remains. This material fills cracks in
Lower Cretaceous limestones, it is scattered through gravels, and it is
deposited in low places at the surface. The manganese in these deposits
came from limestone rocks that have since weathered away. Rainwater
trickled into these rocks and dissolved the manganese minerals they
contained. This manganese was washed down toward the Pecos River and was
deposited as wad and pyrolusite.