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Pyrolusite Mineral Facts:
Chemical Formula: MnO2
Manganese Dioxide, a principal ore of manganese. Commonly contains a
little water.
Colors:
Iron-black color and streak.
Hardness:
2-2.5, often soiling the fingers.
Density: 4.75
Cleavage:
Perfect on 110, Splintery fracture.
Crystallography: Hexagonal
Crystals are radiating columnar to fibrous, also granular or massive;
often in reniform coats. Crystals probably always pseudomorphous after
manganite.
Luster:.
Metallic and opaque.
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Composition,
Structure and Associated Minerals:
Pyrolusite is a secondary mineral. Manganese is dissolved out
of the crystalline rocks, in which it is almost always present in small
amounts, and redeposited under various conditions, chiefly as pyrolusite.
Dendritic coatings of pyrolusite are frequently observed on rock surfaces,
coating pebbles, etc. Nodular deposits of pyrolusite are found on the sea
bottom. Nests and beds of manganese ores are found inclosed in residual
clays, derived from the decay of manganiferous limestones. As the rock has
weathered and its soluble constituents -been taken away, the manganese
content has
been concentrated in nodules and masses composed chiefly of
pyrolusite. Also found in veins with
quartz
and various metallic
minerals.
Identification and Diagnostics
The manganese minerals are easily distinguished from other minerals by
the violet color they give to the borax bead and by the green product
obtained when they are fused with sodium carbonate. Gives oxygen in closed
tube, and
which will cause a splinter of charcoal to ignite when placed in
tube above the mineral and heated. In hydrochloric acid, chlorine gas
evolved. Pyrolusite is distinguished from manganite by its physical
properties, and from polianite
by its softness.
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Occurrence,
Localities and Origins:
Pyrolusite, together with the
other manganese ores with which it is mixed, is the source of nearly all the
manganese compounds employed in the industrial arts. Some of the ores,
moreover, are argentiferous and others contain zinc. From these silver and
zinc are extracted. The
most important use of the mineral is in the iron industry. In this industry,
however, much of the manganese employed is obtained from manganiferous iron
ores. The alloys spiegeleisen and ferro-manganese are employed very largely
in the production of an iron used in the steel industry for casting car
wheels and other items. It is also employed in making various alloys with
copper, zinc, aluminium, tin, lead, etc. It is extremely hard and tough. The
manganese minerals are also used in glass factories to neutralize the green
color imparted to glass by the ferruginous impurities in the sands from
which the glass is made. Pyrolusite is also used as a decolorizer of glass,
and in electric cells and batteries. Manganese is also used as a coloring
material in bricks, pottery, glass, etc. giving black, brown and violet
colors to pottery. Some of its salts are used to make potassium
permanganate, while some are valuable mordants.
Pyrolusite has been mined at
Elgersberg, near Ilmenau in Germany; at Vorder Ehrensdorf and at Flatten in
the Czech Republic also in
Australia, Japan, India and New Brunswick, Nova Scotia. In the US it has
been mined at Cartersville, Ga.; at Batesville, Ark., California and in the
Valley of Virginia. A manganiferous
silver ore
containing considerable quantities of pyrolusite was mined in the Leadville
district, Colorado, and large quantities of manganiferous iron ores are
obtained in the Lake Superior region.
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