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Tantalite
Mineral Facts:
Chemical
Formula: (Fe,Mn)Ta2O6
The tantalate
of ferrous iron and manganese
with some niobium,
containing from 60 to 80 percent Ta2O5. The mineral often contains small amounts of
tin, tungsten, etc.
Colors:
iron-black,
frequently iridescent.
The streak is dark red to black.
Hardness:
6
Density:
7 to 8
Density is variable based on chemical make up and amounts of impurities.
High tantalum content leads to greater density.
Cleavage:
The cleavage is
distinct parallel to (010).
Crystallography: Orthorhombic
Habit of crystals
frequently is in the form of prismatic crystals. is
short prismatic; often in square prisms because of prominent development of
the vertical pinacoids. Terminated by basal plane, pyramids and domes;
frequently
complex. At times in heart-shaped contact twins. Crystallized and in
parallel crystal groups. It is also frequently granular and massive.
Luster:.
submetallic luster
and opaque. |
Tantalite Tantalum ore |
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Composition, Structure and
Associated Minerals:
Tantalite and
columbite are not uncommon as constituents of cassiterite bearing pegmatite
veins, but in most cases the amounts found are small. Tantalite is found at
many of the localities for columbite and also at several other places.
A part of the
tantalum in tantalite is almost invariably replaced by the closely allied
metal niobium, and when the amount of the latter exceeds the former, the
mineral is known under the name of columbite.
Tantalite is the form of this
mineral which is principally a mixture of tantalates with a minimum of
niobium. When the tantalite is composed almost exclusively of the manganese
molecule (with little iron), it is known as manganotantalite.
Tantalite occurs in
granite rocks and in pegmatite veins, associated with
quartz, feldspar, mica,
tourmaline,
beryl,
spodumene,
casseterite, samarskite,
wolframite, microlite,
monazite, etc.
Tantalite has been found in Egypt, Brazil
Namibia, Nigeria, Madagascar, Canada and Europe. Notable
localities for its occurrence are the west coast of Greenland; Bodenmais,
Bavaria; llmen Mountains, Siberia; Western Australia (where the variety is manganotantalite);
Standish, Maine; Haddam, Middletown and Branchville, Connecticut; in Amelia
County, Virginia; Mitchell County, North Carolina; Black Hills, South
Dakota; near Canon City, Colorado. Some specimens
exhibit weak radioactivity.
Identification
and Diagnostics
Tantalite is infusible before the
blowpipe and
insoluble in acids.
Composition variable, when significant niobium is present, fusion with borax
where the bead is dissolved in hydrochloric acid; if the solution
is then boiled with tin gives a blue color (positive test for niobium). The mineral
is also partially decomposed
when evaporated to dryness with H2SO4, forming a white compound that changes
to yellow. When this residue is boiled with HC1 and metallic zinc a blue
solution results. The mineral also gives reactions for iron and manganese.
When tantalite is fused
with KHSO4 and treated with dilute HC1 give a yellow solution and a heavy
white precipitate, which, on treatment with metallic zinc or tin, assumes a
deep blue color. When diluted with water the blue color of the tantalate
solution disappears, while that of the columbate solution remains.
Generally when fused in an oxidizing
flame with sodium carbonate it gives an opaque bluish green bead. Fused with
sodium carbonate on charcoal in the reducing flame it yields a magnetic mass.
Tantalite is normally recognized
by its black color, submetallic streak and high specific gravity.
Tantalite may easily be
confused with black tourmaline, ilmenite and wolframite. From tourmaline,
tantalite is distinguished by crystallization, high specific gravity and
luster; from wolframite by its less perfect cleavage and by the reaction
with aqua regia; from ilmenite by the test for the presence of titanium.
Localities
The only important
tantalum ore mineral is tantalite. Many other minerals contain tantalum, but
they are either too rare or contain amounts too small to make them of any
value in competition with tantalite. By increase in the amount of columbium,
tantalite grades into
columbite, in typical specimens of which niobium is
greatly in excess of tantalum; such columbite is of no value as tantalum
ore, which requires to contain at least 60 per cent, of Ta2O5, not more than
3 per cent, of Cb2 5, and no chromium.
The only source
of any commercial importance is the mineral tantalite which is sold on a
basis of 60 percent Ta2O5 and which is chiefly obtained from the
neighborhood of Greenbushes, in Western Australia, where it also occurs in
association with cassiterite
and wolframite. The world's largest reserves are in Brazil. However, seventy
five percent of world production has come from Western Australia. Ethiopia,
Mozambique and China also produce some tantalite.
Tantalum Uses:
The chief use of
tantalum is in the manufacture of small sized electrolytic capacitors and
high power resistors. Because of the size and
weight advantages, tantalum capacitors are attractive for many small
portable electronic devices including cell phones, personal computers and
pad screens. The production of electronic parts consumes the vast majority
of all tantalum production.
Metallic tantalum has also been
used in the manufacture of filaments of electric lamps, but very little is
required for this purpose. One pound (avoirdupois) of the metal suffices for
the manufacture of over 20,000 lamps, and it is easy to understand that the
requirements for this purpose alone are not sufficient to create a steady
demand for the ore. Experiments have been made to test the utility of
tantalum as a steel-hardener, but hitherto there appears not to have been
any considerable demand for this purpose. The chief localities in the US are
in the Black Hills of South Dakota, U.S.A., and world wide at Greenbushes
and Wodgina in Western Australia, from both of which regions tantalite for
economic use has been obtained.
SOUTH DAKOTA. In the Black Hills of South Dakota, pegmatites carrying
tantalite, columbite, cassiterite, and wolframite traverse pre-Cambrian
schists. The pegmatites are offshoots from the pre-Cambrian intrusions of
granite which form the central mass of the Black Hills.
The tantalite occurs abundantly near Keystone, where it has been mined.
WESTERN AUSTRALIA. Tantalite has been mined at Greenbushes and Wodgina in
Western Australia. Here also the tantalite (chiefly
mangano-tantalite containing little or no iron) occurs in pegmatites
associated with granites that are intrusive in pre-Cambrian schists.
The output is small and irregular, as there is little demand. The total
output during a period of about 15 years has amounted to only about
150 tons, and most of this has been obtained from the surface residual and
alluvial deposits that occur in the neighborhood of the pegmatites.
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