Chromite
Iron
Chromium Oxide
FeCr2O4
The principle ore of chromium, as a refractory component, as a dye
and as mineral specimens.
The Present Scenario
Notable Occurrences is several mines in North Carolina, Montana,
Maryland, Oregon, Texas, California and Wyoming, USA also found in
Turkey; South Africa; Philippines and Russia.
Chromite
is the most important ore of chromium from which it derives its name.
Chromium is an important metal and has a wide range of industrial
uses.
Chromite forms in deep ultra-mafic magmas and is one of the first
minerals to crystallize. It is because of this fact that chromite is
found in some concentrated ore bodies. While the magma is slowly
cooling inside the Earth's crust, chromite crsytals are forming and
because of their density, fall to the bottom and are concentrated
there.
Although its primary origin is ultra-mafic rocks such as peridotites,
chromite is also found in metamorphic rocks such as serpentites.
Chromite, as is indicated by its early crystallization is resistant to
the altering affects of high temperatures and pressures. Thus it is
capable of going through the metamorphic processes unscathed, while
other minerals around it are being altered to serpentine, biotite and
garnets. This characteristic also explains chromites use as a
refractory component in the bricks and linings of blast furnaces.
Usually magnesium is present in chromite substituting for the iron
and in fact a solid solution series exists between chromite and the
much rarer mineral magnesiochromite. All chromite specimens in nature
contain some magnesium, likewise all natural magnesiochromites contain
some iron. Magnesiochromite is grayer in color and in streak and has a
slightly lower density than chromite at a specific gravity of 4.2 to
4.4.
| Hardness |
Associated Minerals |
Chemical/Typical
composition |
Colour |
characteristics |
Luster |
Field Indicators |
| 5.5 |
olivine
talc
serpentine
uvarovite
pyroxenes
biotite
magnetite
anorthite |
Oxides and Hydroxides |
brownish black to a deep dark black |
Weakly magnetic and an octahedral
parting is sometimes seen |
metallic to greasy |
crystal habit, streak, associations
with ultra-basic minerals and parting |
Uses
The following uses for chromium are gathered from a number of sources
as well as from anecdotal comments. I'd be delighted to receive
corrections as well as additional referenced uses (please use the
feedback mechanism to add uses).
- used
to harden steel, to manufacture stainless steel, and to form alloys
- used
in plating to produce a hard, beautiful surface and to prevent
corrosion.
- used
to give glass an emerald green colour. It is responsible for the
green colour of emeralds and the red colour of rubies
- wide
use as a catalyst
- dichromates
such as K2Cr2O7 are oxidising
agents and are used in quantitative analysis and also in tanning
leather
- lead
chromate as chrome yellow is a pigment
- compounds
are used in the textile industry as mordants
- used
by the aircraft and other industries for anodising aluminium
- the
refractory industry uses chromite for forming bricks and shapes, as
it has a high melting point, moderate thermal expansion, and stable
crystalline structure
- tanning
leather
|
