What Is Chromate?
Commonly found in meteorites and
metamorphic rocks such as serpentites
Name: Chromite
Chemistry: FeCr2O4
Color: Deep dark black, brownish black
Hardness: 5.5
Specific Gravity: 4.5-4.8
Crystals: Isometric
Accompanied by: Anorthite, Biotite,
Magnetite, Magnesium, Olivine,
Serpentine, Talc, Uvarovite, Pyroxenes
Fracture: Uneven / conchoidal
Luster: Metallic to greasy
Cleavage: None
Used in a wide range of industrial
process. Natural Chromite contains some
magnesium. It is weakly magnetic and an
octahedral parting is sometimes seen
• Chemical Formula: FeCr2O4, Iron
Chromium Oxide.
• Class: Oxides and Hydroxides
• Group: Spinel
• Uses: The principle ore of chromium,
as a refractory component, as a dye and
as mineral specimens.
• Specimens
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.
Chromite Packing
All grades of Chromite are available in
various types of packaging:
1. 1 Ton Jumbo bags
2. 25kg package for powder
Chromate Physical Properties
| Hardness |
5.5 |
| Specific gravity |
4.5 - 4.8 (average for
metallic minerals) |
| Color |
Brownish black to a deep
dark black |
| Crystal Habits |
Include octahedrons often
with dodecahedral faces modifing
the edges of the octahedron to
the point of rounding the
crystal. Well formed crystals
are rare and chromite is usually
found massive or granular. |
| Luster |
Metallic to greasy |
| Streak |
Brown |
| Transparency |
Crystals are opaque |
| Crystal System |
Isometric; 4/m bar 3 2/m |
| Cleavage |
Absent |
| Fracture |
Conchoidal |
| Other Characteristics |
Weakly magnetic and an
octahedral parting is sometimes
seen. |
| Associated Minerals |
Include olivine, talc,
serpentine, uvarovite,
pyroxenes, biotite, magnetite
and anorthite. |
| Best Field Indicators |
Crystal habit, streak,
associations with ultra-basic
minerals and parting. |
General Properties of Chromate Fe++Cr2O4
| Composition |
Molecular Weight =223.84 gm |
|
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Chromium |
46.46 % |
Cr |
67.90 %Cr2O3 |
| |
Iron |
124.95 % |
Fe |
32.10 % FeO |
| |
Oxygen |
28.59 % |
O |
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______ |
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______ |
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100.00 % |
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100.00 % = TOTAL OXIDE |
Empirical Formula: Fe2+Cr2O4
Environment: Cummulate mineral found in
ultramafic portions of layered mafic
intrusions. Common in meteorites.
IMA Status: Valid Species (Pre-IMA)
Name Origin: Named after its chemical
composition.
Synonym: Chrome iron ore, Chromic iron,
Ferrichromite-magnetic, altered, ICSD 20819
chromite Crystallography
Cell Dimensions: a = 8.36, Z = 8; V =
584.28 Den(Calc)= 5.09
Crystal System: Isometric -
HexoctahedralH-M Symbol (4/m 3 2/m)
Space Group: F d3m
X Ray Diffraction: By Intensity (I/Io):
2.52(1), 1.46(0.9), 1.6(0.9).
Optical Properties of Chromate
Gladstone-Dale: CI meas= 0.092 (Poor) -
where the CI = (1-KPDmeas/KC)
CI calc= 0.145 (Poor) - where the CI =
(1-KPDcalc/KC)
KPDcalc= 0.22,KPDmeas= 0.2336,KC= 0.2573
Optical Data: Isotropic, n=2.08-2.16.
RL Color: Gray-white with a brownish
tint and brownish red internal
reflections.
RL Pleochroism: None
Calculated Properties of Chromate
| Electron Density |
ſelectron=4.54 gm/cc
Note: ſChromite =4.80 gm/cc. |
| Photoelectric |
PEChromite = 18.28 barns/electron
U=PEChromite x ſelectron= 83.03
barns/cc. |
| Radioactivity |
GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Chromite is Not Radioactive |
Chromate Classification
| Dana Class |
7.2.3.3 (7) Multiple Oxides
(7.2)(A+ B++)2 X4 Spinel group
(7.2.3)(Chromium subgroup)
7.2.3.1
Magnesiochromite MgCr2O4
F d3m 4/m 3 2/m
7.2.3.2 Manganochromite
(Mn,Fe)(Cr,V)2O4 F d3m
4/m 3 2/m
7.2.3.3 Chromite FeCr2O4
F d3m 4/m 3 2/m
7.2.3.4 Nichromite (Ni,Co,Fe)(Cr,Fe,Al)2O4
F d3m 4/m 3 2/m
7.2.3.5 Cochromite (Co,Ni,Fe)(Cr,Al)2O4
F d3m 4/m 3 2/m
7.2.3.6 Zincochromite
ZnCr2O4 F d3m 4/m 3 2/m |
|
| Strunz Class |
IV/B.03-20 IV - Oxides
V/B - Oxides with metal: oxygen
= 3:4 (spinel type M3O4 and
related) Chromite-Spinels
IV/B.03 - Spinel group,
Magnesio-chromite -
Zinco-Chromite series
IV/B.03-10
Magnesiochromite MgCr2O4
F d3m 4/m 3 2/m
IV/B.03-20 Chromite
FeCr2O4 F d3m 4/m 3 2/m
IV/B.03-30
Manganochromite (Mn,Fe)(Cr,V)2O4
F d3m 4/m 3 2/m
IV/B.03-40 Cochromite (Co,Ni,Fe)(Cr,Al)2O4
F d3m 4/m 3 2/m
IV/B.03-50 Nichromite (Ni,Co,Fe)(Cr,Fe,Al)2O4
F d3m 4/m 3 2/m
IV/B.03-60 Zincochromite
ZnCr2O4 F d3m 4/m 3 2/m
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|
 Spinel Group
The Spinel group is composed of the
crystal structure.
Recommended Filled of Application
| Kind of powder |
Talc |
Mica |
Kaolin |
Red Iron oxide |
Fluorine |
Dolomite |
Calcite |
Bentonite |
Barite |
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