Hematite
| Hematite |
|
| General |
| Category |
Oxide minerals |
Formula
(repeating unit) |
iron(III) oxide, Fe2O3, α-Fe2O3 |
| Strunz classification |
04.CB.05 |
| Crystal symmetry |
Trigonal hexagonal scalenohedral
H-M symbol: (32/m)
Space group: R3c |
| Unit cell |
a = 5.038(2) Å, c = 13.772(12) Å; Z = 6 |
| Identification |
| Color |
Metallic gray, dull to bright red |
| Crystal habit |
Tabular to thick crystals; micaceous or platy, commonly in rosettes;
radiating fibrous, reniform, botryoidal or stalactitic masses,
columnar; earthy, granular, oolitic |
| Crystal system |
Trigonal |
| Twinning |
Penetration and lamellar |
| Cleavage |
None, may show partings on {0001} and {1011} |
| Fracture |
Uneven to sub-conchoidal |
| Tenacity |
Brittle |
| Mohs scale hardness |
5.5–6.5 |
| Luster |
Metallic to splendent |
| Streak |
Bright red to dark red |
| Diaphaneity |
Opaque |
| Specific gravity |
5.26 |
| Optical properties |
Uniaxial (-) |
| Refractive index |
nω = 3.150–3.220, nε = 2.870–2.940 |
| Birefringence |
δ = 0.280 |
| Pleochroism |
O = brownish red; E = yellowish red |
| References |
[1][2][3] |
Hematite,
also spelled as haematite, is the
mineral form of
iron(III) oxide (Fe
2O
3), one of several
iron oxides. Hematite crystallizes in the
rhombohedral system, and it has the same
crystal structure as
ilmenite and
corundum. Hematite and ilmenite form a complete
solid solution at temperatures above 950 °C.
Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It is
mined as the
main ore of iron. Varieties include
kidney ore,
martite (
pseudomorphs after
magnetite),
iron rose and
specularite
(specular hematite). While the forms of hematite vary, they all have a
rust-red streak. Hematite is harder than pure iron, but much more
brittle.
Maghemite is a hematite- and magnetite-related oxide mineral.
Huge deposits of hematite are found in
banded iron formations. Gray hematite is typically found in places where there has been standing water or mineral
hot springs, such as those in
Yellowstone National Park in the
United States. The mineral can
precipitate
out of water and collect in layers at the bottom of a lake, spring, or
other standing water. Hematite can also occur without water, however,
usually as the result of
volcanic activity.
Clay-sized hematite crystals can also occur as a secondary mineral formed by
weathering processes in
soil, and along with other iron oxides or oxyhydroxides such as
goethite, is responsible for the red color of many
tropical, ancient, or otherwise highly weathered soils.
Etymology and history
Hematite in a scanning electron microscope, magnification 100x
The name hematite is derived from the
Greek word for blood
αἷμα haima because hematite can be red, as in
rouge, a powdered form of hematite. The color of hematite lends it well in use as a
pigment. The English name of the stone is derived from
Middle French: Hématite Pierre, which was imported from
Latin: Lapis Hæmatites, which originated from
Ancient Greek: αἱματίτης λίθος (haimatitēs lithos, “blood-red stone”).
Ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%.
[4] Red ochre contains unhydrated hematite, whereas
yellow ochre contains
hydrated hematite (
Fe2O3 •
H2O). The principal use of ochre is for tinting with a permanent color.
[4]
The
red chalk
writing of this mineral was one of the earliest in the history of
humans. The powdery mineral was first used 164,000 years ago by the
Pinnacle-Point man possibly for social purposes.
[5] Hematite residues are also found in old graveyards from 80,000 years ago. Near Rydno in
Poland and Lovas in
Hungary, palaeolitic red chalk mines have been found that are from 5000 BC, belonging to the
Linear Pottery culture at the
Upper Rhine.
Rich deposits of hematite have been found on the island of
Elba that have been mined since the time of the
Etruscans.
Jewelry
Hematite carving, 5 cm (2 in) long.
Hematite's popularity in jewelry was at its highest in Europe during the
Victorian era, and has since seen a strong resurgence in
North America, especially in the western
United States. Certain types of hematite or iron oxide rich clay, especially
Armenian bole has been used in
gilding. Hematite is also used in art such as
intaglio engraved gems.
Hematine is a synthetic material sold as
magnetic hematite.
[6]
Magnetism
Crystal structure of hematite
Hematite is an
antiferromagnetic material below the
Morin transition at 250 K, and a canted antiferromagnet or weakly
ferromagnetic above the Morin transition and below its
Néel temperature at 948 K, above which it is
paramagnetic.
The magnetic structure of a-hematite was the subject of considerable
discussion and debate in the 1950s because it appeared to be
ferromagnetic with a Curie temperature of around 1000 K, but with an
extremely tiny moment (0.002 µ
B). Adding to the surprise was a
transition with a decrease in temperature at around 260 K to a phase
with no net magnetic moment. It was shown that the system is essentially
antiferromagnetic, but that the low symmetry of the cation sites allows
spin–orbit coupling to cause
canting of the moments
when they are in the plane perpendicular to the c axis. The
disappearance of the moment with a decrease in temperature at 260 K is
caused by a change in the
anisotropy which causes the moments to align along the c axis. In this configuration, spin canting does not reduce the energy.
[7][8]
The magnetic properties of bulk hematite differ from their nanoscale
counterparts. For example, Morin transition temperature of hematite
decreases with decrease in the particle size. The suppression of this
transition have also been observed in some of the hematite nanoparticles
and the presence of impurities, water molecules and defects in the
crystals were attributed to the absence of Morin transition. Hematite is
part of a complex solid solution oxyhydroxide system having various
contents of water, hydroxyl groups and vacancy substitutions that affect
the mineral's magnetic and crystal chemical properties.
[9] Two other end-members are referred to as protohematite and hydrohematite.
Iron from mine tailings
Hematite is present in the waste
tailings of
iron mines. A recently developed process,
magnetation, uses huge magnets to glean waste hematite from old mine tailings in
Minnesota's vast
Mesabi Range iron district.
[10]
Discovery on Mars
Image mosaic from the Mars Exploration Rover Microscopic Imager shows Hematite
spherules partly embedded in rock at the Opportunity landing site. Image is ca. 5 cm (2 in) across.
The spectral signature of hematite was seen on the planet
Mars by the infrared
spectrometer on the
NASA Mars Global Surveyor ("MGS") and
2001 Mars Odyssey spacecraft in orbit around Mars.
[11] The mineral was seen in abundance at two sites
[12] on the planet, the
Terra Meridiani site, near the Martian equator at 0° longitude, and the second site
Aram Chaos near the
Valles Marineris.
[13] Several other sites also showed hematite, e.g., Aureum Chaos.
[14]
Because terrestrial hematite is typically a mineral formed in aqueous
environments, or by aqueous alteration, this detection was
scientifically interesting enough that the second of the two
Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designated
Meridiani Planum. In-situ investigations by the
Opportunity rover showed a significant amount of hematite, much of it in the form of small
spherules that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently
concretions
formed from a water solution. "Knowing just how the hematite on Mars
was formed will help us characterize the past environment and determine
whether that environment was favorable for life," .. "One big question,
of course, is whether life ever started on Mars. This mission probably
won't tell us that, but it may well lead to future mission that can
answer that question."
[15]
See also
References
- ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W. and Nichols, Monte C. (ed.). "Hematite" (PDF). Handbook of Mineralogy. III (Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209724. Retrieved December 5, 2011.
- ^ Hematite. Webmineral.com. Retrieved on 2011-06-22.
- ^ Hematite. Mindat.org. Retrieved on 2011-06-22.
- ^ a b "Ochre". Industrial Minerals. Minerals Zone. Retrieved 2008-04-29.
- ^ Researchers find earliest evidence for modern human behavior in South Africa. Eurekalert.org (2007-10-17). Retrieved on 2011-06-22.
- ^ Magnetic hematite. Mindat.org (2011-06-18). Retrieved on 2011-06-22.
- ^ Dzyaloshinsky, I. (1958). "A thermodynamic theory of "weak" ferromagnetism of antiferromagnetics". Journal of Physics and Chemistry of Solids 4 (4): 241. Bibcode:1958JPCS....4..241D. doi:10.1016/0022-3697(58)90076-3.
- ^ Moriya, T. (1960). "Anisotropic Superexchange Interaction and Weak Ferromagnetism". Phys. Rev. 120: 91. Bibcode:1960PhRv..120...91M. doi:10.1103/PhysRev.120.91.
- ^ Dang,
M.-Z.; Rancourt, D.G.; Dutrizac, J.E.; Lamarche, G. and Provencher, R.
(1998). "Interplay of Surface Conditions, Particle Size, Stoichiometry,
Cell Parameters, and Magnetism in Synthetic Hematite-like Materials". Hyperfine Interactions 117: 271–319. Bibcode:1998HyInt.117..271D. doi:10.1023/A:1012655729417.
- ^ Redman, Chris. (2009-05-20) The Next Iron Rush, Fortune Magazine, May 25, 2009, pp. 86–90. Money.cnn.com. Retrieved on 2011-06-22.
- ^ NASA MGS TES Press Release, May 27, 1998 "Mars Global Surveyor TES Instrument Identification of Hematite on Mars"
- ^ Bandfield, J.L. (2002). "Global mineral distributions on Mars". J. Geophys Res. 107. Bibcode:2002JGRE..107.5042B. doi:10.1029/2001JE001510.
- ^ Glotch,
T. D., and Christensen, P. R. (2005). "Geologic and mineralogic mapping
of Aram Chaos: Evidence for a water-rich history". J. Geophys. Res. 110: E09006. Bibcode:2005JGRE..11009006G. doi:10.1029/2004JE002389.
- ^ Glotch, T. D., Rogers, D. and Christensen, P. R. (2005). "A Newly Discovered Hematite-Rich Unit in Aureum Chaos: Comparison of Hematite and Associated Units With Those in Aram Chaos". Lunar and Planetary Science Conference XXXVI. Bibcode:2005LPI....36.2159G. Archived from the original on 2008-12-17.
- ^ Hematite. NASA. Last Updated: 12 Jul 2007
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