Hematite


Hematite
Hematite

Hematite (blood ore) from Michigan (unknown scale)
General
Category Oxide minerals
Chemical formula iron(III) oxide, Fe2O3, α-Fe2O3
Strunz classification 04.CB.05
Identification
Color Metallic gray to red
Crystal habit Tabular to thick crystals
Crystal system Trigonal – hexagonal scalenohedral
Cleavage None
Fracture Uneven to sub-conchoidal
Mohs scale hardness 5.5 – 6.5
Luster Metallic to splendent
Streak Bright red to dark red
Specific gravity 4.9 – 5.3
Refractive index Opaque
Pleochroism None
References [1][2]

Hematite, also spelled as haematite, is the mineral form of iron(III) oxide (Fe2O3), 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. Grey 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.

Contents

Etymology and history

Hematite in a scanning electron microscope, magnification 100x
Close-up of hematitic banded iron formation specimen from Upper Michigan. Scale bar is 5.0 mm.
Cypro-Minoan cylinder seal (left) made from hematite with corresponding impression (right), approximately 14th century BC

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%.[3] Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite (Fe2O3H2O). The principal use of ochre is for tinting with a permanent color.[3]

The red chalk winning of this mineral was one of the earliest in history of mankind. The powdery mineral was first used 164,000 years ago by the Pinnacle-Point man obviously for social differentiation.[4] 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 till 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.[5]

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 µB). 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.[6][7]

Hematite is part of a complex solid solution oxyhydroxide system having various degrees of water, hydroxyl group, and vacancy substitutions that affect the mineral's magnetic and crystal chemical properties.[8] 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.[9]

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.[10] The mineral was seen in abundance at two sites[11] on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris.[12] Several other sites also showed hematite, e.g., Aureum Chaos.[13] 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." [14]

See also

References

  1. ^ Hematite. Webmineral.com. Retrieved on 2011-06-22.
  2. ^ Hematite. Mindat.org. Retrieved on 2011-06-22.
  3. ^ a b "Ochre". Industrial Minerals. Minerals Zone. http://www.mineralszone.com/minerals/ochre.html. Retrieved 2008-04-29. 
  4. ^ Researchers find earliest evidence for modern human behavior in South Africa. Eurekalert.org (2007-10-17). Retrieved on 2011-06-22.
  5. ^ Magnetic hematite. Mindat.org (2011-06-18). Retrieved on 2011-06-22.
  6. ^ I. Dzyaloshinsky (1958). "A thermodynamic theory of "weak" ferromagnetism of antiferromagnetics". Journal of Physics and Chemistry of Solids 4 (4): 241. doi:10.1016/0022-3697(58)90076-3. 
  7. ^ T. Moriya (1960). "Anisotropic Superexchange Interaction and Weak Ferromagnetism". Phys. Rev. 120: 91. doi:10.1103/PhysRev.120.91. 
  8. ^ M.-Z. Dang, D.G. Rancourt, J.E. Dutrizac, G. Lamarche, and R. Provencher (1998). "Interplay of Surface Conditions, Particle Size, Stoichiometry, Cell Parameters, and Magnetism in Synthetic Hematite-like Materials". Hyperfine Interactions 117: 271–319. doi:10.1023/A:1012655729417. 
  9. ^ 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.
  10. ^ NASA MGS TES Press Release, May 27, 1998 "Mars Global Surveyor TES Instrument Identification of Hematite on Mars"
  11. ^ Bandfield, J.L. (2002). "Global mineral distributions on Mars". J. Geophys Res. 107. doi:10.1029/2001JE001510. http://tes.asu.edu/mineral_map/bandfield_minmap.pdf. 
  12. ^ Glotch, T. D., and P. R. Christensen (2005). "Geologic and mineralogic mapping of Aram Chaos: Evidence for a water-rich history". J. Geophys. Res. 110: E09006. doi:10.1029/2004JE002389. 
  13. ^ T. D. Glotch, D. Rogers, and P. R. Christensen, 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, 2005
  14. ^ Hematite. NASA. Last Updated: 12 Jul 2007

External links


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Synonyms:

Look at other dictionaries:

  • Hématite — Catégorie IV : oxydes et hydroxydes[1] Hématite Rose de Fer Ouro Preto, Brésil (6x3,6 cm) …   Wikipédia en Français

  • hématite — [ ematit ] n. f. • 1558; ematite XIIe; lat. hæmatites, mot gr. ♦ Minér. Oxyde de fer naturel de couleur rougeâtre ou brune. Hématite rouge (⇒ ferret) . Hématite hydratée. ⇒ limonite. ♢ Pierre noire, d éclat métallique, formée de cet oxyde. Bague… …   Encyclopédie Universelle

  • Hematite — Hématite Hématite Général Nom IUPAC trioxyde de difer, Oxyde de fer rouge, Oxyde de fer jaune No CAS …   Wikipédia en Français

  • Hematite — Hem a*tite, n. [L. haematites, Gr. ? bloodlike, fr. a i^ma, a i matos, blood.] (Min.) An important ore of iron, the sesquioxide, so called because of the red color of the powder. It occurs in splendent rhombohedral crystals, and in massive and… …   The Collaborative International Dictionary of English

  • hematite — 1540s, haematites, from M.Fr. hematite (16c.), from L. haematites, from Gk. haimatites lithos bloodlike stone, from haima (gen. haimatos) blood (see EMIA (Cf. emia)). Earlier as emachite (late 14c.) …   Etymology dictionary

  • hematite — [hem′ə tīt΄, hē′mətīt΄] n. [L haematites < Gr haimatitēs, lit., bloodlike, red iron ore < haima, blood: see HEMO ] a reddish brown to black, rhombohedral mineral, Fe2O3, that is a major ore of iron; ferric oxide: see RED OCHER hematitic… …   English World dictionary

  • hematite — hematitic /hee meuh tit ik, hem euh /, adj. /hee meuh tuyt , hem euh /, n. a very common mineral, iron oxide, Fe2O3, occurring in steel gray to black crystals and in red earthy masses: the principal ore of iron. [1535 45; < L haematites… …   Universalium

  • hématite — (é ma ti t ) s. f. Minerai de fer qui est un peroxyde de ce métal.    Hématite brune, nom donné à l hydroxyde de fer.    Adj. Pierre hématite. HISTORIQUE    XVIe s. •   Terre scellée, bol fin, pierre haematiste, coral, PARÉ XVIII, 66. ÉTYMOLOGIE… …   Dictionnaire de la Langue Française d'Émile Littré

  • hematite, US — hematitas statusas T sritis chemija apibrėžtis Mineralas. formulė Fe₂O₃ atitikmenys: angl. haematite, GB; hematite, US; red hematite; red iron ore rus. гематит; железный блеск; красный железняк …   Chemijos terminų aiškinamasis žodynas

  • HÉMATITE — s. f. Sanguine, mine de fer d un rouge brun. On dit aussi adjectivement, Pierre hématite …   Dictionnaire de l'Academie Francaise, 7eme edition (1835)


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