Dictionary:

hematite

  (hē'mə-tīt')

A black or blackish-red to brick-red mineral, essentially Fe₂O₃, the chief ore of iron.

[Middle English emathite, ematites, from Latin haematītēs, from Greek (lithos) haimatītēs, bloodlike (stone), from haima, haimat-, blood.]

The most important ore of iron, with composition α-Fe₂O₃. The crystals are thick tabular, usually flattened parallel to the base, and are frequently platy in habit. Hematite usually occurs as rouge-red earthy masses of finely divided particles. It is the major red-coloring agent in rocks and is a common interstitial cement in sediments. When mixed with quartzite or finely divided quartz, the mixture is called jasper, jaspilite, or taconite. Botryoidal masses are called “kidney ore,” and splinters of these masses are “pencil ore.”

The color is steel gray, blood red in thin fragments, and streak and powder are rouge red; hardness is 6 on Mohs scale and specific gravity is 5.25. The mineral is only weakly magnetic.

Hematite is the most widespread iron mineral. The most important ores are in low-to-medium-grade metamorphic rocks of sedimentary origin. Enormous beds occur in the Great Lakes region of the United States. Hematite also occurs in contact metamorphic and metasomatic deposits, often derived from the oxidation of magnetite and frequently associated with limestones.

Nearly every country in the world mines some hematite ore; the most important occurrences outside of the United States include India, Cuba, China, Chile, north African nations, and Russia. See also Iron metallurgy; Redbeds.

For more information on hematite, visit Britannica.com.

Environment

A common substance of general occurrence. Found in compact and friable sedimentary beds, in lava flows, as a volcanic sublimate, and as an accessory in veins.

A mineral of widely varied appearance, from soft red sludge to black metallic crystals (specular hematite). Thick tabular crystals with rhombohedrons and scalenohedrons sometimes bordering a base. Also thin flat scales, which may be intergrown into "iron roses." Low basal rhombohedrons often merge into a curved surface to make thin lenticular scales. Also in mammillary or reniform radiating growths, sometimes in micaceous black schistlike rocks, and in soft, red earthy masses of "paint ore."

Red or black. Luster earthy or metallic; hardness 1-6Ɖ; specific gravity 4.9-5.3; streak bright to dark red; fracture conchoidal to uneven; cleavage none, but frequent rhombohedral and sometimes basal parting. Specular varieties brittle; excessively thin plates translucent and red; usually even red grains are slightly magnetic.

Iron (ferric) oxide (70.0% Fe, 30.0% O).

Infusible on charcoal, but becomes darker and strongly magnetic. Soluble in concentrated hydrochloric acid.

The red streak is the most important test in distinguishing dark compact varieties of hematite from limonite. The black metallic crystals of specular varieties (specularite) are similarly differentiated from ilmenite and magnetite. The hardness, infusibility, and magnetism after roasting distinguish it from black sulfide and sulfosalt minerals. Behavior under the blowpipe also distinguishes the soft red varieties from cinnabar, cuprite, minium, and the like. There are some flaky hydrous red iron oxides that are often confused with hematite, of which tiny lepidocrocite (FeO[OH]) is the most important.

The most important ore of iron. It occurs in tremendous beds of sedimentary origin, sometimes hardened, metamorphosed, and enriched by subsequent solutions after being laid down. Small black scales have been found around gas vents on lava flows near volcanoes (Vesuvius and Alaska). Massive black beds and scaly schistose hematite rocks are found in metamorphosed sedimentary formations, and hematite crystals may form in rocks of contact metamorphism. Red hematite commonly forms in the soil as the result of weathering of other iron-bearing minerals, and is responsible for the red coloration of many sedimentary rocks. Hematite has formed important secondary ore deposits after iron sulfides (as in Missouri sinkholes). It is also a primary mineral in veins cutting igneous rocks. It has been suggested that at Los Lagos, Chile, there may have been a lava flow that was pure iron oxide, part of which crystallized as hematite, part as magnetite.

The most spectacular large crystals of hematite--flat plates 6 in. (15 cm) or more across--have been found in metamorphosed Brazilian sediments. Many attractively crystallized specimens of rhombohedral habit, often with an iridescent tarnish, come from the island of Elba, Italy. The famous "iron roses" from crystal-lined pockets in the Alps are unmatched elsewhere, but similar examples have been found near Quartzsite, Ariz. Cumberland, England, produces small specular crystals, and the best examples of the interesting fiber-structured reniform knobs--"kidney ore"--of reddish black splintery ore, which is cut as jewelry material ("Alaska diamonds").

For all of its great iron deposits, the U.S. has not produced many spectacular specimens. The Mesabi Range of Minnesota yields only small crystals, and the softer Clinton Red Beds of Alabama have no crystals. The schistose Michigan hematite is brilliant and typical of that occurrence. In its many varieties hematite is one of the commonest minerals we are likely to encounter.

A mineral, Fe₃O₄, composed of oxidized iron that may be the cause of the red color on Mars.

Hematite
General
Category	Oxide mineral
Chemical formula	iron(III) oxide, Fe2O3, α-Fe2O3
Identification
Color	Metallic grey to earthy red
Crystal habit	Tabular to thick crystals
Crystal system	Hexagonal (rhombohedral)
Cleavage	None
Fracture	Uneven to sub-conchoidal
Mohs Scale hardness	5.5 - 6.5
Luster	Metallic to splendent
Refractive index	Opaque
Pleochroism	None
Streak	Bright red to dark red
Specific gravity	4.9 - 5.3
References	[1][2]

Hematite, also spelled hæmatite, 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 as corundum. Hematite and ilmenite form a complete solid solution at temperatures above 950°C.

Hematite (kidney ore) from Michigan (unknown scale)

Hematite is a very common 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.

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. 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.

The name hematite is derived from the Greek word for blood (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.

Rainbow Hematite from Brazil (unknown scale)

Good specimens of hematite come from England, Mexico, Brazil, Australia and the Lake Superior region of the United States and Canada.

Magnetism

Hematite is an antiferromagnetic material below the Morin transition at 260K, and a canted antiferromagnet or weakly ferromagnetic [1] above the Morin transition and below its Néel temperature at 948K, above which it is paramagnetic.

Hematite specimen showing well developed botryoidal structure for which this mineral is well-known. (Unknown scale)

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 (0.002mB). Adding to the surprise was a transition with a decrease in temperature at around 260 K to a phase with no net magnetic moment.^{[citation needed]}

Dzialoshinksi and later Moriya showed 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.^{[citation needed]}

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.^[3] Two other end-members are referred to as protohematite and hydrohematite.

Hematite on Mars

Image mosaic from the Mars Exploration Rover Microscopic Imager shows Hematite spherules partly embedded in rock at the Opportunity landing site. (Scale: image is approximately 5 cm (2 inches) 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 ^[4]. The mineral was seen in abundance at two sites^[5]. on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris ^[6]. Several other sites also showed hematite, e.g., Aureum Chaos ^[7]. 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 Terrra 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 tagged by the science team "blueberries" (a term which is somewhat confusing, since in spectrally-correct color images they are, in fact, silver-grey in color). Analysis indicates that these spherules are apparently concretions formed from a water solution.

Jewelry

Hematite's popularity for in jewelry was at its highest in Europe during the Victorian era. Whilst in the last 50 years it has been popular in North America, especially in the western United States where it is found in jewelry and art created by the Native Americans. Care should be taken in handling hematite items due to the material's susceptibility to damage.

See also

Hematite carving, 5 cm (2 in) long.

• Iron ore
• Iron oxide
• List of minerals
• Wüstite
• Magnetite
• Mineral redox buffer
• Scientific information from the Mars Exploration Rover mission

References

1. ^ http://webmineral.com/data/Hematite.shtml Webmineral data
2. ^ http://www.mindat.org/min-1856.html Mindat mineral data
3. ^ M.-Z. Dang, D.G. Rancourt, J.E. Dutrizac, G. Lamarche, and R. Provencher. Interplay of Surface Conditions, Particle Size, Stoichiometry, Cell Parameters, and Magnetism in Synthetic Hematite-like Materials. Hyperfine Interactions 117 (1998) 271-319.
4. ^ NASA MGS TES Press Release, May 27 1998 "Mars Global Surveyor TES Instrument Identification of Hematite on Mars", available here
5. ^ Bandfield, J.L., Global mineral distributions on Mars, J. Geophys Res., 107, 2002. See: Mars Global Data Sets: Hematite Abundance
6. ^ 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 abstract here
7. ^ 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

• Martite - Mindat w/ location data
• Iron rose - Mindat w/ locations

External links

• Abandoned Mine Research.
• Mars spheres image.
• Mars trench image showing a shiny texture of half-buried spheres (dark line is equipment shadow)
• Florence Mine, Cumbria, UK.

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