Hematite

Hematite, also spelled as haematite, is the mineral form of iron(III) oxide (Fe2O3), one of several iron oxides. It is the oldest known iron oxide mineral that has ever formed on Earth, and is widespread in rocks and soils.[5] Hematite crystallizes in the rhombohedral lattice 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 (1,740 °F).

Hematite is 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.

Hematite - Titanomagnitite
A microscopic picture of hematite

Huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that can have still standing water or mineral hot springs, such as those in Yellowstone National Park in North America. 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.

Hematite structure
Crystal structure of hematite
Hematite
WLA hmns Hematite
Brazilian trigonal hematite crystal
General
CategoryOxide minerals
Formula
(repeating unit)
iron(III) oxide, Fe2O3, α-Fe2O3[1]
Strunz classification4.CB.05
Dana classification4.3.1.2
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupR3c
Unit cella = 5.038(2) Å;
c = 13.772(12) Å; Z = 6
Identification
ColorMetallic gray, dull to bright red
Crystal habitTabular to thick crystals; micaceous or platy, commonly in rosettes; radiating fibrous, reniform, botryoidal or stalactitic masses, columnar; earthy, granular, oolitic
TwinningPenetration and lamellar
CleavageNone, may show partings on {0001} and {1011}
FractureUneven to sub-conchoidal
TenacityBrittle
Mohs scale hardness5.5–6.5
LusterMetallic to splendent
StreakBright red to dark red
DiaphaneityOpaque
Specific gravity5.26
Density5.3
Optical propertiesUniaxial (-)
Refractive indexnω = 3.150–3.220, nε = 2.870–2.940
Birefringenceδ = 0.280
PleochroismO = brownish red; E = yellowish red
References[2][3][4]

Etymology and history

The name hematite is derived from the Greek word for blood αἷμα haima, due to the red coloration found in some varieties of hematite[5]. The color of hematite lends itself to use as a pigment. The English name of the stone is derived from Middle French: Hématite Pierre, which was imported from Latin: Lapis Hæmatites around the 15th century, 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%.[6] Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite (Fe2O3H2O). The principal use of ochre is for tinting with a permanent color.[6]

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.[7] Hematite residues are also found in graves from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary red chalk mines have been found that are from 5000 BC, belonging to the Linear Pottery culture at the Upper Rhine.[8]

Rich deposits of hematite have been found on the island of Elba that have been mined since the time of the Etruscans.

Magnetism

Hematite is an antiferromagnetic material below the Morin transition at 250 K (−23 °C; −10 °F), 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 magnetic 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.[9][10] The magnetic properties of bulk hematite differ from their nanoscale counterparts. For example, the Morin transition temperature of hematite decreases with a decrease in the particle size. The suppression of this transition has 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 a 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.[11] Two other end-members are referred to as protohematite and hydrohematite.

Enhanced magnetic coercivities for hematite have been achieved by dry-heating a 2-line ferrihydrite precursor prepared from solution. Hematite exhibited temperature-dependent magnetic coercivity values ranging from 289 to 5,027 Oe. The origin of these high coercivity values has been interpreted as a consequence of the subparticle structure induced by the different particle and crystallite size growth rates at increasing annealing temperature. These differences in the growth rates are translated into a progressive development of a subparticle structure at the nanoscale. At lower temperatures (350–600 °C), single particles crystallize however; at higher temperatures (600–1000 °C), the growth of crystalline aggregates with a subparticle structure is favored.[12]

Mine tailings

Hematite is present in the waste tailings of iron mines. A recently developed process, magnetation, uses magnets to glean waste hematite from old mine tailings in Minnesota's vast Mesabi Range iron district.[13] Falu red is a pigment used in traditional Swedish house paints. Originally, it was made from tailings of the Falu mine.[14]

Mars

07-ml-3-soil-mosaic-B019R1 br
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.[15] The mineral was seen in abundance at two sites[16] on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the Aram Chaos site near the Valles Marineris.[17] Several other sites also showed hematite, e.g., Aureum Chaos.[18] 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 sent 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".[19]

Jewellery

Hematite's popularity in jewellery rose in England during the Victorian era, due to its use in mourning jewellery.[20][21] Certain types of hematite or iron oxide-rich clay, especially Armenian bole, have been used in gilding. Hematite is also used in art such as in the creation of intaglio engraved gems. Hematine is a synthetic material sold as magnetic hematite.[22]

Gallery

Hematite-LTH43A

A rare pseudo-scalenohedral crystal habit

Quartz-Hematite-113680

Three gemmy quartz crystals containing bright rust-red inclusions of hematite, on a field of sparkly black specular hematite

Rutile-Hematite-113489

Golden acicular crystals of rutile radiating from a center of platy hematite

Cylinder seal antelope Louvre AM1639

Cypro-Minoan cylinder seal (left) made from hematite with corresponding impression (right), approximately 14th century BC

Hematite-254990

A cluster of parallel-growth, mirror-bright, metallic-gray hematite blades from Brazil

Hematite.bear.660pix

Hematite carving, 5 cm (2 in) long

Hematit 2

Hematite, var. specularite (specular hematite), with fine grain shown

Hematite-rich BIF ventifact

Red hematite from banded iron formation in Wyoming

Hematite on mars

Hematite on Mars as found in form of "blueberries" (named by Nasa)

Hematite streak plate

Streak plate, showing that Hematite consistently leaves a rust-red streak.

See also

References

  1. ^ Dunlop, David J.; Özdemir, Özden (2001). Rock Magnetism: Fundamentals and Frontiers. Cambridge: Cambridge University Press. p. 73. ISBN 9780521000987.
  2. ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.). "Hematite" (PDF). Handbook of Mineralogy. III (Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 978-0962209727. Retrieved December 22, 2018.
  3. ^ "Hematite Mineral Data". WebMineral.com. Retrieved December 22, 2018.
  4. ^ "Hematite". Mindat.org. Retrieved December 22, 2018.
  5. ^ a b Cornell, Rochelle M.; Schwertmann, Udo (1996). The Iron Oxides. Germany: Wiley. pp. 4, 26. ISBN 9783527285761. LCCN 96031931. Retrieved December 22, 2018.
  6. ^ a b "Ochre". Industrial Minerals. Minerals Zone. Archived from the original on November 15, 2016. Retrieved December 22, 2018.
  7. ^ "Researchers find earliest evidence for modern human behavior in South Africa" (Press release). AAAS. ASU News. October 17, 2007. Retrieved December 22, 2018.
  8. ^ Levato, Chiara (2016). "Iron Oxides Prehistoric Mines: A European Overview" (PDF). Anthropologica et Præhistorica. 126: 9–23. Retrieved December 22, 2018.
  9. ^ Dzyaloshinsky, I.E. (1958). "A thermodynamic theory of "weak" ferromagnetism of antiferromagnetics". Journal of Physics and Chemistry of Solids. 4 (4): 241–255. Bibcode:1958JPCS....4..241D. doi:10.1016/0022-3697(58)90076-3.
  10. ^ Moriya, Tôru (1960). "Anisotropic Superexchange Interaction and Weak Ferromagnetism". Physical Reviews Journal. 120 (1): 91. Bibcode:1960PhRv..120...91M. doi:10.1103/PhysRev.120.91.
  11. ^ Dang, M.-Z.; Rancourt, D.G.; Dutrizac, J.E.; Lamarche, G.; Provencher, R. (1998). "Interplay of surface conditions, particle size, stoichiometry, cell parameters, and magnetism in synthetic hematite-like materials". Hyperfine Interactions. 117 (1–4): 271–319. Bibcode:1998HyInt.117..271D. doi:10.1023/A:1012655729417.
  12. ^ Vallina, B.; Rodriguez-Blanco, J.D.; Brown, A.P.; Benning, L.G.; Blanco, J.A. (2014). "Enhanced magnetic coercivity of α-Fe2O3 obtained from carbonated 2-line ferrihydrite". Journal of Nanoparticle Research. 16 (3): 2322. Bibcode:2014JNR....16.2322V. doi:10.1007/s11051-014-2322-5.
  13. ^ Redman, Chris (May 20, 2009). "The next iron rush". Money.cnn.com. Retrieved December 22, 2018.
  14. ^ "Sveriges mest beprövade husfärg" [Sweden's most proven house color] (in Northern Sami). Retrieved December 22, 2018.
  15. ^ "Mars Global Surveyor TES Instrument Identification of Hematite on Mars" (Press release). NASA. May 27, 1998. Archived from the original on May 13, 2007. Retrieved December 22, 2018.
  16. ^ Bandfield, Joshua L. (2002). "Global mineral distributions on Mars" (PDF). Journal of Geophysical Research. 107 (E6): E65042. Bibcode:2002JGRE..107.5042B. doi:10.1029/2001JE001510.
  17. ^ Glotch, Timothy D.; Christensen, Philip R. (2005). "Geologic and mineralogic mapping of Aram Chaos: Evidence for a water-rich history". Journal of Geophysical Research. 110 (E9): E09006. Bibcode:2005JGRE..110.9006G. doi:10.1029/2004JE002389.
  18. ^ Glotch, Timothy D.; Rogers, D.; Christensen, Philip R. (2005). "A Newly Discovered Hematite-Rich Unit in Aureum Chaos: Comparison of Hematite and Associated Units With Those in Aram Chaos" (PDF). Lunar and Planetary Science XXXVI: 2159. Bibcode:2005LPI....36.2159G.
  19. ^ "Hematite". NASA. Retrieved December 22, 2018.
  20. ^ "Black Gemstones, Diamonds and Opals: The Popular New Jewelry Trend". TrueFacet.com. October 23, 2015. Retrieved December 22, 2018.
  21. ^ "(What's the Story) Mourning Jewelry?". Retrieved December 22, 2018.
  22. ^ "Magnetic Hematite". Mindat.org. Retrieved December 22, 2018.

External links

Aram Chaos

Aram Chaos, centered at 2.6°N, 21.5°W, is a heavily eroded impact crater on the planet Mars. It lies at the eastern end of the large canyon Valles Marineris and close to Ares Vallis. Various geological processes have reduced it to a circular area of chaotic terrain. Aram Chaos takes its name from Aram, one of the classical albedo features observed by Giovanni Schiaparelli, who named it after the Biblical land of Aram. Spectroscopic observation from orbit indicates the presence of the mineral hematite, likely a signature of a once aqueous environment.

Aram Chaos measures about 280 kilometers (170 mi) across, and lies in a region called Margaritifer Terra, where many water-carved channels show that floods poured out of the highlands onto the northern lowlands ages ago. It is in the Oxia Palus quadrangle. The Thermal Emission Imaging System (THEMIS) on the orbiter Mars Odyssey found gray crystalline hematite on the floor of Aram. CRISM, the spectroscope on the MRO, found hydrated sulfates, jarosite, and hematite. Hematite is an iron-oxide mineral that can precipitate when ground water circulates through iron-rich rocks, whether at normal temperatures or in hot springs. The floor of Aram contains huge blocks of collapsed, or chaotic, terrain that formed when water or ice was catastrophically removed. Elsewhere on Mars, the release of groundwater produced massive floods that eroded the large channels seen in Ares Vallis and similar outflow valleys. In Aram Chaos, however, the released water stayed mostly within the crater's ramparts, eroding only a small, shallow outlet channel in the eastern wall. Several minerals including hematite sulfate minerals, and water-altered silicates in Aram suggests that a lake probably once existed within the crater. Because forming hematite requires liquid water, which could not long exist without a thick atmosphere, Mars must have had a much thicker atmosphere at some time in the past.

Corundum

Corundum is a crystalline form of aluminium oxide (Al2O3) typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is also a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure. Corundum has two primary gem varieties: ruby and sapphire. Rubies are red due to the presence of chromium, and sapphires exhibit a range of colors depending on what transition metal is present. A rare type of sapphire, padparadscha sapphire, is pink-orange.

The name "corundum" is derived from the Tamil word Kurundam, which in turn derives from the Sanskrit Kuruvinda.Because of corundum's hardness (pure corundum is defined to have 9.0 on the Mohs scale), it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large tools used in machining metals, plastics, and wood. Some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average Mohs hardness of 8.0.

In addition to its hardness, corundum has a density of 4.02 g/cm3 (0.145 lb/cu in), which is unusually high for a transparent mineral composed of the low-atomic mass elements aluminium and oxygen.

Epitaxy

Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate.

The overlayer is called an epitaxial film or epitaxial layer. The term epitaxy comes from the Greek roots epi (ἐπί), meaning "above", and taxis (τάξις), meaning "an ordered manner". It can be translated as "arranging upon". For most technological applications, it is desired that the deposited material form a crystalline overlayer that has one well-defined orientation with respect to the substrate crystal structure (single-domain epitaxy).

Epitaxial films may be grown from gaseous or liquid precursors. Because the substrate acts as a seed crystal, the deposited film may lock into one or more crystallographic orientations with respect to the substrate crystal. If the overlayer either forms a random orientation with respect to the substrate or does not form an ordered overlayer, it is termed non-epitaxial growth. If an epitaxial film is deposited on a substrate of the same composition, the process is called homoepitaxy; otherwise it is called heteroepitaxy.

Hematite, Missouri

Hematite is an unincorporated community in eastern Jefferson County, Missouri, United States. It is located approximately seven miles northeast of De Soto.

Hematite was platted in 1861. The community was named for nearby deposits of hematite. A post office called Hematite has been in operation since 1858.

Hematite, Virginia

Hematite is an unincorporated community in Alleghany County, Virginia, United States.

Hematite Township, Michigan

Hematite Township is a civil township of Iron County in the U.S. state of Michigan. As of the 2000 census, the township population was 352. The township is named for the masses of hematite iron ore in the rocks prevalent in the area.

Horseshoe Bend (Arizona)

Horseshoe Bend is a horseshoe-shaped incised meander of the Colorado River located near the town of Page, Arizona, in the United States.Horseshoe Bend is located 5 miles (8.0 km) downstream from the Glen Canyon Dam and Lake Powell within Glen Canyon National Recreation Area, about 4 miles (6.4 km) southwest of Page.It is accessible via hiking a 1.5-mile (2.4 km) round trip from U.S. Route 89. Horseshoe Bend can be viewed from the steep cliff above.The overlook is 4,200 feet (1,300 m) above sea level, and the Colorado River is at 3,200 feet (980 m) above sea level, making it a 1,000-foot (300 m) drop.The rock walls of Horseshoe Bend contain hematite, platinum, garnet, and other minerals.By 2018 references to the location on social media had caused the number of visitors to increase significantly.

Iani Chaos

Iani Chaos is a region of chaos terrain at the south end of the outflow channel Ares Vallis, of the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars, centered at approximately ~342°E, 2°S. This is the source region of Ares Vallis. The chaotic terrain is widely believed to have formed via the removal of subsurface water or ice, resulting in flooding at the surface, and the formation of Ares Vallis. Within Iani Chaos, deposited stratigraphically above the chaotic terrain, are smooth, low-slope, intermediate-to-light-toned deposits that are rich in a hydrated mineral that is most likely gypsum as well as hematite.

Iron ore

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in colour from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe3O4, 72.4% Fe), hematite (Fe2O3, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H2O), 55% Fe) or siderite (FeCO3, 48.2% Fe).

Ores containing very high quantities of hematite or magnetite (greater than about 60% iron) are known as "natural ore" or "direct shipping ore", meaning they can be fed directly into iron-making blast furnaces. Iron ore is the raw material used to make pig iron, which is one of the main raw materials to make steel—98% of the mined iron ore is used to make steel. Indeed, it has been argued that iron ore is "more integral to the global economy than any other commodity, except perhaps oil".

Ironstone

Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron compound from which iron can be smelted commercially. This term is customarily restricted to hard coarsely banded, nonbanded, and noncherty sedimentary rocks of post-Precambrian age. The Precambrian deposits, which have a different origin, are generally known as banded iron formations. The iron minerals comprising ironstones can consist either of oxides, i.e. limonite, hematite, and magnetite; carbonates, i.e. siderite; silicates, i.e. chamosite; or some combination of these minerals.

Limonite

Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the three principal iron ores, the others being hematite and magnetite, and has been mined for the production of iron since at least 2500 BCE.

Martian spherules

Martian spherules (also known as blueberries due to their blue hue in false-color images released by NASA) are the abundant spherical hematite inclusions discovered by the Mars rover Opportunity at Meridiani Planum on the planet Mars. They are found in situ embedded in a sulfate salt evaporitic matrix, and also loose on the surface.

Meridiani Planum

Meridiani Planum is a plain located 2 degrees south of Mars's equator (centered at 0.2°N 357.5°E / 0.2; 357.5), in the westernmost portion of Terra Meridiani. It hosts a rare occurrence of gray crystalline hematite. On Earth, hematite is often formed in hot springs or in standing pools of water; therefore, many scientists believe that the hematite at Meridiani Planum may be indicative of ancient hot springs or that the environment contained liquid water. The hematite is part of a layered sedimentary rock formation about 200 to 800 meters thick. Other features of Meridiani Planum include volcanic basalt and impact craters.

Meridiani Planum was chosen as the landing site for the spacecraft landings of MER-B and the ExoMars EDM, the flat terrain, low-elevation, and relative lack of rocks and craters have made it favored location. This region also contains Challenger Memorial Station.

Ochre

Ochre (British English) ( OH-kər; from Ancient Greek: ὤχρα, from ὠχρός, ōkhrós, pale) or ocher (American English) is a natural clay earth pigment which is a mixture of ferric oxide and varying amounts of clay and sand. It ranges in colour from yellow to deep orange or brown. It is also the name of the colours produced by this pigment, especially a light brownish-yellow. A variant of ochre containing a large amount of hematite, or dehydrated iron oxide, has a reddish tint known as "red ochre" (or, in some dialects, ruddle).

The word ochre also describes clays colored with iron oxide, derived during the extraction of tin and copper.

Pot of Gold (Mars)

Pot of Gold is the nickname for a knobby, softball-sized rock in Gusev Crater on Mars. During an examination by the Mars Exploration Rover Spirit on June 25, 2004, Hematite was first detected by Spirit, suggesting a watery past on Mars.

Psilomelane

Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese oxide with variable amounts of barium and potassium. Psilomelane is erroneously, and uncommonly, known as black hematite, despite not being related to true hematite, which is an iron oxide.

SS Irish Pine (1919)

Irish Pine was a 5,621 GRT cargo ship which was built in 1919 for the United States Maritime Commission (USMC) and named West Hematite. She was chartered in 1941 by Irish Shipping Ltd and renamed Irish Pine. On 16 November 1942, Irish Pine was torpedoed and sunk by U-608.

Streak (mineralogy)

The streak of a mineral is the color of the powder produced when it is dragged across an un-weathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus an important diagnostic tool in mineral identification. If no streak seems to be made, the mineral's streak is said to be white or colorless. Streak is particularly important as a diagnostic for opaque and colored materials. It is less useful for silicate minerals, most of which have a white streak or are too hard to powder easily.

The apparent color of a mineral can vary widely because of trace impurities or a disturbed macroscopic crystal structure. Small amounts of an impurity that strongly absorbs a particular wavelength can radically change the wavelengths of light that are reflected by the specimen, and thus change the apparent color. However, when the specimen is dragged to produce a streak, it is broken into randomly oriented microscopic crystals, and small impurities do not greatly affect the absorption of light.

The surface across which the mineral is dragged is called a "streak plate", and is generally made of unglazed porcelain tile. In the absence of a streak plate, the unglazed underside of a porcelain bowl or vase or the back of a glazed tile will work. Sometimes a streak is more easily or accurately described by comparing it with the "streak" made by another streak plate.

Because the trail left behind results from the mineral being crushed into powder, a streak can only be made of minerals softer than the streak plate, around 7 on the Mohs scale of mineral hardness. For harder minerals, the color of the powder can be determined by filing or crushing with a hammer a small sample, which is then usually rubbed on a streak plate. Most minerals that are harder have an unhelpful white streak.

Some minerals leave a streak similar to their natural color, such as cinnabar and lazurite. Other minerals leave surprising colors, such as fluorite, which always has a white streak, although it can appear in purple, blue, yellow, or green crystals. Hematite, which is black in appearance, leaves a red streak which accounts for its name, which comes from the Greek word "haima", meaning "blood." Galena, which can be similar in appearance to hematite, is easily distinguished by its gray streak.

Vanadium(III) oxide

Vanadium(III) oxide is the inorganic compound with the formula V2O3. It is a black solid prepared by reduction of V2O5 with hydrogen or carbon monoxide.It is a basic oxide dissolving in acids to give solutions of vanadium(III) complexes. V2O3 has the corundum structure. It is antiferromagnetic with a critical temperature of 160 K. At this temperature there is an abrupt change in conductivity from metallic to insulating.Upon exposure to air it gradually converts into indigo-blue V2O4.In nature it occurs as the rare mineral karelianite.

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