Chromite was opened in 1845. The name of this crystal comes from the presence in it chemical composition chrome. It should be noted that it contains Fe oxide. Clusters of this crystal, depending on the origin, contain accessors of Mg and Al, Ti, Zn, sometimes the presence of Mn is observed.
The crystal is related to a group of red stones - spinels.
Chromite deposits and mining in India, South Africa, the Philippines, Turkey, Zimbabwe, Finland, Cuba, Albania, Kazakhstan.
V Russian Federation clusters of this crystal are on Urals, Yakutia.
Chemical and physical properties of chromite
The mineral is similar to magnetite. However, it has no magnetic properties. The finest chromite particles are translucent with a brownish tint.
By hardness - 5.5;
by density - from 4.5 to 4.8, 4.2.
Cleavage is absent. The crystal is fragile and heavy.
Mineral of dark brown color, even turning black. Chromite shines with a metallic or semi-metallic light.
Chemical formula: FeCr2O4.
It contains 32% FeO and 68% Cr2O3
The system is cubic.
The fracture is uneven. Molecular Weight - 223.9
IMA status was first described in 1959.
Chromite is a common mineral. It happened in a magmatic manner. Serpentine, chrysolite - satellites of the stone; in rare cases - emerald-colored garnet and рlatina.
Crystals are resistant to weathering. In hot countries, at high temperatures, they are prone to oxidation and destruction.
Application of chromite
Ferrochrome is used in metallurgy. For anti-corrosion coating of products, chromium is used. It is also used for the production of paints that are resistant to weathering. In the leather industry, the mineral also has a role to play. Poor quality ores are used for preparation fireclay bricks designed for facing work.
Chromite, its medicinal properties
Healers and other experts traditional medicine in rare cases such a crystal is used. Does it have chromite medicinal qualities are not fully understood. Therefore, discussions are underway about its benefits and use.
Some lithotherapists have noticed that the stone makes the patient feel better with colds. The crystal does not have tremendous healing power, it does not show any special effect on recovery. It only reduces the painful sensations of a person to the signs of a specific disease.
The crystal will give the opportunity to gain the strength to show interest in work even during illness, give energy and optimistic faith in recovery. But it is precisely this circumstance that scares doctors: it can harm health and interfere with a person's recovery.
Chromite, its magical properties
Currently, astrologers and magicians have studied little magical. Some magicians have suggested that the stone can have a twofold effect on the owner.
For example, a person under the auspices of this stone can be successful in work, and lonely and unhappy in personal affairs.
Such events can occur due to the fact that chromite has little strength and takes energy from a person, which then throws it back to the owner, but only to one point, not endowing the rest of the life spheres. Therefore, mediums do not advise using the stone in practical magic, since it does more harm than good.
Astrologers have not yet determined which of the zodiac signs this crystal is patronizing. Chromite- the talisman of powerful magicians. Only in their hands will the stone work in the right direction, take Cosmic energy and give it to its owner. It is noticed that he will resist, because he loves to rest more and it is at this time that he can harm a person.
Chromite is a mineral used industrially as a source of chromium. Alloying steel, the basic metal of modern technology, requires the introduction of chromium into the alloy. Certain types of stainless steel, smelted with the addition of chromium, end up in jewelry workshops. One of the main consumers of chromium - and, accordingly, ore chromite - is the defense industry. The armor plates of military equipment contain chrome!
From the history of the mineral chromite
Various chromium compounds are a very popular material both in today's industry and among artisans of a bygone era. An acute deficiency of chromium was felt in Russia in the 18th century. The discovery of a chromium-containing mineral the next year after the extraction of metallic chromium from the Urals was a significant victory for the then Russian science.The opening took place through the works of Peter Ivanovich Meder, at that time a teacher at the St. Petersburg Mining School. Analyzing the finds made earlier on the banks of the Ural River Vyazga, PI Meder discovered a dense, dimly gleaming mineral with a characteristic metallic luster. When interacting with laboratory reagents, the mineral produced, among other things, chromic acid.
Considering the nondescript stone to be a natural chromium ore, Meder called the mineral "Eisenchrome", that is, chromium iron ore. It happened in 1798. Half a century later, in 1845, Wilhelm Haidinger renamed eisenchrom to chromite. The name stuck.
Chromite properties
Chromite is a dark, dense, lustrous mineral of medium (5 points according to Mohs) or high (up to 7.5) hardness. Chromite color - brown, black; in a thin layer, chromite can shine through with a muted red color, although more often the mineral does not transmit light at all. 
In a chemical aspect chromite is ferrous chromium oxide with the formula FeCr2O4. It is a compound of ferrous oxide FeO and chromium green Cr2O3. In terrestrial nature, pure chromite is practically not found, however, pure chromite is sometimes found in metallic ones. Together with magnesiochromite MgCr2O4, it is included in the isomorphic series of Cr-spinels (Fe, Mg) (Cr, Al, Fe) 2O4.
Separate crystals of chromite - small, black, poorly formed or severely damaged octahedra - are rarely found. More often, chromite appears to the observer in the form of a dense grain that has grown into the accompanying rock. Chromite crystals have a subdued metallic luster.
Use of chromite
In mining, it is customary to call chromites rocks, most of the composition of which falls on Cr-spinels, a, and pyroxene occupy no more than 10% of the mass of the stone. Chromite itself, magnesiochromite, alumochromite Fe (Cr, Al) 2O4, and chromium pikotite (Mg, Fe) (Cr, Al) 2O4 contain a considerable amount of oxidized chromium - from 14% to 62% - and are considered chrome ore. 
Crystalline chromite is not used in the jewelry industry, but chrome garnets, sometimes found in ores, are delivered to cutting workshops without delay. Contains chromite rocks and some metals
The mineral belongs to the class of oxides and is an iron oxide with chromium. It is sometimes called chromium iron ore. The chromite stone has the studied properties, meaning, but does not affect the various signs of the zodiac.
Chemical formula FeO Cr2O3.
Chromite can be found naturally in the form of continuous granular masses or blotches. In rare cases, chromite occurs in the form of placers. The color range of most specimens is iron black or brown. By outward appearance chromite is confused with magnetic iron ore. But the former has a brown color, and the samples are weakly magnetic. Chromite belongs to the distant relatives of spinel, the chrome spinel group. It includes 20 stones and their varieties.
To date, a pure mineral without various impurities is contained only in meteorite samples. Usually, different elements are found in its composition. The stone is resistant to acids.
| Description | Characteristic |
|---|---|
| Typical impurities | Mg, Mn, Zn, Al, Ti |
| Molecular weight | 223.84 |
| Line color | Brown |
| Shine | Metal |
| Hardness | 10.01.1900 |
| Microhardness | VHN100 = 1278 - 1456 kg / mm2 |
| Break | Uneven |
| Strength | Fragile |
| A type | Isotropic |
| Maximum birefringence | δ = 0.000 - isotropic, does not have birefringence |
| Cell parameters | a = 8.344Å |
| Syngonia | Cubic |
| Unit cell volume | V 580.93 ų |
Origin
It can be safely argued that the stone is of magmatic origin and is formed with platinum during the cooling and solidification of magma during tectonic processes. It can be found in clusters, veins in ultrabasic igneous strata and placers. Platinum, dolomite, talc are often companions of the mineral.
Field
Russia is the world supplier of chromium. There are also deposits in Kazakhstan, South Africa, Turkey and the Philippines.
Story
For the first time a stone was discovered on the territory South Urals... This event was captured by P. Meder in 1799. The description of the mineral took place in 1845 by the Austrian mineralogist Wilhelm von Haidinger.
In old villages, the local population calls the stone "bath" and uses it for its intended purpose. In the process of research, chromite, which is found in stones, has a non-toxic form. Even when heated, various harmful elements are not released into the air from them, therefore it is ideal for baths and saunas. Due to its high melting point, Chromite does not crack due to temperature fluctuations.
Practical use
- The main purpose of the stone is to be used as an ore. Low-grade specimens are suitable for making refractory bricks. This is the first material for metallurgy.
- Also, the stone is part of anti-corrosion coatings. This element increases the hardness of steel, therefore it is used in military affairs.
- It is known in the chemical industry to create artificial bones or joints.
- During temperature exposure in a vacuum environment, chromium is actively combined with carbohydrate, resulting in the formation of hard carbides, which is important for coating diamonds that are used in the metalworking industry. Diamonds processed in this way do not wear out.
- Chromites created under artificial conditions are actively used in electronic technology.
- In jewelry, chromite is also a welcome guest. It creates a beautiful tandem when paired with silver or other light metal. Considering the fact that the color of the mineral is black, there is a chance to look gloomy. Since olden times, jewelry with this stone has been worn by men. Beautiful rings and cufflinks are still part of the fashionable image of young people today.
Therapeutic effect
Modern lithotherapists work little with this stone, because its effect on human body little studied. But in general, its energy helps to cope with colds. In particular, they give the body endurance and strength to continue doing the usual things during an illness.
Magical influence
This aspect has not been fully explored either. It both attracts luck and destroys family bonds... Therefore, it is not suitable as a talisman.
It does not affect the zodiac signs either. Chromite is a stone, the energy of which can only be controlled by strong magicians.
Chromite (chromium iron ore) is an ore mineral that belongs to the group of oxides. In its composition, the main share is chrome, which is why it received the corresponding name. The stone was scientifically substantiated in 1845 by the Austrian geologist V. Gaidinger. In Russia, it was first discovered in 1799 on the lands of the Southern Urals by P. Meder. In 1957, during geological exploration work, chromite deposits were noticed in the Murmansk region.
The stone has a dark brown tone, often turning into black colors with a metallic sheen. The main elements in its chemical composition are chromium (up to 68%) and iron (up to 32%). Impurities of manganese, magnesium, aluminum, zinc and titanium are often present. Pure chromite is found only in meteorites.
Chromite refers to dense, fragile and heavy stones with an uneven fracture and lack of cleavage. It is of magmatic origin, often adjacent to, and platinum in the rock. It does not lend itself to weathering, and in hot climates, under the influence of high temperatures, it can oxidize and degrade. Chromite does not dissolve in acids.
The mineral is non-toxic when heated to high temperatures, which allows it to be used in baths and saunas. Due to its high refractoriness and heat resistance, it does not crack when heated.
Chromite deposits
Significant deposits of the mineral are concentrated in Russia (Yakutia, the eastern regions of the Urals, the Murmansk region and Altai) and Kazakhstan (Aktobe region). Chromite is also mined in the deposits of India, Turkey, Zimbabwe, the islands of Cuba, Albania, southern regions of Africa, Cuba, the Philippines and Finland.
The magical properties of the mineral
Chromite has a powerful energy that only a strong-minded person can cope with. The stone does not like to work and when you turn to it for help, it randomly produces a message. Therefore, to an unenlightened person, he is able to simultaneously help and bring misfortune. For example, by setting business activities, it can have a negative impact on privacy, dooming its owner to loneliness.
It is forbidden for people with weak willpower and spirit to use the magical properties of chromite, otherwise its energy will negatively affect health.
It is advisable to use this mineral to energize amulets and talismans made of other stones.
Horoscope compatibility
The properties of chromite are not fully understood by astrologers. As a talisman or amulet, it is recommended to strong magicians who will be able to cope with its power.
- The stone is most favorable to the representatives of the Earth element (Taurus, Capricorn and Virgo). With the help of this stone, they can enhance their positive character traits, achieve rapid career growth.
- To the signs of the Water element (Pisces, Scorpions and Cancers) chromite will help to understand the meaning and purpose in life. An amulet in the form of a ring with this stone will indicate to its owner the mistakes he has made and prevent new ones, contribute to material wealth and the fulfillment of desires.
- Representatives of the elements of Fire (Leo, Aries and Sagittarius) can count on the help of the stone in re-educating themselves. The mineral will strengthen their self-confidence, and also help to improve their health.
- The signs of the elements of Air (Aquarius, Gemini and Libra) with the help of chromite will be able to restrain their emotions, they will lose interest in intrigues. The stone will give them peace of mind and balance, which will positively affect their health.
Medicinal properties
Until recently, there was a misconception that a large amount of chromium in the composition of the stone can harm human health. For this reason, traditional healers rarely and with caution used it to treat ailments. However, mineralogical studies dispelled misconceptions, proving that chromium in the mineral does not have toxic properties, does not interact with water and under the influence of high temperatures hazardous substances does not highlight.
Lithotherapists attribute to chromite the healing properties inherent in black stones. It promotes rapid recovery from colds and recovery from hypothermia. It is an effective prophylactic agent for people prone to diseases of the respiratory system and joints. The magnetic properties of chromite are also useful to humans.
The properties of the mineral help to overcome nervous disorders accompanied by sleep disturbances, apathy, obsessive thoughts and panic attacks. To do this, they put him on a pillow at night. Chromite is recommended to be worn by people who have suffered fatal events and have lost faith in themselves because of this. In the early days, the effect of the stone can be so strong that a person can sleep constantly.
To achieve the maximum healing effect, the stone is used for laying sauna stoves. The heated chromite and the properties of the sauna will not only restore the health of the afflicted person in a short time, but will also be useful to a healthy person as a preventive measure. The positive effect of chromite baths on reproductive functions has been proven. Thanks to these qualities, the stone has long been called "heroic".
Application of chromite
The mineral is the main ore of chromium and is widely used in metallurgy. Refractories made of chromite are used for the lining of furnaces for smelting steel. Ferrochrome is used in the production of alloys. To give metal products anti-corrosion properties, they are coated with a special chromium compound. This process is called chrome plating. Chromium is also used in leatherwork and as a filler for resistant enamels in the chemical industry.
In the medical industry, chromite is used for the manufacture of bone and joint implants.
Chromite stones are used for laying stoves in baths and saunas. This is facilitated by its physical properties - resistance to high temperatures, high density and heat resistance. Stones long time retain their structure, do not crack under the influence of temperatures and have a positive healing effect on the human body.
The mineral is quite popular with jewelers. Interesting color of the stone, ease of processing and low price allow it to be used in almost all types of jewelry. The most common chromite jewelry is men's rings and cufflinks. The stone is framed mainly in white metals - silver, white gold or platinum.
Stone price
Chromite is affordable. Its price depends on the purity and quality of the stone, its size and the work of the master.
Untreated chromite, intended for laying baths and saunas, costs between $ 15-20 per 10 kg.
The price of a mineral pendant set in cupronickel is $ 57.
A 2.5 x 4 cm chromite crystal with uvarovite and guianaite costs 32 $.
5 / 5 ( 3 voices)
Chalcedony - many-sided mysterious stone Agate - properties of stone Onyx - a stone of energy and strength Argillite - a favorite stone of the Hyde Indians 
Pyrolusite - black magnesia stone
The composition of chrome spinels (chromeshshelids), like other spinels, is unstable and the identification of individual representatives is conditional. In practice, all chrome spinels are commonly referred to as chromite.
In nature, the most common:
magnochromite (Mg, Fe) Cr 2 O 4
chromopicotite (Mg, Fe) (Cr, Al) 2 O 4
alumochromite Fe (Cr, Al) 2 O 4.
Chromium spinel with the composition FeCr 2 O 4 (actually chromite) was found only in meteorites.
Boldyrev (1935) also proposed to distinguish between:
magnoferrichromite - magnoferrichromite (Mg, Fe) (Cr, Fe) 2 O 4
ferrichromspinel - ferrichromspinel Mg (Cr, Al, Fe) 2 O 4
ferrichrompicotite - ferrichrompicotite (Mg, Fe) (Cr, Al, Fe) 2 O 4.
All chrome spinels by outward signs very similar to each other and practically indistinguishable without chemical analysis.
Synonyms:
Synonyms of magnochromite: birch - beresovite (Simpson, 1922), berezovskite - beresovskite (Simpson, 1932), magnesian and ferruginous chromites (Sokolov, 1948).
Synonyms of chromopikotite: chrome-ceylonite - chrome-ceylonite (Dana, 1892), picrochromite - picrochromite (Simpson, 1920), alumoberezovite - alumoberesovite (Vakhromeev, 1935), alumochromicotite - alumochrompicotite (Vakhromeevy, 1948) , magnesian and ferruginous alumochrompikotites (Sokolov, 1948), magnesian and ferruginous chromnicotites (Sokolov, 1948), chrompleonaste (Vinchel, 1951).
Cobaltchrompicotite - cobaltchrompicotite (Boldyrev, 1935) - contains Co.
Synonyms of alumochromite: hercynitechromite - hercynitechromite (Vakhromeev, 1935), ferrochrompicotite - ferrochrompicotite (Sokolov, 1948).
Synonyms for chromite: chromium iron ore - Chromeisenstein, siderochrome - siderochrome (Yuo, 1841), chromoferrite - chromoferrite (Chapman, 1843), ferrochromite - ferrochromite (Khintse, 1933).
Synonyms for magnoferrichromite: ferrichromite - ferrichromite (Sokolov, 1948), magnesian and ferruginous ferrichromites (Pavlov, 1949), ferroferrichromite - ferroferrichromite (Sokolov, 1948).
Synonyms for ferrichromopicotite: ferrialumochromite and ferruginous ferrialuminochromite (Sokolov, 1948), partly ferroferrialumochromite (Pavlov, 1949).
Irite - irite (Herman, 1841) - turned out to be a mixture of chromite with osmous iridium and other minerals (Dana, 1892), prasochrome (Landerer, 1850) - altered chromite.
origin of name
Names chromite- chromite (Haidinger, 1845), chromicotite - chrompicotite (Petersen, 1869), magnochromite - magnochromite (Bock, 1868), alumochromite - alumochromite and others (Boldyrev, 1935) are given by composition.
For the extreme magnesian member of the series, not established in nature, the following names have been proposed: magnesiochromite - magnesiochromite (Dana, 1892), mitchellite - mitchellite (Prat, 1899), picrochromite - picrochromite (Dana, 1944).
Chemical composition
Chemical theoretical composition:
magnochromite (with Mg: Fe = 1: 1): MgO - 9.69; FeO 17.26; Cr 2 O 3 - 73.05;
chromopicotite (with Mg: Fe and Cr: Al = 1: 1): MgO - 11.01; FeO 19.62; Al 2 O 3 - 27.85; Cr 2 O 3 - 41.52;
aluminochromite (at Cr: Al = 1: 1): FeO - 36.14; Al 2 O 3 - 25.64; Cr 2 O 3 - 38.22;
chromite: FeO - 32.09; Cr 2 O 3 - 67.91.
At high temperatures, chromite forms a solid solution with ilmenite. A number of solid solutions were obtained under artificial conditions between chromite and magnetite, between chromite and magnesioferrite. Under natural conditions, the miscibility of chromite and magnetite is not complete. Miscibility with γ -Al 2 O 3 is allowed.
The presence of solid solutions of ulvöspinel in chromite from Norilsk picrite gabbro-dolerites is assumed. A wide range of isomorphic substitutions is established among bivalent (Mg, Fe, Zn) and trivalent (Cr, Al, Fe) elements. The content of Mg, Fe, Al and Cr can vary considerably. The content of Fe 2 O 3 is usually 3-4, rarely reaches 5-10 and even less often 10-22 mol. %. In the Transvaal chromites, the amount of V ranges from 0.05 to 0.81%. The ZnO content reaches 5.8%. Ni, Mn, Zr, Co, Ti, V are found in small amounts. In chrome spinels, as the Fe 3+ content increases, the Fe 2+ content increases and the Mg content decreases. For chromites from the Stillwater intrusive complex (Montana, USA), a direct dependence of the content of MnO 2 and TiO 2 on the content of FeO, as well as V 2 O 3 and Ga 2 O 3 on the amount of Fe 2 O 3 was noted.
There is a relationship between the composition of chrome spinels and the geological conditions of their formation: chrome spinels from dunites are usually distinguished by the highest Cr content and the lowest Al; chrome spinels from lherzolites are characterized by the lowest Cr content and significant Al; chrome spinels from harzburgites and wehrlites have an intermediate composition. Ore-forming chrome spinels contain more Cr and Mg and less Al and Fe 2+ than accessory chrome spinels of the immediate host rocks. The chrome spinels of the Inaglinsky massif (South Yakutia) contain 1 10 -3 - 1.2 10 -2% of the Pt group metals.
Crystallographic characteristic
Syngonia Cubic O 7 h - Fd3m; and 0 depends on the composition. Z = 8.
In chrome spinels, a 0 decreases with an increase in the Al 2 O 3 content (with a decrease in the Cr 2 O 3: Al 2 O 3 ratio) and the MgO content.
At low temperatures, tetragonal symmetry was found for FeCr 2 O 4. At 90 ° K a 0: c 0 = 1: 0.986.
Class Hexoctahedral O h - m3m (3L 4 4L 3 6L 2 9PC).
Crystal structure
Main forms:
a (001) o (111) f (310) m (311) p (221)
d (110) e (210) n (211) µ
(411) q (331)
Form of finding chromite in nature
Crystal Form... Usually crystals are octahedral in appearance.
Doubles are frequent by (111).
Aggregates. Granular masses, sometimes forming spherical precipitates - nodules, also disseminated grains, rarely crystals.
Chromite forms parallel intergrowths with magnetite... In intergrowths with rutile, the needles of the latter are parallel to the chromite or intersect at an angle of 90 °. In intergrowths of chromite with ilmenite, ilmenite plates are located along (111) chromite; in turn, chromite segregations are oriented parallel to (0001) ilmenite. Oriented chromium pikotite inclusions in diamond are noted:
(111) chrompicotite || (111) diamond
chrompicotite || diamond
(111) and chrompicotite || (001) and diamond
Physical properties
Optical
- The color is black, chrompicotite is brownish black.
- The line is brown.
- Metallic to greasy luster.
- Transparency. In thin chips, they are translucent and translucent. Chrompicotites are more translucent than magnochromites.
Mechanical
- Hardness 5.5-7.5.
- The density of magnochromite is 4.2 (calculated for MgCr 2 O 4 - 4.414), chromite 4.5 - 4.8 (calculated for FeCr 2 O 4 - 5.09).
- Cleavage is absent.
- The fracture is uneven.
- Fragile.
Chemical properties
Chromites float by anionic collectors such as carboxylic acids, alkyl sulfates in an acidic environment, and cationic collectors. The most common chromite collectors are oleic acid and insoluble soaps at a pulp pH of 8-10.
Decomposes when fused with KHSO 4. In polished sections, HNO 3, HCl, KCN, FeCl 3, HgCl 2 and KOH are not etched. The structure is revealed by boiling the mineral with KClO 3 + H 2 SO 4 for 30-60 minutes. Thermal etching at 600-650 ° for 5-8 minutes in an oxidizing environment produces hematite.
The pearl of borax or phosphoric salt is greenish-brown when hot, and emerald green when cooled. When fusion with KNO 3, water-soluble K 2 Cr 2 O 4 is formed.
Other properties
Non-magnetic or weakly magnetic, the magnetic value depends on the content of FeO and Fe 2 O 3. The specific magnetic susceptibility of chromopicotite is 24-890 10 -6 cm 3 / g. Curie point of chrome spinel with a 0 = 8.392 A - 90 ° K.
Infrared spectrum of the arts. FeCr 2 O 4 has two well-separated intense bands with maxima at about 617 and 523 cm -1.
Heating behavior. They melt at 1450-2180 °. The higher the content of FeO and Fe 2 O 3, the lower the melting point. With an increase in the content of Cr 2 O 3 and MgO, the melting point increases. When heated, they give an exothermic effect of about 450 ° and an endothermic effect of about 670 °. When heated to 300 °, the formation of hematite was observed, above 500 ° - the formation of Cr 2 O 3; at 800 ° a solid solution of Cr 2 O 3 and Fe 2 O 3 appears, and at 1000 ° - magnetite. According to Goncharov and Prokofieva, the maximum oxidation of iron occurs at 1000 °.
Artificial production of a mineral
Formed when the corresponding oxides are melted in the presence of mineralizers, during the crystallization of silicate melts of the composition of peridotite with a certain excess of MgO and a small content of Al 2 O 3 and Cr 2 O 3; with strong heating Cr 2 O 3 + FeCl 3 in a crucible with cryolite (actually chromite).
Diagnostic signs
The distinctive features of chrome spinels are black color, a brownish line, high hardness, non-magnetic (or very weak magnetic in ferruginous varieties). An association with olivine, rhombic and monoclinic pyroxenes or secondary products from them - serpentine, talc, chlorite, actinolite is characteristic.
In contrast to magnetite similar under a microscope in reflected light, Cr-spinels are not etched with any standard reagent, while magnetite is easily etched with concentrated HCl. In reflected light, magnesioferrite is also very similar to chrome spinels, but does not show internal reflexes.
Origin and location
Chrome spinels are fairly widespread and are associated almost exclusively with ultrabasic igneous rocks. Dunites, harzburgites and lherzolites usually contain accessory chrome spinels and are also host rocks of chromite ores. Accessory chrome spinels are also known in troctolites and some varieties of the olivine-pyroxene gabbro of the Kempirsay massif in Kazakhstan, the Shorzhinsky massif in Armenia, in the kimberlite rocks of the northeastern part of the Siberian platform (Yakutia). They are also found in stone and some iron meteorites. In the form of inclusions in troilite, as well as in intergrowths with olivine, troilite, and schreibersite, Cr-spinel was found in the samples of the Sikhote-Alin iron meteorite, in the silicate part of the Okhanek meteorite.
There are two main ways in which Cr-spinel deposits are formed.
- Segregation in protocrystallization processes of ultrabasic magma. In this case, accessory chrome spinels are formed in ultrabasic rocks, schlieren accumulations and sheet-like deposits of disseminated chromite ores (the result of gravitational differentiation). An example is the fields of the Bushveld complex in South Africa.
- The separation of ultrabasic magma from residual melts is the formation of the main industrial deposits of the Urals and other geosynclinal regions, which are characterized by clearly limited lens-, pillar- and vein-like ore bodies. Ores have a massive or densely disseminated texture. Deposits of this type are found in Albania, Bulgaria, Turkey, West Pakistan, India and a number of other countries. Inclined pillar-like bodies have been installed at the Alapaevskoye, Verblyuzhiegorskoye, Severokempirsayskoye fields of the Urals.
During the metamorphism and redeposition of Cr-spinels due to serpentinization, industrial deposits are not formed. The presence of kemmererite is characteristic of such chromite segregations.
In the form of detrital grains, Cr-spinels are found in marine sedimentary rocks of various ages - sandstones, gravels, conglmerates, etc. (Ural, Caucasus, Balkans).
Alluvial placers are noted among the deposits of the Otava River in the Czech Republic. Coastal-marine placers are known. Deluvial and eluvial accumulations are found, for example, in the Klyuchevskoy massif (Sverdlovsk region) and the Kemgshrsay massif (Kazakhstan).
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Mineral change
Under the influence of hydrothermal solutions, Cr-spinels undergo changes, leading to the oxidation of Fe 2+ to Fe 3+ and the removal of Al and Mg. Chrompicotites are more easily altered than magnochromite. Sometimes magnetite, hematite, and fuchsite develop along chrome spinels.
During the processes of weathering, oxidation of ferrous iron occurs, possibly with partial removal of magnesium; in this case, the chrome spinels are partially destroyed. The formation of limonite on chrome spinels, less often stichtite, was noted.
Practical use
The main mineral for the production of chromium, its compounds and alloys; ores containing more than 40% Cr 2 O 3 are used. Low-grade ores are used to make refractory bricks.
Physical research methods
Ancient methods. They do not melt under the blowpipe.
Crystalloptic properties in thin preparations (thin sections)
In transmitted light, low-chromium spinels are opaque or olive-green and yellowish-green, high-chromium - brownish-orange, brownish-red and brown. Isotropic, n = 2.08 (Nottingham in Pennsylvania, USA, according to Larsen; contains 52.21% Cr 2 O 3); 2.16 (pieces of North Carolina, USA, according to Larsen); n = 2.58 and 3.03 (measured in infrared light for two samples).
According to McGregor, n chrome spinels containing from 35.1 to 53.1% Cr 2 O 3 ranges from 1.815 to 2.110 and increases linearly (like a 0) with an increase in the content of Cr 2 O 3 and a decrease in the content of Al 2 O 3 ...