Spinel

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Spinel
Calcite-Spinel-dtn37a.jpg
Small spinel crystal on top of a white calcite from Mogok, Myanmar, measuring 1.5 × 1.1 × 1 cm in size
General
Category
Formula
(repeating unit)
MgAl
2
O
4
Strunz classification 4.BB.05
Crystal system Cubic
Crystal class Hextetrahedral (43m)
H–M symbol: (43m) [1] [2] [3]
Space group F4 3 m (No. 216)
Unit cell a = 8.0898(9) Å; Z = 8
Identification
ColorVarious; red, pink, blue, lavender/violet, dark green, brown, black, colourless
Crystal habit Octehedra or flat triangular plates caused by twinning
Twinning common
Cleavage None
Fracture Conchoidal
Mohs scale hardness7.5–8.0
Luster Vitreous
Streak White
Diaphaneity Transparent to opaque
Specific gravity (Depending on the composition) The rare Zn-rich spinel can be as high as 4.40, otherwise it averages from 3.58 to 3.61.
Optical propertiesIsotropic
Refractive index 1.719
Pleochroism Absent
Solubility None
Other characteristicsWeak to medium magnetic, sometimes fluorescent (red synthetic yes, natural red sometimes)
References [4] [5]

Spinel ( /spɪˈnɛl,ˈspɪn.əl/ ) is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl
2
O
4
in the cubic crystal system. Its name comes from the Latin word spinella, which means spine in reference to its pointed crystals. [4]

Contents

Properties

Cut spinel Spinelgem.JPG
Cut spinel

Spinel crystallizes in the isometric system; common crystal forms are octahedra, usually twinned. It has no true cleavage, but shows an octahedral parting and a conchoidal fracture. [6] Its hardness is 8, its specific gravity is 3.5–4.1, and it is transparent to opaque with a vitreous to dull luster. It may be colorless, but is usually various shades of red, lavender, blue, green, brown, black, or yellow [7] Some spinels are among the most famous gemstones; among them are the Black Prince's Ruby and the "Timur ruby" in the British Crown Jewels, [8] and the "Côte de Bretagne", formerly from the French Crown jewels. [9] The Samarian Spinel is the largest known spinel in the world, weighing 500 carats (100 g). [10]

The transparent red spinels were called spinel-rubies [11] or balas rubies. [12] In the past, before the arrival of modern science, spinels and rubies were equally known as rubies. After the 18th century the word ruby was only used for the red gem variety of the mineral corundum and the word spinel came to be used. [13] "Balas" is derived from Balascia, the ancient name for Badakhshan, a region in central Asia situated in the upper valley of the Panj River, one of the principal tributaries of the Oxus River. However, "Balascia" itself may be derived from Sanskrit bālasūryaka, which translates as "crimson-coloured morning sun". [14] Mines in the Gorno Badakhshan region of Tajikistan constituted for centuries the main source for red and pink spinels. [13]

Occurrence

Geologic occurrence

Spinel is found as a metamorphic mineral in metamorphosed limestones and silica-poor mudstones. [7] It also occurs as a primary mineral in rare mafic igneous rocks; in these igneous rocks, the magmas are relatively deficient in alkalis relative to aluminium, and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel and ruby are often found together. The spinel petrogenesis in mafic magmatic rocks is strongly debated, but certainly results from mafic magma interaction with more evolved magma [15] or rock (e.g. gabbro, troctolite). [16] [17]

Spinel, (Mg,Fe)(Al,Cr)
2
O
4
, is common in peridotite in the uppermost Earth's mantle, between approximately 20 km to approximately 120 km, possibly to lower depths depending on the chromium content. [18] At significantly shallower depths, above the Moho, calcic plagioclase is the more stable aluminous mineral in peridotite while garnet is the stable phase deeper in the mantle below the spinel stability region. [19]

Spinel, (Mg,Fe)Al
2
O
4
, is a common mineral in the Ca-Al-rich inclusions (CAIs) in some chondritic meteorites. [20]

Geographical occurrence

Spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones of the Badakshan Province in modern-day Afghanistan and Tajikistan; and of Mogok in Myanmar. Over the last decades gem quality spinels are found in the marbles of Lục Yên District (Vietnam), Mahenge and Matombo (Tanzania), Tsavo (Kenya) and in the gravels of Tunduru (Tanzania) and Ilakaka (Madagascar). [13] [21]

Since 2000, in several locations around the world, spinels have been discovered with unusual vivid pink or blue colors. Such "glowing" spinels are known from Mogok (Myanmar), [22] Mahenge plateau (Tanzania), Lục Yên District (Vietnam) [23] and some more localities. In 2018 bright blue spinels have been reported also in the southern part of Baffin Island (Canada). [24] The pure blue coloration of spinel is caused by small additions of cobalt. [25]

Synthetic spinel

Synthetic spinel, accidentally produced in the middle of the 19th century, has been described more recently in scientific publications in 2000 and 2004.[ citation needed ] By 2015, transparent spinel was being made in sheets and other shapes through sintering. [26] Synthetic spinel, which looks like glass but has notably higher strength against pressure, can also have applications in military and commercial use. [27]

See also

Related Research Articles

Corundum Oxide mineral

Corundum is a crystalline form of aluminium oxide typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is 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.

In geology, felsic is an adjective describing igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava.

Gemstone Piece of mineral crystal used to make jewelry

A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks and occasionally organic materials that are not minerals are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.

Sapphire Gem variety of corundum

Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al2O3) with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. It is typically blue, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colors; "parti sapphires" show two or more colors. Red corundum stones also occur, but are called rubies not sapphires. Pink-colored corundum may be classified either as ruby or sapphire depending on locale. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5) – sapphires are also used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, and very thin electronic wafers, which are used as the insulating substrates of special-purpose solid-state electronics such as integrated circuits and GaN-based blue LEDs. Sapphire is the birthstone for September and the gem of the 45th anniversary. A sapphire jubilee occurs after 65 years.

Garnet Mineral, semi-precious stone

Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.

Ruby Variety of corundum, mineral, gemstone

A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum. Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond. The word ruby comes from ruber, Latin for red. The color of a ruby is due to the element chromium.

Olivine Magnesium iron silicate solid solution series mineral

The mineral olivine is a magnesium iron silicate with the chemical formula (Mg2+, Fe2+)
2
SiO
4
. It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickly on the surface. For this reason, olivine has been proposed as a good candidate for accelerated weathering to sequester carbon dioxide from the Earth's oceans and atmosphere, as part of climate change mitigation. Olivine also has many other historical uses, such as the gemstone peridot (or chrysolite), as well as industrial applications like metalworking processes.

Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance.

Kimberlite Igneous rock which sometimes contains diamonds

Kimberlite is an igneous rock, which sometimes contains diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat (16.70 g) diamond called the Star of South Africa in 1869 spawned a diamond rush and the digging of the open-pit mine called the Big Hole. Previously, the term kimberlite has been applied to olivine lamproites as Kimberlite II, however this has been in error.

Anorthosite Mafic intrusive igneous rock composed predominantly of plagioclase

Anorthosite is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present.

Magma chamber Accumulation of molten rock within the Earths crust

A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it upwards. If the magma finds a path to the surface, then the result will be a volcanic eruption; consequently, many volcanoes are situated over magma chambers. These chambers are hard to detect deep within the Earth, and therefore most of those known are close to the surface, commonly between 1 km and 10 km down.

Chromite

Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4). A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy.

Peridotite A coarse-grained ultramafic igneous rock

Peridotite ( PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from Earth's mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole.

Eclogite A dense metamorphic rock formed under high pressure

Eclogite is a metamorphic rock formed when mafic igneous rock is subjected to high pressure. Eclogite forms at pressures greater than those typical of the crust of the Earth. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth.

Cordierite

Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18). A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.

Painite

Painite is a very rare borate mineral. It was first found in Myanmar by British mineralogist and gem dealer Arthur C.D. Pain who misidentified it as ruby, until it was discovered as a new gemstone in the 1950s. When it was confirmed as a new mineral species, the mineral was named after him. Due to its rarity, painite can cost in the range of between US$50,000 to $60,000 per carat.

Komatiite Ultramafic mantle-derived volcanic rock

Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% MgO. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.

Cumulate rock

Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group of igneous rocks. Cumulates can be deposited on top of other older cumulates of different composition and colour, typically giving the cumulate rock a layered or banded appearance.

Harzburgite Ultramafic and ultrabasic mantle rock. Found in ophiolites.


Harzburgite, an ultramafic, igneous rock, is a variety of peridotite consisting mostly of the two minerals olivine and low-calcium (Ca) pyroxene (enstatite); it is named for occurrences in the Harz Mountains of Germany. It commonly contains a few percent chromium-rich spinel as an accessory mineral. Garnet-bearing harzburgite is much less common, found most commonly as xenoliths in kimberlite.

Vladyslav Yavorskyy

Vladyslav Yavorskyy is a gemstone dealer and jeweler based in Bali, Indonesia, United States. He is best known as one of the world's largest dealers and authorities on spinel. He is also the author of at least six gemstone-related books, one of which was named as one of the Best Books for Gem Lovers by JCK magazine in 2016

References

  1. Robert John Lancashire. "Normal Spinels". CHEM2101 (C 21J) Inorganic Chemistry – Chemistry of Transition Metal Complexes. University of the West Indies. Archived from the original on 2018-08-08.
  2. N. W. Grimes; et al. (Apr 8, 1983). "New Symmetry and Structure for Spinel". Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences. 386 (1791): 333–345. Bibcode:1983RSPSA.386..333G. doi:10.1098/rspa.1983.0039. JSTOR   2397417. S2CID   96560029.
  3. L. Hwang; et al. (Jul 1973). "On the space group of MgAl
    2
    O
    4
    spinel"
    . Philosophical Magazine . doi:10.1080/14786437308217448.
  4. 1 2 Spinel, Mindat.org
  5. Spinel Mineral Data, WebMineral.com
  6. Nesse, William D. (2000). Introduction to mineralogy. New York: Oxford University Press. pp. 362–363. ISBN   9780195106916.
  7. 1 2 Klein, Cornelis; Hurlbut, Cornelius S., Jr. (1993). Manual of mineralogy : (after James D. Dana) (21st ed.). New York: Wiley. ISBN   047157452X.
  8. Sir Thomas Butler (1989). The Crown Jewels and Coronation Ceremony. Pitkin. p. 6. ISBN   978-0-85372-467-4.
  9. Pardieu, V.; Farkhodova, T. (Summer 2019). "Spinel from Tajikistan". InColor: 30–33. Retrieved 28 April 2021.
  10. "Samarian spinel". Dictionary of Gems and Gemology: 657–737. 2005. doi:10.1007/3-540-27269-0_19.
  11. Lytvynov, L.A. (2011). "On the words used as names for ruby and sapphire" (PDF). Functional Materials. 18 (2): 275. Retrieved 29 April 2021.
  12. Hughes, R.W. (1994). "The rubies and spinels of Afghanistan: A brief history" (PDF). Journal of Gemmology. 24 (4): 256–267. doi:10.15506/JoG.1994.24.4.256 . Retrieved 29 April 2021.
  13. 1 2 3 Pardieu & Farkhodova 2019.
  14. Biswas, A.K. (2001). "Minerals and their Exploitation in Ancient and Pre-modern India". In Ramachandra Rao, P.; Goswami, N.G. (eds.). Metallurgy in India : a retrospective. New Delhi: India International Publisher. pp. 1–22. ASIN   B002A9M6QU.
  15. Irvine TN (1977). "Origin of chromite layers in the Muskox intrusion and other stratiform intrusions: a new perspective". Geology. 5 (5): 273. doi:10.1130/0091-7613(1977)5<273:ooclit>2.0.co;2.
  16. Leuthold J, Blundy JD, Brooker RA (2015). "Experimental petrology constraints on the recycling of mafic cumulate: A focus on Cr-spinel from the Rum Eastern Layered Intrusion, Scotland". Contributions to Mineralogy and Petrology. 170 (2): 12. Bibcode:2015CoMP..170...12L. doi:10.1007/s00410-015-1165-0. hdl: 1983/43578f76-07c8-4676-84d1-d763d5228efb . S2CID   129562202.
  17. O Driscoll B, Emeleus CH, Donaldson CH, Daly JS (2009). "The roles of melt infiltration and cumulate assimilation in the formation of anorthosite and a Cr-spinel seam in the Rum Eastern Layered Intrusion, NW Scotland". Lithos. 111 (1–2): 6–20. Bibcode:2009Litho.111....6O. doi:10.1016/j.lithos.2008.11.011.
  18. Klemme, Stephan (2004). "The influence of Cr on the garnet–spinel transition in the Earth's mantle: Experiments in the system MgO−Cr
    2
    O
    3
    −SiO
    2
    and thermodynamic modelling"
    (PDF). Lithos. 77 (1–4): 639–646. Bibcode:2004Litho..77..639K. doi:10.1016/j.lithos.2004.03.017.
  19. Philpotts, Anthony R.; Ague, Jay J. (2009). Principles of igneous and metamorphic petrology (2nd ed.). Cambridge, UK: Cambridge University Press. p. 17. ISBN   9780521880060.
  20. MacPherson, G.J. (2007). "Calcium–Aluminum-Rich Inclusions in Chondritic Meteorites". Treatise on Geochemistry: 1–47. doi:10.1016/B0-08-043751-6/01065-3. ISBN   9780080437514.
  21. Pardieu, Vincent; Hughes, R. W.; Boehm, E. (2008). "Spinel: Resurrection of a classic". InColor Magazine: 10–18. Retrieved 29 April 2021.
  22. Pardieu, Vincent (2014). "Hunting for "Jedi" Spinels in Mogok". Gems & Gemology. 50 (1).
  23. Wondermondo (16 June 2019). "Finds of cobalt blue spinel in Lục Yên, Vietnam".
  24. Mining.Com (5 April 2019). "Scientists figure out origin of cobalt-blue spinel in Canada's Arctic".
  25. Boris Chauviré, Benjamin Rondeau, Emmanuel Fritsch, Phillipe Ressigeac, and Jean-Luc Devidal (Spring 2015). "Blue Spinel From the Luc Yen District of Vientam". Gems & Gemology.CS1 maint: multiple names: authors list (link)
  26. "Researchers finding applications for tough spinel ceramic". Phys.org. 24 April 2015.
  27. "Transparent Armor from NRL; Spinel Could Also Ruggedize Your Smart Phone". Naval Research Laboratory. 23 April 2015.

Bibliography