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Encyclopedia > Spinel
Spinel

General
Category Mineral
Chemical formula MgAl2O4
Identification
Color Various, red to blue to mauve. Dark green, brown. Black
Crystal habit Cubic, octahedral
Crystal system Isometric
Cleavage Indistinct
Fracture Conchoidal, uneven
Mohs Scale hardness 8.0
Luster Vitreous
Refractive index 1.712-1.762
Pleochroism Absent
Streak White
Specific gravity 3.54-3.63

The spinels are any of a class of minerals which crystallize in the isometric system with an octahedral habit. The general formula is as (X)(Y)2O4, with X representing cations occupying tetrahedral sites and Y cations occupying octahedral sites. Divalent, trivalent, and quadrivalent cations can occupy the X and Y sites, and they include magnesium, zinc, iron, manganese, aluminium, chromium, titanium, and silicon. Image File history File linksMetadata Download high-resolution version (1673x1254, 538 KB) Spinel. ... Minerals are natural compounds formed through geological processes. ... This article does not cite its references or sources. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete class of point groups. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... For fractures in geologic formations, see Rock fracture. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... The streak (also called powder color) of a mineral is the color of the powder produced when it is dragged across a unweathered surface. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Minerals are natural compounds formed through geological processes. ... Quartz crystal Synthetic bismuth crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules... In crystallography, the cubic crystal system (or isometric crystal system) is the most symmetric of the 7 crystal systems. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... An ion is an atom or group of atoms with a net electric charge. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Standard atomic weight 26. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... General Name, Symbol, Number titanium, Ti, 22 Chemical series transition metals Group, Period, Block 4, 4, d Appearance silvery metallic Standard atomic weight 47. ... It has been suggested that Silicons ranking be merged into this article or section. ...


The oxygen anions are arranged in a cubic close-packed structure. In the normal spinel structure, X cations occupy the tetrahedral sites, and Y the octahedral sites. For inverse spinels, half the Y cations occupy the tetrahedral sites, and both X and Y cations occupy the octahedral sites.


Important members of the spinel group include:

True spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones of Myanmar and Thailand. Gahnite, ZnAl2O4, is a rare mineral belonging to the spinel group. ... Spinel is one of a group of minerals which crystallize in the isometric system with an octahedral habit, and whose chemical compositions are analogous. ... Chromite, iron magnesium chromium oxide: (Fe,Mg)Cr2O4, is an oxide mineral belonging to the spinel group. ... // Headline text Magnetite is a ferrimagnetic mineral form of iron(II,III) oxide, with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Emery (also known as iron spinel and hercynite) is a common impure variety of the mineral corundum. ... Ulvöspinel or ulvospinel is an iron titanium oxide mineral with formula: Fe2TiO4. ... Jacobsite is a manganese iron oxide mineral. ... Trevorite is a very rare nickeliferous variety of spinel. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. ... Earth cutaway from core to exosphere. ... A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. ... This article or section does not cite any references or sources. ...


Spinel usually occurs in isometric crystals, octahedrons, usually twinned. It has an imperfect octahedral cleavage and a conchoidal fracture. Its hardness is 8, its specific gravity is 3.5-4.1 and it is transparent to opaque with a vitreous to dull lustre. It may be colorless, but is usually various shades of red, blue, green, yellow, brown or black. There is a unique natural white spinel, now lost, that surfaced briefly in what is now Sri Lanka. Another famous spinel is the Black Prince's Ruby in the British Crown Jewels. This article or section does not cite any references or sources. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625–750 nm. ... YOU SUCK!!!!! ... Mossy, green fountain in Wattens, Austria. ... A yellow Tulip. ... Brown, when used as a general term, is a color which is a dark orange, red or rose, of very low intensity. ... Black cat, thought by some to cause bad luck (see superstition) Black is the shade of objects that do not reflect light in any part of the visible spectrum. ... The Black Princes Ruby set in the Maltese cross in the front of the Imperial State Crown of England. ... Coronation Chair and Regalia of England The collective term Crown Jewels denotes the regalia and vestments worn by the sovereign of the United Kingdom during the coronation ceremony and at various other state functions. ...


The transparent red spinels are called spinel-rubies or balas-rubies and were often confused with actual rubies in ancient times. "Balas" is derived from Balascia, the ancient name for Badakhshan, a region in central Asia situated in the upper valley of the Kokcha river, one of the principal tributaries of the Oxus river. Yellow spinel is called rubicelle and violet-colored manganese-bearing spinel is called almandine. Ruby is a red gemstone. ... Badakhshan is a region comprising parts of northeastern Afghanistan and of Tajikistan. ... World map showing the location of Asia. ... The Amu Darya (in Persian آمودریا; Darya means river in Persian) rises in the Pamirs and flows mainly north-west through the Hindu Kush, Turkmenistan, and Uzbekistan to join the Aral Sea in a large river delta. ...


Spinel is found as a metamorphic mineral, and also as a primary mineral in basic rocks, because in such magmas the absence of alkalis prevents the formation of feldspars and any aluminium oxide present will form corundum or combine with magnesia to form spinel. This is why spinel and ruby are often found together. Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ... In chemistry, an alkali (from Arabic: al-qalyالقلوي, القالي ) is a basic, ionic salt of an alkali metal or alkali earth metal element. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. ... Ruby is a red gemstone. ...


Spinel, (Mg,Fe)(Al,Cr)2O4, is common in peridotite in the uppermost Earth's mantle, between the Mohorovicic discontinuity (the Moho) and a depth of 70 kilometers or so; below that depth, the spinel (if present) becomes increasingly rich in chromium, as with increasing depth, pyrope-rich garnet becomes the more stable aluminous mineral in peridotite. At depths significantly shallower than the Moho, calcic plagioclase is the more stable aluminous mineral in peridotite. Peridotite xenolith from San Carlos, southwestern United States. ... Earth cutaway from core to exosphere. ... Mohorovičić discontinuity. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... The pyrope is a garnet. ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ...


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