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Inverse spinel structures have a different cation distribution in that all of the A cations and half of the B cations occupy octahedral sites, while the other half of the B cations occupy tetrahedral sites. An example of an inverse spinel is Fe 3 O 4, if the Fe 2+ (A 2+) ions are d 6 high-spin and the Fe 3+ (B 3+) ions are d 5 high-spin.
Hercynite is a spinel of regular symmetry and normal cation distribution, but some disorder occurs in its structure. It consists of ferrous (Fe 2+) ions and aluminium ions (Al 3+); however some ferric ions (Fe 3+) may be located in the structure of hercynite. [5] Melting point of this mineral is inbetween 1,692–1,767 °C (3,078–3,213 °F). [6]
Filipstadite is a very rare mineral [4] of the spinel group, with the formula (Mn,Mg)(Sb 5+ 0.5 Fe 3 + 0.5)O 4. [5] It is isometric, [3] although it was previously thought to be orthorhombic. When compared to a typical spinel, both the octahedral and tetrahedral sites are split due to cation ordering. [3] Filipstadite is chemically close to ...
Ringwoodite is polymorphous with forsterite, Mg 2 SiO 4, and has a spinel structure.Spinel group minerals crystallize in the isometric system with an octahedral habit. Olivine is most abundant in the upper mantle, above about 410 km (250 mi); the olivine polymorphs wadsleyite and ringwoodite are thought to dominate the transition zone of the mantle, a zone present from about 410 to 660 km
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The 3rd analytical group of cations includes ions which form hydroxides that are insoluble even at low concentrations. Cations in the 3rd group are, among others: Fe 2+, Fe 3+, Al 3+, and Cr 3+. The group is determined by making a solution of the salt in water and adding ammonium chloride and ammonium hydroxide. Ammonium chloride is added to ...
The red spheres are X atoms (usually oxygens), the blue spheres are B atoms (a smaller metal cation, such as Ti 4+), and the green spheres are the A atoms (a larger metal cation, such as Ca 2+). Pictured is the undistorted cubic structure; the symmetry is lowered to orthorhombic, tetragonal or trigonal in many perovskites.
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