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Spinel is found as a metamorphic mineral in metamorphosed limestones and silica-poor mudstones. [9] 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 ...
The mineral ceylonite has the chemical composition of (Mg, Fe 2+) Al 2 O 4, putting it into a group of minerals known as the spinel group, or the oxide spinels. The oxide spinels have a formula of the model [A][B] 2 O 4; where [A] is commonly Fe 2+, Mg 2+, or Mn 2+, and [B] is Fe 3+, Al 3+, or Cr 3+. It is an iron-rich variety of the spinel ...
There are many more compounds with a spinel structure, e.g. the thiospinels and selenospinels, that can be synthesized in the lab or in some cases occur as minerals. The heterogeneity of spinel group members varies based on composition with ferrous and magnesium based members varying greatly as in solid solution, which requires similarly sized ...
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]
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
Ulvöspinel or ulvite is an iron titanium oxide mineral with formula: Fe 2 Ti O 4 or TiFe 2+ 2 O 4. It forms brown to black metallic isometric crystals with a Mohs hardness of 5.5 to 6. It belongs to the spinel group of minerals, as does magnetite, Fe 3 O 4.
Gahnite, ZnAl 2 O 4, is a rare mineral belonging to the spinel group. It forms octahedral crystals which may be green, blue, yellow, brown or grey. It often forms as an alteration product of sphalerite in altered massive sulphide deposits such as at Broken Hill, Australia.
Common, naturally occurring ferrites (typically members of the spinel group) include those with nickel (NiFe 2 O 4) which occurs as the mineral trevorite, magnesium containing magnesioferrite (MgFe 2 O 4), [7] [8] cobalt (cobalt ferrite), [9] or manganese (MnFe 2 O 4) which occurs naturally as the mineral jacobsite.