Spinel
Spinel (/spɪˈnɛl, ˈspɪnəl/) is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl
2O
4 in the cubic crystal system. Its name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals.
| Spinel | |
|---|---|
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 2O 4 |
| IMA symbol | Spl |
| Strunz classification | 4.BB.05 |
| Crystal system | Cubic |
| Crystal class | Hextetrahedral (43m) H–M symbol: (43m) |
| Space group | F 4 3 m (No. 216) |
| Unit cell | a = 8.0898(9) Å; Z = 8 |
| Identification | |
| Color | Various; red, pink, blue, lavender/violet, dark green, brown, black, colourless |
| Crystal habit | Octahedral or flat triangular plates caused by twinning |
| Twinning | common |
| Cleavage | None |
| Fracture | Conchoidal |
| Mohs scale hardness | 7.5–8.0 |
| 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 properties | Isotropic |
| Refractive index | 1.719 |
| Pleochroism | Absent |
| Solubility | None |
| Other characteristics | Weak to medium magnetic, sometimes fluorescent (red synthetic yes, natural red sometimes) |
| References | |
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