Non-silicates

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Spinel #1 PPL

Spinel thin section

Apparently from the Latin spinella (= little thorn), in allusion to the spine-shaped octahedral crystals. Formula: MgAl2O4 System: Cubic (Isometric) Color: Black, blue, red, violet Lustre: Vitreous Hardness: 7½–8 Density:...