The spinel is a Semiprecious stone used in Joaillerie. That of red color was confused a long time with the Rubis. Its principal producer countries are the Sri Lanka and the Myanmar (in the past Burma).

Physical and optical characteristics

• crystalline System: Cubic
• Group of space: $Fd\; \backslash \; bar\; \{3\}\; m$
• Chemical composition: MgAlO (oxide of Magnesium and Aluminum)
• Color: All colors except yellow
• Hardness: 8.0 on the specific scale of Mohs
• Revolved: 3.6
• Index of refraction: 1.71
• Dispersion: 0.020
• Pleochroism: No

The spinels indicate also a group of minerals of general formula (X 2+ ) (Y 3+ ) (O 2 ), where X 2+ is a divalent Cation and Y 3+ a trivalent cation. Among the members of this group, one can note the Magnétite.

The structure of spinels consists of a compact Empilement cubic with centered oxygen faces. The divalent cations occupy the sites with tetrahedral coordination and the cations trivalent the sites with octahedral coordination .

Synthetic spinel

The colorless synthetic spinel is called in the common language “white Saphir”. At summer sold until in the Eighties like imitation of the Diamond. Is now replaced by the Oxyde of zirconium.

Notes and references of the article

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