Spinel
Overview :
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4 Spinel crystallizes in the isometric system; Common crystal forms are octahedra, usually twinned. It has an imperfect octahedral cleavage and a conchoidal fracture.
Because it contains different mineral elements such as magnesium ，Iron，Zinc , Manganese,Chromium..ect, Members of the spinel group include,
Magnesium spinel (usually comes in red,blue ,green,brown,colorless);
Aluminium spinels; Iron spinels（usually comes in black）;Zinc spinel (usually comes in dark green ); Manganese spinel ; Chromium spinels and Others structure spinel.
Synthetic spinel
Synthetic spinel was accidentally found in the middle of the 18th century.A France chemist Called Z. Bareiss found this byproduct when he developed synthetic sappire.But now people can produce as many as 200 kinds of synthetic spinel .And itself as a kind of jewelry put into the market since 1950.
Since spinel contains different mineral element content,so it gets a very rich color ranges such as white , pink ,red , amaranth ,lavender,blue violet,blue ,yellow,brown…ect.So the people can name the spinel as Red spinel,garnet spinel,violet spinel and blue spinel…ect.
The spinel structure
Chemical formula : MgAl2O4
System of crystallization: isometric system
Crystal habit：octahedrons crystals, rhombus dodecahedron,square Combinate form.
Luster: vitreous to dull luster
Transparency:transparent to opaque.
Rfractive index:1.718,(some up to 2.000 when impurities are present ) ,no double rfractions,no pleochroism.
Optical Phenomena: Asterism,aventurescence. Hardness : 8
Specific gravity：3.5-4.1 Density：3.60g/cm3 (more or less)
Occurrence and Deposit area.
Spinel came in being when the rock-magma invade into impure limestone or dolomite then went through hundreds of year metamorphism .Other spinels occurs in magmaticrock of basic rock .The gem quality spinel here means magnalium spinel (beads or block ) ,which are with good transparency and beautiful colors. While other spinel could be used as magnetic materials as they full of the iron element.
The main deposit areas of the spinel are Burma ,Sri Lanka,Cambodia,Tailand as well as China (some famous productions base such as Henan ,Hebei,Fujian,Xinjiang,Yunnan province).
Properties of spinel
The spinel was regard as one of the most beautiful precious stone since its existence in the society.The transparent red spinels were called spinel-rubies or balas-rubies. In the past, before the arrival of modern science, spinels and rubies were equally known as rubies. There is a unique natural white spinel, now lost.
Some spinels are among the most legendary, famous and charming gemstones:
The 'Timur ruby',weighting 361carats, now stored in England Buckinghamshire gallery.
The Black Prince's Ruby in the British Crown Jewels，weighing 170 carats ,were modern times found not ruby but red spinel .
The Samarian Spinel is the largest known spinel in the world, weighing 500 carats (100 g).
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