1 Corundum – Gems stone
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Blue sapphire gemstone Specimen

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Category Archives: Corundum

Spinel

SPINEL

 

 

COLOUR : Red,pink,blue to mauve

 

COMPOSITION :MgAI2O4

CRYSTAL STRUCTURE :cubic

HARDNESS :8specific gravity :3.6

LUSTER:Vitreous

TRANSPARENCY :  Transparent to translucent

METAPHYSICA:Calm,loyalty, stress reliefmeditation,crisis aversion,strength,self-healing ,purpose

OTHER:Very high melting point of 2135 Celsius

Spinel is found in a wide range of colours due to the presence of various impurities ,and is transparent to almost opaque .Red spinel coloured by  chromium and iron is the most popular ,although for many years it was thought  to be a variety of ruby .The orange –yellow or orange-red variety is called rubicelle (a diminutive of the French  word for ruby ).Blue spinel is coloured by iron,and less commonly by cobalt .Occasionally, inclusions of crystals such as magnetite or apatite may occur ,and some Srilankan spinel may include zircon crystals surrounded by brown haloes .Star stones are rare ,but when cut encabochon may show 4-rayed or 6 rayed stars.

OCCURRENCE : Spinel occurs in granites and metamorphic rocks,  and is often found in association with corundum .Octahedral crystals and waterworn pebbles in a wide range of colours are found in the gem gravels of Burma ,Srilanka,and Madagascar .Other localities include Afghanistan ,Pakistan, Brazil Australia ,Sweden ,Italy ,Turkey ,the former USSR,and the USA.

REMARK :Synthetic spinel has been manufactured since 1910 .It has been used to imitate diamond ,or coloured to imitate stone such as aquamarine and zircon .Blue synthetic spinel ,coloured by cobalt ,has been used to imitate sapphire .The name may derive from the Latin word spina, meaning little thorn referring little thorn ,reffering to the sharp points on some crystals .

COLOURLESS SAPPHIRE

COLOURLESS SAPPHIRE

The different colours found within members of the corundum group are due to small amounts of metal oxide impurities .Corundum without impurities  is rare,but found is classified as colourless sapphire .Stones made up of different colours,  including colourless areas ,are more common .Stones like these are generally orientated by the cutter so that the colour is at the base. Then ,when viewed from above ,colour fills the stone.

OCCURENCDE : Truly colourless sapphire is found in Srilanka  .Cloudy or milky coloured  sapphire is also found in Srilanka ,and referred to locally as geuda .Heat treatment of geuda produces blue sapphire ,much of which is faceted and used in jewellery .Some Srilankan  corundum  shows red, blue, and colourless areas,which may be faceted or polished to give an interesting stone.

REMARK:  Synthetic colourless corundum has been produced by the Verneuil method since about the 1920s, and has been called diamondite .

 

GREEN SAPPHIRE

From medieval  times until the end of the 19th  century green sapphire was reffered to as “oriental peridot “ .Many sapphires that appear green actually consist of very fine alternating bands of blue and yellow sapphire,which may be visible under a microscope .

OCCURRENCE: Green sapphires are found in Thailand ,Srilanka ,and Australia .

PINK SAPPHIRE

Pure pink sapphire is coloured by very small quantities of chromium ,and with increasing amount of chromium .Tiny amount of iron may produce pink-orange stones called padparadscha ,or iron and titanium impurities togather make a purplish stone. Pink sapphires are often cut with a deep profile .

OCCURRENCE : Pink sapphires ,from a very pale and delicate pink to a near –red ,occur in Srilanka ,Burma,and East Africa .

REMARK: Like rubuies pink sapphires are believed to ward  off ill –health and misfortune .For the wearer to gain benefit of the stone ,however ,it is thought necessary for it to be worn directly on the skin. Therefore stones are cut so that ,when set in a piece of jewellery ,the back makes contact with the skin .

 

YELLOW SAPPHIRE

Up until the end of the 19th century yellow sapphire was known as “oriental topaz” (only blue corundum was called sapphire ). Nevertheless yellow and greenish yellow sapphires make unusual and attractive gemstones in their own right .

OCCURRENCE: In Queensland and New south wales (Australia) ,a greenish  yellow purely yellow stones in Srilanka ,Montana (USA),and East Africa.