The Sapphire (Corundum) is, along with the Ruby, the Diamond and the Emerald one of the 4 precious stones. Its blue varies from the palest sky to the deep blue of Eastern nights.
Etymologically, for some, the name « Sapphire » was translated from the Greek sappheiros : blue; or from the Hebrew sappir significant « the most beautiful thing ». This would in particular justify the name blue Sapphire, yellow Sapphire, pink Sapphire, green Sapphire, white Sapphire.
Afterwards, only the blue variety was named Sapphire.
History, deposits and extraction of Sapphires
At the end of the 18th century, it was discovered that the Sapphire (just like the Ruby) was a precious stone from the group of corundum. The legend tells that the Sapphire protected one from desire and that it was a gem of the soul.
The blue Sapphire, less rare than the Ruby has a magmatic origin. The mother rock is granite, pegmatite or basalt.
Industrial deposits of Sapphire are located in Australia, Sri Lanka (Ceylon), Thailand and Myanmar (formerly Burma). There are some in India (Kashmir) as well and the USA (Montana).
The Australian mines of Queensland have been known since 1870. The mother rock is basalt. Sapphires are harvested from eluvium through washing.
They have a very irregular quality : the stones have a deep blue which look like green-tinted blue or even black at times under artificial light. There are also Black Star Sapphires.
The mines of New South Wales have produced Sapphires of beautiful colours since 1918.
Myanmar (formerly Burma)
There are also alluvial deposits in northern Burma, close to Mogok, which produce sapphires, Rubies and Spinels. The mother rock is pegmatite. It’s in this region that in 1966 the biggest Star Sapphire in the world was found, weighing in at 63,000 carats (12.6kg).
In Sri Lanka (Ceylon), the Sapphires have been extracted since Antiquity. Like Rubies, the deposits are located in the region of Ratnapura in the south-western part of the Island. The Sapphires come from alluvial deposits, called « illam » in the country’s language. They are extracted from the rocks and the sands of the bottom of flowing waters. The mother rock is « dolomitized » limestone incorporated in gneiss (type of granite).
The extracted stones are usually forget-me-not blue with a mauve tint. There are also yellow kinds, orange (padparadscha), green, pink, brown, colourless (or white).
In Thailand (Siam), the two big Sapphire mines are Bang-Khacha, close to Chanthabury, South East of Bangkok and Bo-Ploi, northwest of Bangkok. The mother stone is basalt and they are alluvial and eluvium deposits.
Blue Sapphires are dark and they lean towards green-blue.
The State of Kashmir in India produces the best Sapphires in terms of colour and quality.
The mother rock is a vein of highly kaolinised crystalline layers.
The deposits are more than 5,000 metres high in altitude in the region of Zanskar, southeast of Srinagar. They are eluvium deposits and the extracted Sapphires are deep blue with a silky glint.
The mines have been exploited since 1870 and have a low output which explains why these Sapphires have almost disappeared from the market and that they are by far the rarest and most prized ones.
The first Sapphire deposits in Montana, USA were found in 1894. The mother rock is an andesite vein. There are two kinds of extraction techniques : excavation of the mother rock or washing alluvial deposits.
The colour of the extracted Sapphires varies from pale blue to steel blue.
Various Sapphire deposits in the world
Other deposits are exploited in the world : in Brazil (state of Matto Grosso), in the western part of Cambodia, in Kenya, Malaysia, Rhodesia, Madagascar and Tanzania.
Among the most famous stones are :
- The Star of India Star, 563 carats, the biggest Cut Star Sapphire ;
- Midnight Star, 116 carats, Black Star Sapphire.
These two exceptional stones belong to the American Museum of Natural History in New York.
The Ruspoli, 135.80 carats, diamond-shaped belonged to Louis XIV and is currently being exhibited at the Museum of Natural History in Paris.
Finally, the Talisman of Charlemagne is remarkable ; it belongs to the treasury of the Cathedral of Reims, France.
Colour and properties of Sapphires
Like the Ruby, colour alone is not enough to determine the origin of the Sapphire.
The beauty of a Sapphire results from the combination of its criteria of colour, intensity and homogeneity.
Iron and titanium ions give the Sapphire its blue colour. The presence of vanadium gives the stones a purple tint. A smaller proportion of iron is responsible for yellow and green tints. The chrome ions give the stone its pink colour. But the most prized colour is pure blue.
Its hardness is similar to that of the Ruby (index 9 on MOHS’ 10-degree scale).
This hardness varies depending on the directional axis of the stone. This criterion has importance for the cut of the gem.
Its colour is usually an intense and mellow deep sea blue. Some Burmese Sapphires have an amazing sky blue and their transparency is slightly hazy which gives the gem its mellow aspect.
There are “silk” type inclusions (mass of Rutile needles). When the Sapphires have a nice colour and cut in cabochon, they reach a very high value because of the beauty of the star that can be seen ; they are thus named « Star Sapphire Cabochon ».
Sapphires of Siam (Thailand)
The blue of these Sapphires is more or less bright and some have the ultramarine of Burmese Sapphires. Others have a much more green-tinted blue which makes them resemble Australian Sapphires.
They can sometimes display an alternation between coloured and colourless strips which form partial chevrons or hexagons.
The Ceylon Sapphire, the blue of which is mostly due to titanium oxide, sometimes has mauve tints which are accentuated in the presence of artificial light. This comes from a certain proportion of chrome oxide which is at the origin of the colour Rubies.
Particularities of Ceylon Sapphires
The Sapphires cut on site have uneven shapes, asymmetrical and ovoid type (rounded on one side and almost sharp on the other). The pavilion covered with facets is never centred. This cut technique is used so as to highlight the Sapphire’s colour and to make up for inadequacies and imperfections. This way, some Sapphires which seem to have a uniform and sweet-looking blue owe this only to a colour touch placed at the centre of the tip of the culet.
Even rarer, the Top-Colour Sapphires are almost colourless in all their mass and only a thin blue layer on the table and the crown make it look deep blue.
The disadvantage of these Sapphires is that when seen from the sides, they’re colourless. The risk is that they might be mistaken for doublets (assembled stone resulting from gluing a part of a natural and coloured stones to a piece of colourless crystal or quartz).
These Sapphires give an impression of magnificence and smoothness.
The blue of these Sapphires is special : it’s a cornflower blue, bright and wonderfully mellow.
The coloration seems to spread in the areas that are more or less mellow because of the very small fibrous feather-shaped inclusions.
The light green in other Sapphires is turquoise in the Kashmir Sapphire.
Their colour varies from average blue to very dark blue (some stones look like black onyx) but still mixed with green and yellow-green.
These Sapphires have the biggest proportion of iron which is responsible for their green tones.
The structure and the inclusions are similar to that of the Ceylon Sapphires : presence of colour straight strips or polygonal with very different intensities.
When cut in cabochon, they make nice dark Star Sapphires whose asterism effect has 6 and sometimes 12 pointed stars.
Pailin Sapphires (Cambodia)
These Sapphires have a very nice and bright mid-range blue, close to Ceylon Sapphires, a bit less mauve-tinted and brighter than Burmese Sapphires. The distribution of colour is done in strips or chevrons, similar to most Sapphires.
Usually, Sapphires are cut in their country of origin. This cut is not always satisfactory because the lapidaries prefer keeping the stone at its maximum weight.
As a consequence, many stones need to be re-cut afterwards to be optimised in jewellery.
The step cut and the fancy cut (pear, cushion, heart, and marquise) maintain the stone’s transparency and brilliance. The least transparent stones are often cut in cabochon.