When we think of sapphires, thanks to popular culture, what comes to mind is a gorgeous blue heart-shaped gemstone that the old lady threw into the ocean at the end of ‘Titanic’; the film (more about that necklace in another post).
Corundum is the oxide mineral that gives rise to the ruby and the sapphire, which is said to naturally occur in other colours as well; that is due to trace elements of other metals. The hardness of this precious stone measures 9 on the Mohs scale.
Where colour is concerned, sapphires are most popular as blue stones and colour plays a significantly large role when determining the value of the gem. Greater the intensity of the colour; all the more great is its value. Strongly saturated (vivid brightness) sapphires in medium tones that aren’t too dark command the highest prices in the gem market.
(Geologic Occurrence of Corundum; image courtesy of Geology.com)
Pink sapphires belong to the “fancy” sapphire coloured category and are known among the circles of gem traders as padparadscha, whose colour lies somewhere between salmon to orange. These fancy sapphires fetch a high price in the market especially in comparison to other fancy sapphires (sapphires of other colours).
Coloured sapphires range from hues of lemon, peach, orange and red to olive green and colourless (also known as white) sapphires.
(This 15.6 ct zircon displays an obvious pleochroic “bow tie” effect. Photo courtesy of Gia.edu by Joel Arem.)
Where clarity is concerned, inclusions occur in sapphires too but not to the extent that they occur in rubies. Some of these inclusions are needle thin and intersect each other are known as silk, while others can form colour bands or the shape similar to fingerprints. These inclusions can cause the price of the gem to drop or soar depending on the effect they have on its clarity. The star effect, for instance, is called asterism and can hike up the price of the stone if the star is well-defined. Pleochroism is the phenomenon that occurs when the faceted stone shows off a different colour when looked at from a different direction. This is also quite an important characteristic of a sapphire.
More on sapphires in the next post!