Besides blue sapphire and ruby, the corundum family also includes so-called “fancy sapphires”. They come in violet, green, yellow, orange, pink, purple and intermediate hues. There are also “parti-colured” sapphires that show combinations of different colours. Some stones exhibit the phenomenon known as colour change, most often going from blue in daylight or fluorescent lighting to purple under incandescent light. Sapphires can even be grey, black or brown.
Fancy sapphires are generally less available than blue ones, and some colours are scarce, especially in very small or very large sizes. Still, fancy sapphires create a rainbow of options for people who like the romance associated with this gem, but who also want something out of the ordinary.
The mineral corundum is composed only of aluminum and oxygen, and it requires a growth environment that’s free of silicon. However, silicon is a very common element, making natural corundum relatively uncommon. In its purest state, corundum is actually colourless. Colourless sapphires were once popular diamond imitations, and they’ve staged a comeback as accent stones in recent years.
But colourless corundum is rare. Most corundum contains colour-causing trace elements. When the trace elements are iron and titanium, the corundum is blue sapphire. Only a few hundredths of a per cent of iron and titanium can cause the colour, and the more iron the corundum contains, the darker the blue. Chromium can cause the red colour of ruby or the pink of pink sapphire.
In the 1990s, discoveries in East Africa and Madagascar brought fancy sapphires widespread recognition. The new sources supplemented production from traditional ones like Sri Lanka and Madagascar and increased the availability of yellows, oranges, pinks and purples.
The colours attracted jewellery designers who wanted to move away from traditional hues of red, blue and green. Now, contemporary designers arrange fancy sapphires in stunning rainbow suites.
Corundum can show a phenomenon called asterism, or the star effect. This phenomenon usually appears as a six-ray star pattern across a cabochon-cut stone’s curved surface. The star effect can be seen in ruby or any colour of sapphire, and it arises from white light reflecting from numerous tiny, oriented needle-like inclusions.
Besides fancy sapphire and star corundum, there’s another interesting variety: colour-change sapphire. These fascinating stones change colour under different lighting. Their presence adds a special dimension to the already amazing corundum family of gems.
Both blue and fancy sapphires come from a variety of exotic sources including Madagascar, Tanzania, Sri Lanka, Myanmar and Australia.