The Corundum Family and Sapphires

Classification

Any gem-quality stone within the corundum family is generally called sapphire, except red (ruby) and pink-orange (padparadscha). They share similar characteristics, being the hardest stones after diamonds.  In fact, corundum is so hard it is often used in industry for abrasive and cutting purposes, like emery paper and drills. Rubies and sapphires are also used in lasers: in 1960 the very first laser was invented and a ruby was used to create the laser beam.

Origins and Varieties

Sapphires are mostly found in Sri Lanka, formerly Ceylon and these are often a lovely distinctive cornflower blue shade although they also come from Madagascar, Burma, Thailand and Tanzania (among others).

Colour Saturation and Rarity

Despite the fact that people generally think of blue sapphires in engagement rings, there is a wide range of types and colours, but they also share the same refractive index so can be identified easily by a gemologist. Deeply saturated blue sapphires are valued, but over-saturation may lower a gemstone’s value. The deep blue shade is the most popular for engagement rings however at Harriet Kelsall Bespoke Jewellery we love to use sapphires of differing shades. If a sapphire is to be called blue it must not have less than 15% secondary colour tones (eg. yellow or pink) within its structure. Any more than this and it becomes something along the lines of ‘greenish-blue’ or ‘violet’ which are then called ‘fancy colours’.  The blue colour comes from titanium, and too much of this in a stone makes it look almost black, which reduces its value.

White Sapphires

At the other end of the scale, clear, white sapphires are the purest form of corundum because they contain none of the trace elements which cause colouration. Pure, white sapphires are rare, and pink sapphires gained popularity after deposits were discovered in Madagascar in the 1990s. They are a good alternative to diamonds for your engagement ring if you want a clear stone because they are so tough and sparkly. Having said that, large stones are not that widely available because it’s not easy to find that purity in nature. Stones with colourless areas are more common, and these are generally cut so that the colour is at the base. This means that when it’s viewed from above, colour fills the stone. This often gives interesting variations when viewed at different angles and getting this to look good takes a skilled stone cutter.

Pink, Orange, Yellow, and Green Sapphires

Pink Sapphires

Pink sapphires have become more widely available since the 1990s when new deposits were found in Madagascar. Until then, they were exceptionally rare, and found only occasionally in Vietnam, Sri Lanka and Burma, but because of the new availability, their popularity has shot up in engagement rings. They come in a full colour range of the palest pink through to fuchsia, and all colours seem to be equally popular. The colour comes from traces of chromium.

Orange and Yellow Sapphires

Yellow sapphires also come in a wide range of colours and tones from light canary through to a deep golden. Until the end of the century, it was not known that sapphires were anything other than blue. As a result, they were known as oriental topaz up until that point. Naturally occurring orange sapphires are rarely seen however heat treated stones are more widely available.

Green Sapphires

Green sapphires vary between light lime green and olive in colour. Many actually consist of very fine bands of blue and yellow, which can be seen under a microscope, but blend if looked at with the naked eye. This was once known as oriental peridot. We love green sapphires here at Harriet Kelsall Jewellery Design as the green is a gentle natural green – not a harsh green – which particularly suits paler skin tones and eyes. Also green sapphires change in different lights and at different angles if well cut.

Rare varieties and Phenomenon Stones

Lavender, Violet Sapphires

Lavender and violet sapphires, while rare, can resemble tanzanite although more durable and highly sought after for their beauty. They can be quite expensive in larger sizes if they are of a good quality. Despite their rarity, we are able to source them for customers and they are well worth it!

Star Sapphires

Star sapphires and rubies are classified as a ‘phenomenon’ stone. They are likely to have contributed to the legend and lore concerning the powers of the sapphire because the very first sapphires cut would have been shaped in a cabochon form and when the stars appeared no one could explain them!

We now know that star sapphires have to be cabochon cut to allow the 6 pointed star to be created within the sapphire, which happens because of the way a single point of light reflects from the internal structure of the stone. This structure is made up of microscopic needles which cross at different angles and with the correct angle of light entering the stone, bounces off the needles and accentuates the appearance of the star. This phenomenon is called ‘asterism’. They come in a wide variety of colours, although the most prevalent are a greyish white or greyish blue.

Strangely for such a fabulous stone, most rough star sapphires are sent directly to high temperature ovens to melt the silk-like needles and destroy the star effect. This is because they are worth more as classically faceted sapphires. Heat treated star sapphires do exist but are hard to make because the intense heat needed in this process damages the needles that produce the star.

Heat-Treated and Colour-Changing Sapphires

Colour changing sapphires are also classified a ‘phenomenon’ stone. Many people do not believe they exist until they see them in real life. Generally, in fluorescent lighting these stones look blue and in incandescent light they look purple, although they also come in red/brown, green/red, and green/yellowy green. A ring with one of these stones set in it can look like two different rings depending upon the time of day! A stone with a complete colour change (e.g. red/green) is more expensive than one with a more subtle change. Rough star sapphires are often heat-treated to remove the star effect and increase their value.

Padparadscha Sapphires

Padparadscha is the only variety of corundum other than ruby that is not simply known as a colour of sapphire. Its name is an ancient Sanskrit word which describes the colour of the lotus flower – a pinky orange colour. Padparadscha is extremely rare, and as such, very expensive, particularly for a fine piece. Similarly coloured stones are not classified Padparadschas if they have any hint of reddish orange or brown in them, although these too are stunning stones.

Sapphire Symbolism & Birthstone

Sapphires are the birthstone of September and the astrological stone of Leo. The various colours are thought to protect the wearer from all sorts of evil, illness, stress and general harm, and as such, a lovely choice for your engagement ring!