If the diamond is the queen of the gemstones, corundum is her consort. A red corundum is known as a ruby, and while sapphires are mostly associated with a particular deep blue colour, all non-red corundums are sapphires.

While one can easily say that a green or yellow corundum is a sapphire, there is a significant grey area when it comes to reddish pink or pinkish red stones. Are they rubies or are they sapphires? In the grand scheme of things, this doesn’t matter, but everything else being equal, a blood-red ruby will usually fetch a better price than a cerise coloured sapphire.

Being the same mineral, rubies and sapphires have the same physical attributes. They are very tough, with a hardness of 9 on Mohs scale. This makes them great choices for jewellery, especially rings, and along with diamonds and emeralds, they’re considered true gemstones.

Varieties

While all corundums are either rubies or sapphires, there are several sub-groups within these categories. These are:

Star sapphires and star rubies

Due to what is known as asterism (aster being Latin for “star”), some opaque sapphires and rubies will show a star when cut en cabochon. The star will move around a bit depending on how the light hits the stone, and a good, clear star can be quite fetching when set in jewellery. A good quality star ruby (or sapphire) will have the star centred at the middle of the stone, so if you would like to find a piece of jewellery with a fancy star, make sure to take note of where the star is located. Fake star rubies do exist, but they are very easy to tell apart from the real deal.

Padparadscha sapphire

This is a rare variety of sapphire with a pinkish orange colour. I have yet to see it in any antique jewellery online, and it would most likely be way too expensive for Georgina.

Colour-changing sapphire

Some sapphires change colour depending on the colour of the light and will usually be blue in natural light and purple in incandescent light. Note that the quality of the color as well as the amount of change will have a huge impact on the value.

Fake rubies and treated sapphires

All kinds of corundum stones may be treated in order to enhance their appearance, and thus increasing their perceived value. While making synthetic corundum in labs is fairly easy today, inferior stones have been improved on for centuries, and other, less expensive minerals have been passed off as the real deal.