The Corundum Group

Rubies and sapphires are part of the corundum group. On the Mohs scale of hardness they are 9. The jump in hardness between corundum and diamond is much more than it seems from the scale. A diamond is 140 times as hard as corundum, but corundum is very hard wearing… seven times as hard as topaz. Corundum can be cut either en cabouchon or faceted.

The red corundum is called ruby, from the Greek name for red – rubeus. There is no demarcation between ruby and sapphire – they are the same chemical composition but the colour pigment influencing ruby is chrome. The most sought-after colour is “pigeon blood” red – pure red with a slight blue hue. The names “Burmese’ or ‘Siam Ruby” refer to colour and not to origin. Large rubies are very rare. Good colour rubies are one of the most expensive gems. Large rubies are rare and therefore more expensive than comparable size diamonds. Rubies are hard but brittle, so care must be taken when setting and cutting.
Large rubies are very rare. Good colour rubies are one of the most expensive gems. Large rubies are rare and therefore more expensive than comparable size diamonds. Rubies are hard but brittle, so care must be taken when setting and cutting.
Imitation rubies have been on the market since the beginning of the 1900s. They have the same chemical composition but are man-made or manufactured, their most common name being “reco-rubies” meaning reconstituted rubies. The easiest way to detect a genuine from a synthetic gem, is from the natural inclusions found in a natural ruby when the crystal grows. Many people see inclusions in stones and think that this de-values the stone. On the contrary, this would be a sure way to tell that they are genuine as opposed to synthetic. Synthetic gems appear “too good to be true” with no flaws.
