Ranging from the deepest midnight to brilliant cornflower blue, sapphires have long been prized for their intense, velvety colour.

In the trade, “blue sapphire” refers to stones ranging from very light to very dark greenish or violetish blue, as well as those in various shades of pure blue. Large, top-quality stones are rare, but blue sapphires in other sizes and grades are almost always available.

The calming influence of blue has also made it an enduring symbol for loyalty and trust- one reason that women around the world choose sapphire for their engagement rings.

Not all sapphires are blue however, fancy sapphires, as they are called come in violet, green, yellow, orange, pink, purple and intermediate hues. There are also parti-coloured sapphires that show a combination of different colours.

Sapphire is the US birthstone for September.