Rubies are the next most expensive stone after diamond and they are nearly as hard measuring a 9 on the Mohs scale. The classic ruby shade to us is that deep, hot pink although they do occur in paler colours too. The most expensive shade of ruby is the wonderfully named "pigeon blood", this is the rarest and like the name suggests, is blood red.

The worlds most expensive coloured gemstone (not a diamond) is the Sunrise ruby. A 25.59ct Burmese "pigeon blood" ruby named after a poem by Rumi.

Synthetic rubies these are produced in a laboratory, they are flawless and consistently hot pink in colour. Synthetic stones are frowned upon in the jewellery world as they are man made but this shade would be impossible to achieve naturally so, for the ruby, we make an exception. The heart cut stone photographed here is a synthetic ruby and the only synthetic stone in the collection.

Glass filled rubies are lower grade stones that have been heated and filled with a  glass to improve the clarity of the stone. These are considered half way between a synthetic and a natural stone, they are "treated". Often still quite opaque and retain the silky natural qualities of the original ruby. They are one-offs and, personally, we quite like them. The teardrop stone photographed is one of Tessa's personal collection.

Colours: Pink to blood red.

Mohs scale: 9

Crystal Formation: Terminated tabular hexagonal prisms

Countries of origin: Burma, Thailand, Cambodia, Afghanistan, Australia, Brazil, Colombia, India, Namibia, Japan, Scotland, Madagascar, Nepal, Pakistan, Tajikistan, Tanzania, and Vietnam.