Ruby

Ruby is the red variety of the mineral corundum (aluminium oxide). Its colour comes from chromium, which also makes ruby glow red under ultraviolet light, and even in daylight this fluorescence can add to the intensity of its colour. The finest rubies are a vivid, slightly purplish red, often called "pigeon's blood". Pink corundum is called pink sapphire in most markets, and the boundary between pink sapphire and ruby is a matter of colour saturation.

Ruby is one of the four traditional precious gemstones and among the most valuable of all gems. It is very hard (9 on the Mohs scale), second only to diamond among commonly used gems, which makes it extremely durable. Many rubies contain fine needle-like inclusions of rutile, known as "silk", and when these are well aligned, a stone cut as a cabochon may show a six-rayed star (star ruby).

The name comes from the Latin "ruber", meaning red. The Mogok Valley in Myanmar (Burma) has been the most famous source for centuries. Today Mozambique is a leading producer, with other important sources including Thailand, Cambodia, Sri Lanka, Madagascar, Tanzania, Afghanistan and Vietnam.

Before modern gemmology, many red stones were mistaken for ruby. The Black Prince's Ruby in the British Imperial State Crown is actually a red spinel. Almost all rubies are heat-treated to improve their colour and clarity, which is accepted in the trade. Lower-quality stones may be filled with lead glass to hide fractures, which makes them much less durable and should always be disclosed. Synthetic ruby has been made since the early 1900s and is chemically identical to natural ruby; the first laser, built in 1960, used a synthetic ruby crystal. Ruby beads are usually opaque, lower-grade material, often dyed or glass-filled.

Ruby at a glance

Caring for ruby

Ruby is very hard (9 on the Mohs scale) and tough, making it ideal for everyday jewellery. Clean untreated or heat-treated rubies with warm soapy water and a soft brush; ultrasonic and steam cleaning are usually safe for these. However, glass-filled, dyed or fracture-filled rubies must only be cleaned with a soft, damp cloth, as heat, chemicals and even lemon juice can damage the filling. Store rubies separately, as they can scratch other gems.

In folklore

The beliefs below are traditional folklore, included for interest. They are not scientifically proven, and nothing here is medical advice.

In ancient India, ruby was called "ratnaraj", the king of precious stones, and was believed to protect its owner from harm and misfortune. Burmese warriors are said to have inserted rubies into their skin to make them invincible in battle. In medieval Europe rubies were thought to bring health, wealth, wisdom and success in love, and to darken in colour as a warning of danger. Ruby is a birthstone for July and the traditional gift for 15th and 40th wedding anniversaries. It is associated with the zodiac signs Leo, Cancer and Scorpio.

Ruby is traditionally regarded as a stone of passion, vitality and courage. Crystal healing lore holds that it energises the body and mind, boosts confidence and motivation, and encourages love and enthusiasm for life. It is also said to protect the wearer and support the heart and circulation. It is linked to the root and heart chakras.

Related stones

Sapphire (all other colours of corundum), pink sapphire, star ruby and ruby in zoisite. Stones that can look similar include red spinel, garnet (pyrope and almandine), rubellite (red tourmaline), red zircon, red glass and synthetic ruby.

For the technically minded

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