Rubies are the gemstone variety of red corundum, the same mineral that is sapphire in any other colour. As such, they have a hardness equal to that of sapphires (9) and their resistance to chipping and scratching makes them the ideal choice for use in jewellery. Rubies are one of the most expensive gemstones available today and are mined in Sri Lanka, Myanmar (Burma), Thailand, Vietnam, China, Afghanistan, Kenya and Tanzania.
As with all gemstones, the quality of the cut of a ruby can either enhance or diminish the natural beauty of the stone. Well-cut rubies will appear to possess more vivid colours and better colour saturation when compared to a poorly cut sapphire. As a result, perfectly cut rubies command naturally higher prices than poorly cut rubies. Oval and cushion cuts are the most common shapes of cut rubies. Emerald and heart shaped rubies are not uncommon and premium prices are tend to be levied on round rubies. Cabochon (dome-shaped) cuts are commonly applied to rubies whose clarity is not ideal for polishing.
Examples of the many shapes available when purchasing rubies, clockwise from top left: round cut ruby (side, top and bottom views), square cut ruby, heart shaped ruby, trillion cut ruby, oval cut ruby.
A ruby owes its colour to the presence of chromium in its chemical composition and increased amounts of chromium lead to increased colour intensity. The intensity of the red colour is the primary factor determining the value of a ruby. The saturation, tone and hue of a ruby should all be taken into account when looking for the ideal stone. Saturation is the brightness or vividness of colour in a ruby and tone refers to the lightness or darkness of a ruby.
Rubies tend to be less clean relative to sapphires. As with all gemstones, inclusions in a ruby indicate the authenticity of the stone and may be used to uniquely identify it. Although increased amounts of chromium in a ruby lead to brighter and more intense red colours, it also leads to a decrease in clarity due to the generation of fractures and inclusions within the stone. A flawless (i.e. inclusion-free) ruby is exceptionally rare and as such can command premium prices. Rubies available in jewellery market places tend to be slightly included at the very least.
The majority of rubies on sale today have been subjected to heat treatment to enhance their appearance and colour. This process is permanent and a treated ruby will not diminish in colour, saturation or hue over time. Many rubies are also heated in the presence of a flux which heals their fractures, thus improving their clarity. Untreated rubies are hard to come by and an authentic, untreated ruby may cost 50% more than it's treated equal.