Ruby is one of the four recognized precious gemstones along with emerald, sapphire and diamond. Being the birthstone of July, it is one of the highest valued coloured gems admired since history began.
Ruby Origin and Formation
The English name “ruby” comes from the Latin word “ruber” and “rubeus”, meaning red. In the ancient Indian language of Sanskrit, ruby is called “ratnaraj”, which translates as “king of precious stones”. Interestingly, in ancient times before technological advancement, all red gemstones were considered rubies including spinel, garnet and tourmaline.
Rubies are formed under immense pressure and intense heat under the earth’s surface for millions of years. They consist of oxygen atoms called corundum and aluminium which turn into liquid under heat and pressure and seep into cracks in igneous or metamorphic rocks.
When the liquid cools it usually turns into colourless crystals. However, when minuscule traces of other minerals mix with corundum they turn it into reds, pinks, blues and yellows.
If the microelement is chromium then the corundum turns red and we get rubies. In the case of iron and titanium, we get blue sapphires.
Colour is the most important quality factor of rubies. To figure out which ruby colour is the best, we need to consider three components – hue, tonal grade and saturation.
Hue describes the type of red, meaning how red is the gemstone and if there are any signs of other colours such as blue, brown or yellow. As a rule, the redder the stone, the better.
Tonal grade refers to the level of lightness or darkness of the red. The best rubies have a solid colour that is not too dark and not too light. When the colour of rubies is too light, they are classified as pink sapphires, but the line between pinkish red rubies and pink sapphires is so fine that people can argue for hours over when a ruby stops being ruby and becomes a pink sapphire.
Saturation refers to the intensity of the colour. This characteristic defines if the gem has weak, vivid, strong or intense colouring. The most desirable and sought-after ruby colours are strong pure red and red with a hint of blue which is also known as “pigeon’s blood”, usually sourced in Myanmar (Burma).
It’s worth mentioning that some rubies possess fluorescence, a phenomenon that causes them to glow in ultraviolet light.
Natural rubies typically display inclusions, which are not looked upon as negative attributes as they would be for diamonds, for example. In opposite, these flaws are considered part of the character of rubies and lack of any inclusions is a sign of synthetic stones as the latter tend to be eye-clean.
The value of rubies depends on whether these inclusions are visible to the naked eye and if they affect the gem’s transparency and brilliance. It is recommended to avoid larger inclusions that affect the transparency of the gem.
Inclusions and cracks that reach the surface will affect the durability of the stone and detract from its beauty. Such stones are not desirable as well.
Types of Rubies
As mentioned above rubies are a crystalline form of aluminum oxide which get their red colour by the presence of chromium microelements. However, rubies differ from each other in the range of reds and secondary colour tones which are classified into a few types and named according to their mining area.
Burmese or Myanmar Rubies
Burmese or Myanmar rubies are the most sought-after type. These gems come in vibrant red colour and very few inclusions. However, these top-quality gemstones always have some inclusions which are the sign of their originality.
Thai rubies are exceptional gemstones that occupy the second position just after the Burmese rubies. They come in darker hues with signs of brown and burgundy.
Madagascan rubies are quite new to the market. They come in red with orange and pink tints. Although rubies from Madagascar are new on the scene they are in the top list due to their unique colour combinations.
African rubies usually come in purplish to dark red colour; however, the best colour of African rubies is the fine dark red. Since they are usually heavily included, these gemstones are often cut into cabochon. Transparent gems are cut and polished into faceted stones.
Tanzanian rubies are famous for their exceptional clarity and they are less expensive than the ones from Burma and Thailand.
Rubies from Tanzania are very similar to hessonite due to their beautiful colour; however, the intensity of their colour diminishes with size, meaning smaller Tanzanian rubies are more valuable.
Mozambique produces different types of high-quality rubies but they are noted for their star rubies discovered in Montepuez in the northern part of the country.
Rubies mined in Afghanistan range from light to dark red colour. The main sources are the Badakshan and Jagdalek regions. The Jagdalek rubies come in colours from faint to deep red and have qualities not found elsewhere in the world.
The price of natural rubies is mainly determined by their colour. A high-quality ruby should have a pure vivid red colour, neither too dark nor too light with no obvious colour undertones.
Although blemished in rubies are tolerated, obvious cracks and cloudy appearance will always devalue the stone.
Since ruby is a very expensive precious gemstone, cutters are very careful not to waste any material during the cutting process. This influence the way the gem is cut. Rubies come in all shapes, but round and oval cuts are the most popular because these cuts bring out the red and the sparkle.
As a general rule, cutters try to consider the hue, tone and saturation of the rough to maximize vibrance and minimize the poor parts of the stone. Besides, they have to consider the pleochroic aspect of the stone; rubies can display two colours depending on the angle at which they are viewed. Cutters get the most value from the red being the dominant colour.
Gemstones over 1 carat are very rare and expensive as a result. With an increase in size, the price of a ruby increases dramatically. A 5-carat ruby may cost 25 times the price of a 1-carat gem in case all other characteristics are equal.
|Chemical Name||Aluminium oxide|
|Hardness||9 on the Mohs scale|
|Refractive Index||1.76 - 1.78|
|Specific Gravity||4.0 - 4.1|
|Transparency||Transparent to opaque|
|Fluorescence||Strong - carmine red|