Ruby

Ruby

July’s birthstone

Colours Red
Family

Corundum. Al203

Hardness

9

Refractive Index

1.76     - 1.78

Specific Gravity

3.97 – 4.05

Crystal System

Trigonal

Enhancements May be enhanced
Major Sources

Thailand, Vietnam, Cambodia, Myanmar, Kenya, India, Tanzania, India

Warnings for Care Colour change occurs at moderate to high heat

Ruby Facts

Ruby and Sapphire are members of the Corundum family. If Corundum exhibits a colour from slightly pinkish red, through red to slightly reddy brown then it is called a Ruby. All other colours of Corundum are termed Sapphires. Corundum is second only to Diamond in terms of its physical hardness, (although exhibiting only  1/140th of the hardness of Diamond), This hardness (9 on the Moh's scale) in relation to all other gemstones has ensured its position with Sapphire and Emerald  as one of the so called "precious gems".

Ruby is named after the Latin word "rubeus" for red. With colour varying from deposit to deposit, depending on the Chromium and Iron content of the stone. The most desirable color is termed  "pigeon’s blood", a pure red with a hint of blue, only currently found in the mines of Myanmar (Burma).

Ruby is one of the most expensive gems available today, with large rubies being considerably rarer than comparable diamonds. The highest price ever paid for a gemstone on auction on a per carat basis was for a Ruby.

Ruby is the birthstone for those who are born in July, and is used in certain cultures to celebrate a couple's 15th and 40th anniversary.

Topics Of Interest:
Ruby - What Causes the Colour
Purchasing Ruby
Mineable Deposits?
Ruby - Common Treatments
Important & Famous Ruby
Ruby - The Legend

Ruby - What Causes the Colour

The Chromium and Iron content of a Ruby determines its colour. Traces of Chromium in the crystal lattice account for the pinkish and red coloured stones, while the addition of iron to the lattice (in addition to the already present Chromium) creates the brown hues. The distribution of color is often uneven, with characteristic strips orientated at 60o and 120o and darker pigmentation spots being common.

Purchasing Ruby

When looking for a Ruby  color is without doubt the most important consideration, with clarity a close second. Buyers need to bear in mind that large clean Rubies are rare and command a hefty premium over included examples.

Colour
The most desirable color is the so-called "pigeon's blood", red, as found in the Mogok Valley, Mong Hsu, and Namya deposits in Myanmar (Burma). This the finest Ruby colour is best described as being a vivid medium-dark toned red with a hint of blue, exhibiting an intense saturation of color.

Lighting
Ruby is another example of a pleochroic stone. In the case of Ruby the stone is dichroic, exhibiting two distinct colours when viewed along either the x or y-axis. Asterism (a 3 or 6 pointed star effect) is common in low transparency example with a high "silk" content and are best  viewed in natural light.

Many rubies exhibit what is termed as ruby-red fluorescence in long or short wave UV, and this property can in some cases be used to help identify a stone's geographic origin. Myanmar (Burmese) rubies often fluoresce so strongly that the effect is noticeable even in sunlight; with the stone literally appearing to glow with an "electric red effect". Thai and Vietnamese rubies generally lack this property.

Clarity
Inclusions are common in ruby and not always an indication of lesser quality. The type of inclusion (mineral, pipe or cavity) can be used to indicate the source area. Needle; inclusions of Rutile cause the "silky shine" or "silk" which imbibes the stone with an almost sleepy appearance. If such a stone is cut in a particular orientation en cabochon it can expose the rare cat's eye effect (Chatoyancy) . Structurally oriented rutile needle inclusions cause a three or six-pointed-star effect (Asterism) forming the popular star ruby, again in en cabochon cuts.

Cut
Transparent gems quality Rubies (with or without minor inclusions) are cut in all the common shapes. Less transparent rubies are cut en cabochon, with particular care being given to the orientation of the silk to achieve the best possible star or cat's eye effect from the stone

Mineable Deposits

For centuries the Mogok Valley in Upper Myanmar (Burma) was the world's main source for top quality rubies, even though only about 1 percent were gem quality, (giving some idea of the quantity of production from the area). In recent years very few good rubies have been found there, and mining in the region is now on the decline. The very best color in Myanmar rubies is often described as "pigeon's blood" red.  In central Myanmar, the area of Mong Hsu began producing rubies of this quality  during the 1990s and rapidly became the world’s main ruby mining area. More recently high grade Ruby deposits  have been found in Namya (Namyazeik) located in the northern state of Kachin, Myanmar

Second to Myanmar in terms of production volume is Thailand. Deposits in the South East of the country (Chantaburi district) were major producer in the twentieth century with the stones exhibiting a characteristic brown or violet tint, on a red hue. The Thai ruby production has declined significantly since the 1980's.

Cambodia (Pailin area) and Vietnam also boast significant deposits with the stones having an open pinkish overtone to the red hue.

Sri Lanka, another significant producer from deposits located in the southwest of the country in the Ratnapura district. Rubies from that deposits are usually characteristically light red to raspberry red in colour.

In Tanzania the Umba river deposits produce smaller quantities of Rubies often characterised by a purple to brown red colour.

Other deposits of  commercial importance are found in: Afghanistan,  Kenya, and Madagascar. With still less significant deposits in  Australia, Brazil, India, Malawi, Nepal, Pakistan, United States and Zimbabwe.

While Madagascar is currently only a small producer of a characteristically dark orange brown Ruby, there are significant deposit as yet untapped in this country which may make it a major producer in years to come.

Ruby - Common Treatments

Heat Treatment
The most common treatment for Ruby is the application of heat. While initially only stones of a lower quality were treated in this way, estimates now coming for South East Asia indicate that heating is now carried out of about 95% of all rough material, as part  of an industry accepted enhancement technique. Heat treatment is used specifically to improve colour, remove any purple overtones, blue patches and silk. These heat treatments typically occur around temperatures of 1700 - 1800 °C, in computer controlled electric furnaces. Some cutting houses still use the older process of low tube heat, when the stone is heated over charcoal at a temperature of about 1300 °C  for 20 to 30 minutes, a process know in the trade as "Chanthaburi cooking". The silk is only partially broken as the color is improved.

Fracture Filling
Fracture filling falls into two distinct categories, namely intentional and unintentional. In intentional fracture filling lower grade rubies with surface-reaching fissures (cracks)  are often fracture-filled with lead glass. This treatment greatly improves the appearance of the stones to produce an article that can be sold at a very reasonable price. In unintentional fracture filling some of the Borax compound used to encase the rubies during the heat treatment process can partially melt and enter surface reaching fractures. This may or may not enhance the stones appearance, and is a difficult process to prevent unless the heated stones are fissure free.

Important & Famous Ruby

Rubies have long been treasured, and as such there are many examples of famous stones to be found in the museums of the world, in the crown jewels of royal families, and private collections. Some of the more famous stones are the "Edwardes Ruby”, weight 167 ct, currently on display at the British Museum of Natural History in London, the "Rosser Reeves Star Ruby", of 138.7 ct, displayed at the Smithsonian Institution in Washington, and  the "De Long Star Ruby", weight 100 ct, displayed at the American Museum of Natural History in New York.

Interestingly some large rubies, such as the "Black Prince's Ruby" and the "Timur Ruby" in the British Crown Jewels are actually Spinels. This error stemming from missidentification in the 18th century, where it was believed that Spinels were in fact also Rubies.

Ruby - The legend

Throughout history Rubies have been prizes, with many believing that they possessed mystical powers hidden within this intensely coloured red gemstone. The colour of rubies caused many civilizations  through the ages to  associate these beautiful stones with passion, love and romance. Rubies were also thought to bestow wisdom, health and luck, in among other things, gambling. According to oriental beliefs, Rubies are  the “Gems of the Sun.

Ruby is the birthstone for those who are born in July. On the Zodiac chart, Ruby is the stone for Capricorn, and in some cultures Ruby is also used to celebrate a couple's 15th and 40th anniversary.

 

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