Ruby, Birthstone for July

 

Ruby, Birthstone for July

Ruby is the July birthstone and part of corundum family of gemstones as are all sapphires. Rubies are the most valuable of all of the color gemstones. Some rubies are more per carat than diamonds. The name ruby comes from the Latin rubrum meaning red. Symbolically it holds the power of life, being that is red like blood. In Sanskrit ruby is ratnaraj meaning the King of all precious stones. An ancient Hindu belief was if you offered a ruby to Krishna he would grant you in you next life to be an emperor. 

Rubies were thought to contain the spark of life. In ancient Asia rubies were thought that they were self-luminous and sometimes called the glowing stone. In India, a ruby would allow the wearer to live in peace with all neighbors, in Burma warriors used ruby for protection in battle. In the middle- ages rubies were thought to grant the wearer good health, wealth wisdom and success in love. Rubies were thought to predict danger to the wearer by turning a darker shade when there was danger, then turning back to original color when the danger had passed. Up until the 20th century most red stones (rubies, garnets, tourmaline and spinel) were called rubies. The famous Timur ruby given to Queen Victoria in 1851 turned out to be a red spinel.

As all corundum, ruby is primarily aluminum oxide, with the trace element of chromium that creates the red color in corundum. Chromium also can cause red fluorescence in ruby creating a glowing look to the gem and adding intensity to the color. The more the element chromium is in the ruby crystal the redder the gem. Ruby is a hard gem, with a rating of 9 on the Mohs scale.

The most important rubies are formed in metamorphic rock like marble. Rubies are found in layers distributed irregularly within the surrounding marble. There are no traces of iron found in these rubies that are hosted in marble. Without any iron present these rubies will fluoresce red.

Other ruby deposits are hosted by basalt. Molten basalt rocks transport ruby from deep in the earth crusts to the surface of the earth. The crystals come from depths of 9 -25miles (15-40 KM). These crystals have trace levels of iron and do not fluoresce and can appear darker in tone.

The color range that would consider corundum ruby is orangey red to purplish red. The finest color would red to slightly purplish red hue with a vivid saturation, having medium to dark tone, often displaying the glowing red fluorescence. Ruby is often described as “pigeon blood” red, which refers to the color of the first drops of blood from a freshly killed pigeon.

Almost all rubies are treated by heat. Heating can intensify the color, decrease or remove zoning, reduce any modifying hues and reduce, remove and make inclusions less visible. It is rare when a ruby is not heated; these of course demand higher prices. When a gem laboratory examines a ruby it will classify them with four descriptions. One can assume a ruby has been heated unless it is known from the source or a laboratory report that is unheated.

The finest rubies have been found in Myanmar.  They are referred to as “Burmese” Many of these rubies have a vibrant red body color, soften by the rutile inclusions, glowing red fluorescence. Rubies have been found in the Mogok region of Myanmar since the 15th century.  It is a mountainous region; most mining is in a 70 square mile area with an elevation of 7000 feet. The rubies are mined directly from the marble as well as in alluvial deposits in nearby riverbed gravel. Most of the gems found in this area are ruby. Another find of rubies in the early nineties in the Mong Hsu region of Myanmar 150 miles southeast of Mogok. This region is near the border of Laos, Thailand and China. These are more commercial grade rubies.

Thailand and Cambodia have been a source for ruby since the 15th century as well. These rubies are find in basalt, have some iron in them do not fluoresce. The iron content will make these rubies slightly brownish and quenches the fluorescence in the gem. They are usually darker than the ones from Myanmar. Heating can make them redder and not as dark. Most of these mines are exhausted.

The island of Sri Lanka has been alluvial mining corundum, sapphire, for over 2000 years. Ruby is a small portion of their corundum production. These rubies can be lighter in tone going to the pink side of red. 

In the late nineties corundum was discovered near Luc Yen in northern Vietnam close to the Chinese border and has yielded ruby hosted from marble bearing rock that is similar to the ruby that is found in Myanmar. 

East Africa is a relatively new source for corundum. There are fewer rubies found than other colors of sapphires. The deposits are marble hosted in Kenya and do fluoresce. In Tanzania in the Umba River Valley the alluvial ruby is in marble host. The color for these rubies is on the orangey red side and most are cabochon grade. In Malawi and Mozambique orange sapphires and some rubies are found, most are untreated. 

 For more information: GIA, AGTA, Gubelin