Guide to Ruby

History, Lore and Appreciation

Throughout humanity, red has represented passion and romance. Ruby, the red gem variety of the mineral corundum, has been engaged for centuries to symbolize those sentiments. 17th Century English poet, Robert Herrick, alluded to both passion and the gems’ color when he wrote:

“Some asked me where the rubies grew, and nothing I did say; but with my finger pointed to the lips of Julia.”

Ruby is mentioned in the Bible – and its value is clearly understood. The remark in Job, “The price of wisdom is above rubies,” is but one of six references.

The name ruby comes from the Latin, ruber, meaning red. While there are several red gemstones enjoyed by humankind, ruby is esteemed and regarded as the very definition of red. Descriptions of ruby’s color have wandered into passions as well, with the relatively old phrase “pigeon’s blood”, sometimes used still to describe a fine ruby. Aside from their red color, ruby and spinel are often mined from the same sources, and interesting historical cases exist where large red spinels were called “balas” rubies. The famous Black Prince’s Ruby, a 170 carat gem that graces the Imperial State Crown of the United Kingdom, nestled next to the famous Cullinan II diamond, is actually a spinel. Worn by successive Kings and Queens since the 1367 (and even in helmets going into battle) the spinel hails from present-day Tajikistan. Almost all large “rubies” reported in historical documents are, in fact, red spinels. The Persian scientist, Abu Rayhan al-Biruni did classify differences between spinel and ruby gemstones in the 11th century.

Portuguese travelers in the 1500s and the French traveller and merchant, Jean Baptiste Tavernier who traded in gemstones in the mid-1600s, identified Ceylon (Sri Lanka) and the Kingdom of Pegu, Myanmar (Burma) as the main sources of ruby. In describing the perils inherent in hunting for gems, he notes that a voyage to Kyatpyen, where ruby was traded, should not be attempted by land:”…on account of the jungles which abound with lions, tigers and elephants,” he wrote. In 1904, traveller V.C. Scott O’Conner described Thabeit-Kyin as the port of Mogok, Burma’s famous ruby and sapphire source: “Through this little postern gate the wealth of Capelan has passed for centuries on its way to the great world; to the treasuries of kings, to the fingers of princes, to the necks of beautiful women; to the making of one, the undoing of another.” And this is exactly how locality fits into appreciation. Because Myanmar (Burma) has produced a standard of quality by which ruby from other localities is often measured, the term “Burmese ruby” has also come to be understood by many in the trade as a quality designation. But designations of that kind require additional qualification, as Myanmar (Burma) produces both fine and commercial quality ruby.

Appreciation for red gems, especially ruby, has a historical genesis in India, especially during the rule of the Mughals in the 1600s, whose leaders, particularly Shah Jahan, had an affinity for ruby, spinel and other gemstones. These were often carved with verses from the Qur’an and worn in turbans, articles of clothing and jewelry. The features of ruby, which have always been appreciated, are those that help define the meaning of gemstone: ruby is beautiful, durable and rare.

Birthstones and Anniversaries

Ruby is the birthstone for the month of July. The 15th and 40th wedding anniversaries are celebrated with ruby.

Description and Properties

A variety of the mineral species corundum, forming in the trigonal crystal system with the chemical composition of Al2O3.

Colors: orange red to strongly purplish red; also brownish red. The dominant color must be red.

Refractive Index: 1.762 to 1.770 (+0.009, -0.005)

Birefringence: 0.008 to 0.010

Specific Gravity: 4.00 (±0.05)

Cause(s) of color: Chromium with possible modifications of color with iron and titanium.

Mohs Hardness: 9

Internal identifying characteristics: Clouds of fine particles and networks of fine rutile needles (called silk), which may intersect at 60 degree angles, are commonly seen in natural ruby. Mineral inclusions and included crystals of zircon, and related stress fractures (called halos) are sometimes seen. Liquid-filled “fingerprint” inclusions are also common. Some of these identifying characteristics may disappear, change or be diminished as a result of heat treatment.


Heating: This treatment dissolves or partially dissolves fine rutile needles thereby increasing the clarity and transparency of the gem. In certain cases, controlled heating helps redefine asterism in star rubies. It may also help remove purplish or brownish color components in some gemstones, resulting in stronger red colors.

Diffusion: The diffusion of color-causing elements through the crystal lattice at high temperature is sometimes performed with the intent of intensifying or altering the color of some rubies.

Oil and dye: Some rubies with surface reaching fissures may be treated with oil or dyes, resulting in stronger colors. The treatments are not considered durable and require special care considerations.

Glass filling in cavities and fissures: High lead content glass is sometimes used to fill surface reaching fissures, pits or cracks in certain rubies/corundum. The treatment increases the transparency of low-grade ruby/ corundum. In some cases, the material is so prevalent that it may require special care considerations.

Collector Quality

Location, or provenance, is particularly important with ruby. A fine ruby with a “Burmese” designation may be perceived by the trade to be more desirable than an equally fine ruby from a different locality, through the beauty of rubies from any locality can compete with gems from Myanmar. Much depends on the choice of the wearer. Color is of extreme importance. The more purely red a ruby is, the more collectible it becomes.

Clarity and size of the gem is also important, though the presence of silk or other inclusions is often valued since it not only points to a gem’s natural origin; it also suggests the gem has not been treated at temperatures high enough to dissolve the silk. Cut or carved ruby with known provenance is also collectible.

Star ruby is rare and collectible especially if the legs of the star reach from girdle to girdle of the cabochon, and are unwavering and sharp. Star ruby often has a milky complexion due to inclusions of rutile,
so depth of color and transparency are additional important factors in valuing and collecting these gems.


Thailand, Myanmar (Burma), Cambodia, Sri Lanka, Kenya, Afghanistan, India, Pakistan, Tanzania, Greenland, Tajikistan, Mozambique, Madagascar, Vietnam, Kenya, Malawi, and Nepal.

Cutting, Care and Cleaning

Ruby is mostly cut in traditional pear, round, oval, cushion and emerald cut outlines. Ruby is extremely durable due to its hardness and toughness – second after diamond on the Mohs hardness scale. Ruby jewelry may be cleaned in an ultrasonic cleaner, or it may be steamed. But this should follow close inspection to determine if there are any surface reaching fissures that could expand, or if oils, dyes or glass filling are present; cleaning could harm the filling material. As with most gemstones, a soft moistened cloth, or a soft bristle toothbrush may be used to clean the gem.

Source: CIBJO Retailer Reference Guide,