Ruby precious gemstone index and mineral information

Ruby is the red variety of the mineral corundum, an oxide of aluminum. It has a purplish-bluish red to yellow-red color. The finest color of ruby is pure red with a hint of blue, which is called “pigeons blood.” The substance that provides the color in ruby is chromium, and in the case of brownish tones, iron is present as well. Only stones of the darker hues are generally considered to be ruby. Rubies often contain inclusions called “silk,” that are caused by needle-like crystals of rutile. These inclusions sometimes form in a certain way as to produce what is known as a “star rub.” The word ruby comes from the Latin word “ruber,” meaning red. In Sanskrit, ruby is known as ratnaraj, meaning “king of precious stones.”

Ruby crystallizes in the trigonal crystal system, but the habit varies with the variety and locality.  For instance, Burmese rubies typically contain rutile, calcite, apatite, olivine, sphene and spinel inclusions. Ruby crystals tend to be hexagonal prisms with tapering or flat ends. They occur in igneous and metamorphic rocks, or as water-worn pebbles in alluvial deposits. Gem-quality ruby is found in north-central Myanmar, where it occurs in bands of crystalline limestone; in gravels in Thailand with sapphires and spinels; and in the gem gravels of Sri Lanka, where they are called “illam” by the local population and are usually light red to raspberry-red.. The gem-quality Thai rubies have a slightly darker purplish red color but are “cleaner” stones overall, having less rutile needle inclusions and more luster than Burmese rubies. However, in recent years Thai ruby production has been declining.Ruby is a rough stone, it appears dull and greasy, but, when cut, the luster can approach that of a diamond. Ruby is the hardest mineral after the diamond. However, ruby has no cleavage, but has certain preferred directions of parting. The cutting of the rubies occurs in the country where they are mined. It is usually cut to yield the greatest weight but not necessarily the best proportions. The highest quality rubies come from the Mogok area of Burma.

Ruby has been misidentified for hundreds of years. A famous example is the Black Prince’s Ruby, now in the Imperial State Crown of England and part of the Crown Jewels since 1367. It was not until the 19th century that it was discovered to be a spinel. The word ruby was applied to fine garnets as well; “Cape rubies,” “Australian rubies”, and “Arizona rubies” are all garnet. Red tourmaline, has been called “Siberian ruby,” and “balas ruby” is red spinel.

Rubies are faceted or cut en cabochon. Trapiche rubies are mainly sought after by collectors and consist of a wheel-like growth of several prismatic ruby crystals. When cut or ground flat, trapiche crystals have the appearance of a wheel with black spokes.

Synthetically made rubies started to be made toward the end of the nineteenth century, using the flame fusion method. Soon they became the first gems to be produced in commercial quantities. Synthetic rubies came to replace the “jewel” rubies which were traditionally used as bearings in watches and precision instruments. A particular good synthetic ruby is produced in Mexico under the name of “Ramaura Rubies,” it is created by the J.O. Crystal Company.To the Burmese, a fine ruby was a talisman of good fortune; it had the power of invincibility. In ancient times it was believed that the ruby banished sorrow, restrained lust, and resisted poison. In Russia it is still believed that the ruby is good as a healing medicine for the heart, brain, vitality, and for clearing the blood. One of the world’s great star rubies, the 100.3 carat De long Star Ruby was discovered in Burma (now Myanmar) in the 1930s, and donated to the American Museum of Natural History in 1938. In 1964 it was stolen. The thieves were caught and the De Long Star Ruby was recovered after the payment of a $25,000 ransom.

Ruby is one of the twelve gemstones of the ceremonial breastplate worn by the high priest Aaron, representing the twelve tribes of Israel as described in the Old Testament book of Exodus, and is also known as the month of birthstone meaning, happiness.

Ruby can be confused with almadite, pyrope, spinel, topaz, tourmaline, and zircon.

Mohs’ hardness: 9