Ruby is the all-around traditional, mystical, and ayurvedic birthstone for the month of July.
Ruby is the red variety of the mineral corundum, an oxide of aluminum (Formula: Al2O3 ). It ranges in color from deep cochineal to pale rose-red, sometimes with a tinge of purple; the most valued is blood red (pink corundum is usually referred to in gemological terminology as pink sapphire rather than ruby). Its coloration comes from traces of chromium which replaces some of the aluminum in its structure. Many rubies are heat-treated to improve their clarity, color, or both. Ruby forms a continuous color succession with pink sapphire, the color deepening with an increase in chromium. Only stones of the darker hues are generally considered to be ruby. It was believed by ancient Hindu and Burmese miners that colorless or pale pink sapphires were rubies that had not completely ripened. Ruby has been mined from the gem gravels of Sri Lanka since 18th century BC.
The name ruby comes from the Latin ruber meaning "red". In Sanskrit, ruby is known as ratnaraj, "king of precious stones". Rubies tend to be small (stones more than 10 carats are unusual) as the presence of chromium has an inhibiting effect on crystal growth--hence the high value of large rubies. Ruby crystals tend to be hexagonal prisms with tapering or flat ends. They occur worldwide in igneous rocks, or as waterworn pebbles in alluvial deposits. Gem-quality ruby is a mineral of much more limited distribution. It 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. Other localities that produce minor amounts of gem material are Afghanistan, Madagascar, Vietnam, Cambodia, and North Carolina and Montana. Bright red, opaque ruby crystals in green zoisite come from Tanzania. Star rubies occur in addition to star sapphires.
The distinction between ruby and other transparent red minerals has been made only relatively recently, and so the term "ruby" has often been misapplied in the past.
Ruby is one of the most historically significant colored stones. Rubies are mentioned four times in the Bible, in association with attributes like beauty and wisdom. Ruby has accumulated a host of legends over the centuries. The glowing red of ruby suggested an inextinguishable flame burning in the stone, even shining through clothing and able to boil water. People in India believed that rubies enabled their owners to live in peace with their enemies. In Burma (a ruby source since at least 600 AD—now called Myanmar) a fine ruby was a talisman of good fortune, bestowing invincibility to warriors who possessed rubies in battle. However, it wasn’t enough to just wear the rubies. They had to insert them into their flesh and make them part of their bodies. Hindus divided ruby into four castes, calling the true Oriental ruby a Brahmin. Someone in possession of a Brahmin was believed to have the advantage of perfect safety. Ancient Hindus believed that those who offered fine rubies to the god Krishna were granted rebirth as emperors.
In classical antiquity, rubies were reputed to banish sorrow, restrain lust, and resist poison. In later times, early cultures treasured rubies for their similarity to the redness of the blood that flowed through their veins, and believed that rubies held the power of life. As a blood-colored stone, ruby was used in the preparation of medicines to staunch bleeding. Russian popular tradition maintains that it is good for the heart, brain, vitality, and for clearing the blood. However, in all these cases, given the confusion that has surrounded the term "ruby", it is not certain what mineral was being used. Ruby also took on an important symbolism for Islam: after his expulsion from paradise and arrival in Mecca, Adam was shown a ruby canopy under which lay a glowing stone--a meteorite. He was introduced to build the Kabah, now the main Muslim shrine, over it.
Ruby retained its importance with the birth of the western world and became one of the most sought-after gems of European royalty and the upper classes. Many medieval Europeans wore rubies to guarantee health, wealth, wisdom, and success in love.