Sapphire—A Case of Mistaken Identity

Blue Corundum Crystal

Blue Sapphire Crystal

Although blue sapphire is reputed to be the world’s most popular gemstone, many consumers are unaware that sapphires come in a variety of other hues as well. Pink, yellow, orange, green, and purple sapphires are known collectively as fancy-colored sapphires. Perhaps even more startling is the fact that ruby is the name given to red sapphires. Both sapphires and rubies are varieties of a mineral called corundum.

Yellow Corundum Crystal

Yellow Sapphire Crystal

Ruby Crystal

Ruby Crystal

It is not hard to understand the reasons behind this case of mistaken identity. In the past gemstones were classified by color. This meant that fancy-colored sapphires, blue sapphires, and rubies were all believed to be different minerals. Ruby was known as carbunculus, and it was grouped with red stones like garnet and spinel. Dark-blue stones were referred to as sappheiros in Greek and sapphires in Latin. Exceptionally hard gemstones from the Far East were called oriental topaz (yellow and white sapphire), oriental emerald (green sapphire), and oriental amethyst (purple sapphire).

Pink Sapphire RingBecause they were highly prized, sapphires and rubies were traded thousands of miles from their original sources. Without reference to information from the mines—where structurally similar ruby and sapphire crystals could be found together, and parti-colored crystals might also be discovered—there was little means for deducing their true relationship.

Orange CorundumAs Europe descended into the Dark Ages, the seat of intellectual inquiry passed into the hands of Islamic scholars in the East. While most of these scholars studied ancient Greek and Roman texts, new discoveries and insights were also achieved. Arabic manuscripts dating from AD 600 to 1050 provide our first evidence that fancy-colored sapphires, blue sapphires, and rubies were considered the same mineral. The characteristics used to make these evaluations included the gemstone’s color, hardness, resistance to fire, and source.

Padparadscha SapphireIn the 9th century, for example, the writer Pseudo-Aristotle postulated that several distinctly colored gemstones were all varieties of a single mineral called yakut. Another writer from the 13th century, Mohammad Ben Mansur, delineated six varieties of yakut, each capable of scratching almost all other gemstones. The six varieties were distinguished by color: red, yellow, black, white, green, and blue.

Robert Boyle

_Robert Boyle_ by Johann Kerseboom (c. 1689)

Although the true relationship between fancy-colored sapphires, blue sapphires, and rubies had long been suspected in the East—it was not until the 17th century that Western scholars began to arrive at the same conclusion. The state of Western gemology at the end of the 17th century can be illustrated by Robert Boyle’s  An Essay About the Origine and Virtues of Gems. Boyle used personal observation and experimentation in his studies, and he pioneered the use of crystal habit as an aid to gem identification. He believed that gems obtained their color and medicinal virtues by a mixing of pigments and metallic substances while the gems were liquid, or “soft.”

“It seems not unprobable, that the Colours of divers Gems (for I do not say of all) are adventitious, and were imparted to them, either by some colour’d Mineral Juice, or some tinging Mineral exhalation, whil’st the Gem or Medical stone was either in solutis principiis, or of a texture open enough to be penetrable by Mineral Fumes.”

Cut Blue SapphireBoyle’s novel theories about how stones acquired their color left him open to new ideas about the relationship between rubies and sapphires:

“The Degree of hardness of Rubies and Saphires is oftentimes so equal, that I knew an expert English Jeweller, who for that only reason (for he knew not whence the difference of Colours might proceed) took Rubies and Saphires to be of the same kind of Stone.”

“Jewellers reckon among Saphires not only that sort of Azure Gems which usually pass for such, but also another sort of Stones, because of their Saphirine degree of hardness; though for their want of Tincture they call them white Saphires.”

White Sapphire

White Sapphire Crystal

René Just Haüy

René Just Haüy

As the Europeans claimed new territories in the East in the 17th and 18th centuries, researchers gained access to increasing quantities of gemstones. Among the samples were hard crystals from India called convindum or corivindum. When mineralogists began to study the specimens, similarities in their crystal structure suggested linkages among the different varieties of corundum. Romé de L’Isle and the Abbé René-Just Haüy performed pioneering work in this regard.

Charles Greville

_Charles Greville_ by George Romney

But it wasn’t until the dawn of the 19th century that sapphire and ruby were definitively established as being the same gem species. Credit for the discovery goes to Charles Greville and Comte de Bournon, who in 1798 and 1802 published landmark papers for the Royal Society of London.