Sapphire is gem-quality corundum in any color except red, which is sold as ruby. Blue is the classic color, caused by iron and titanium, but sapphires also come in pink, yellow, orange, green, purple, white and color-change varieties. With a hardness of 9 and good toughness, sapphire is one of the most practical gems for jewelry worn every day.
Sapphire and corundum
Corundum is aluminum oxide (Al2O3). It is colorless when pure, and trace elements in the crystal produce its colors. Ruby is the chromium-red variety. Everything else is sapphire, and stones in colors other than blue are called fancy sapphires, usually with the color named first: pink sapphire, yellow sapphire and so on. Colorless corundum is sold as white sapphire.
The causes of color are well studied:
- Blue comes from pairs of iron and titanium atoms that exchange an electron when light hits them, absorbing red and yellow light.
- Yellow can come from iron alone or from color centers involving trapped charges in the crystal.
- Pink and purple come from chromium, sometimes combined with the iron-titanium blue.
- Green usually results from a mix of yellow and blue causes, often in iron-rich stones.
- Color-change sapphire contains a balance of absorptions that looks blue in daylight and purplish in incandescent light.
The page on color in gemstones explains these mechanisms in more depth.
Physical and optical properties
Sapphire crystallizes in the trigonal system, often as tapering, barrel-shaped hexagonal crystals. Its refractive index is about 1.762-1.770, it is doubly refractive, and it shows dichroism. Blue sapphire typically shows violetish blue along the optic axis and greenish blue at right angles to it, so cutters orient the table to bring out the better blue. Australian and other iron-rich sapphires can look dark and inky if the cutter misjudges orientation.
Sapphire has no cleavage but can part along twinning planes. Color zoning in straight, angular bands is common and helps separate natural stones from flame fusion synthetics, which show curved bands. Many sapphires contain rutile silk, crystals and healed fractures. On the Mohs hardness scale, only diamond ranks higher among common gems.
Blue sapphire
The most valued blue sapphires show a velvety, medium to medium-dark, slightly violetish to pure blue with strong saturation. Stones that are too dark look nearly black in dim light, and those with a green or gray modifier sell for less. Light silk can soften the color and spread it evenly across the stone, and the trade prizes this look in Kashmir and some Sri Lankan sapphires.
Fancy sapphires and padparadscha
Fancy sapphires cover the rest of the spectrum. Pink sapphires became much more common after deposits in Madagascar opened in the late 1990s. Yellow sapphire is a traditional favorite in Sri Lanka and Thailand. Green and teal stones come from Australia, Nigeria and Montana among other sources.
Padparadscha is a delicate pinkish orange to orangy pink sapphire, named from a Sinhalese word for the lotus blossom. Sri Lanka is the classic source, and Madagascar and Tanzania also produce it. The color range is narrow and labs do not agree on its exact limits. Some padparadscha-colored stones on the market owe their color to beryllium diffusion, so a lab report matters for any stone sold under the name.
Star sapphire
When fine rutile needles grow along the three directions of the crystal and the stone is cut as a cabochon, light reflecting from the needles forms a six-rayed star. Rarer stones show twelve rays from two sets of inclusions. A good star is sharp, centered and has straight, even rays. Black star sapphires from Thailand and Australia owe their color to iron-rich inclusions. The Star of India, a large blue star sapphire from Sri Lanka, is on display at the American Museum of Natural History in New York. Synthetic star sapphires made by the Linde company from the late 1940s show stars that look too perfect and surface-level. See gemstone optics for more on asterism.
Where sapphires come from
Kashmir
Kashmir sapphires were found in the Zanskar range of northern India in the early 1880s, reportedly exposed by a landslide. The deposit at high altitude was worked intensively for only a few years, and later attempts yielded little. Fine Kashmir stones have a soft, velvety cornflower blue caused by minute inclusions that scatter light, and they remain the benchmark for blue sapphire at auction.
Myanmar
The Mogok area, famous for its rubies, also produces rich, saturated royal blue sapphires. The page on Mogok rubies describes the region.
Sri Lanka
Sri Lanka, historically known as Ceylon, has supplied sapphires for well over 2,000 years from gem gravels around Ratnapura and elsewhere. Ceylon sapphires are typically lighter and brighter blue, and the island also produces yellow, pink, purple, white, star and padparadscha stones. Much pale or milky geuda corundum from Sri Lanka is heated to blue. See gems of Sri Lanka.
Madagascar
Large discoveries near Ilakaka in 1998 turned Madagascar into a major sapphire source almost overnight. Production includes blue sapphires comparable to Ceylon material, along with pink, yellow, purple and padparadscha colors. The page on gems of Madagascar covers the rush and other local gems.
Montana and other sources
Montana has produced sapphires since the 1860s from gravel bars along the Missouri River and from Rock Creek and Dry Cottonwood Creek. Yogo Gulch, found in the 1890s, yields small, evenly colored cornflower blue sapphires that rarely need heating. Thailand and Cambodia, Australia, Nigeria, Tanzania and Kenya also produce sapphire, with basalt-related deposits giving darker, iron-rich stones.
Treatments
Heating is common across the sapphire trade. It can intensify blue, remove silk, lighten overly dark stones and turn pale geuda corundum blue. Heated sapphires are stable and widely sold, and unheated stones command a premium. Other treatments include beryllium diffusion, which can produce orange, yellow and padparadscha colors; titanium surface diffusion, which adds a thin blue skin; glass filling of fractures; and irradiation of some yellow stones, which can fade in light. The sapphire treatments guide explains how each is detected and disclosed.
Synthetics and look-alikes
Synthetic sapphire has been made by flame fusion since the early 20th century, and it is used both as a gem and as an industrial material such as watch crystals. Flux and hydrothermal synthetics also exist. Curved color bands and gas bubbles point to flame fusion material. Look-alikes include blue spinel, tanzanite, iolite, blue glass and kyanite, all of which differ from sapphire in refractive index, specific gravity or both.
What affects sapphire value
Color dominates. For blue sapphire, a strong, pure to slightly violetish blue in medium to medium-dark tone sits at the top. For fancy colors, saturation and purity of hue matter most. Clarity follows: sapphire is a Type II gem in GIA's clarity system, so minor inclusions are normal, and eye-clean stones are the goal. Larger sizes rise steeply in price per carat. Unheated status and origins such as Kashmir, Burma and Ceylon add premiums when backed by a lab report. The guide on how colored gemstones are graded covers these factors more fully.
Care and traditions
Heated and untreated sapphires can be cleaned with warm soapy water, and ultrasonic and steam cleaners are usually safe unless the stone has fractures, fillings or surface diffusion. Glass-filled stones need gentle care. Sapphire is the September birthstone and the traditional gift for a 45th anniversary. Medieval clergy wore sapphire rings, and some ancient writers believed the stone protected its wearer from envy and harm.
Frequently asked questions
Do sapphires come in colors other than blue?
Yes. Sapphire occurs in almost every color, including pink, yellow, orange, green, purple, white and color-change. Only red corundum is called ruby instead.
What is a padparadscha sapphire?
A padparadscha is a pinkish orange to orangy pink sapphire, traditionally from Sri Lanka. Its color range is narrow, and labs differ slightly on where its boundaries lie.
Are heated sapphires worth less?
Heated sapphires are standard in the trade and fully acceptable when disclosed. An unheated sapphire of the same quality sells for more, and the difference grows with size and quality.
Why are Kashmir sapphires so expensive?
The Kashmir deposit produced fine material for only a short time in the 1880s, and its velvety blue stones are rare. Those with lab reports confirming Kashmir origin command very high prices.