Few gems have held our attention over millennia as well as sapphire. The pure blue colors and excellent durability of this gem-quality member of the corundum family make for an exceptional gemstone. However, not all sapphires are blue. They come in every color of the rainbow. Except red. All red corundum gems are considered rubies. Blue sapphires are simply called sapphires. Sapphires of other colors are named yellow sapphire, pink sapphire, etc. Sapphires get their extraordinary colors from traces of iron, titanium, chromium, and other elements.
Color is the most important element in estimating the value of sapphire. Hue counts, the closer to a pure blue the better, but saturation is more important. Top sapphires reach vivid saturation. (Many of the gems on the market are actually grayish). Tone is also an important consideration. Dark sapphires are abundant and never reach very high values. (Of course, the same can be said for all dark gems. Too dark and they will only be moderately valuable). The pictures below are a rough illustration of differences in saturation.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Corundum|
|Varieties||Color Change Sapphire, Padparadscha, Star Sapphire|
|Crystallography||Hexagonal (trigonal). Crystals common, often barrel-shaped, prisms with flat ends, sometimes bipyramidal; also massive, granular, in rolled pebbles.|
|Refractive Index||1.757 – 1.779|
|Colors||All non-red corundum is considered sapphire. Colorless, white, gray, blue, blue-green, green, violet, purple, orange, yellow, yellow-green, brown, golden amber, peachy pink, pink, black.|
|Luster||Vitreous to adamantine|
|Polish Luster||Vitreous to subadamantine|
|Fracture||Conchoidal. Slightly brittle, usually tough. Frequent parting.|
|Specific Gravity||3.99 – 4.10; usually near 4.0|
|Luminescence||See "Identifying Characteristics" below.|
|Spectral||See "Identifying Characteristics" below|
|Enhancements||Heat treated: common. Diffusion treatment (places a thin blue coating on colorless sapphire): occasional. Irradiation (turns colorless gems yellow, orange, or light blue.): rare.|
|Special Care Instructions||None|
|Transparency||Transparent to opaque|
|Phenomena||Asterism, color change, chatoyancy|
|Formula||Al2O3 + Fe, Ti, Cr, and other trace elements|
|Optics||RI: o = 1.757-1.770; e = 1.765-1.779 (usually 1.760, 1.768); Uniaxial (-)|
|Etymology||From the Latin sapphirus for blue|
|Occurrence||Metamorphosed crystalline limestones and dolomites, as well as other metamorphic rock types such as gneiss and schist. Also, igneous rocks such as granite and nepheline syenite.|
|Inclusions||See "Identifying Characteristics" below.|
The most highly prized sapphires are from Kashmir. High in the Himalaya mountains, these stones can only be found a few months out of the year. They have excellent coloring, but what sets them apart from all others is their very fine silk. This causes the stone to have a velvety appearance. It creates a glow that minimizes extinction at the same time. This effect is only seen in one other stone: Myanmar ruby.
There is some disagreement about the distinction between pink sapphires and rubies. Some authorities classify corundum gems with a dominant red hue as ruby. Others consider any red corundum, including pink, which is a tint of red, to be ruby.
Sapphire has been popularly associated with royalty and said to protect against poison and fraud. Historically, star sapphires have been associated with the power to divine the future. However, ancient references to sapphires may have been actually referring to lapis lazuli, another striking but gemologically distinct blue stone. Learn more about the myths and romance of sapphires in our article on sapphire symbolism.
Sapphires are highly prized jewelry stones. Determining their geographic origin and whether they are natural or lab-grown is critical.
Identifying Kashmir Sapphire
Kashmir sapphires are special. In addition to their fine color, they have a velvety softness much like a Myanmar ruby. This is caused by very fine silk inclusions inside the gem, which scatter light. Kashmir sapphires have a price structure all their own. Many sapphires are said to have “Kashmir color” or are called Kashmir due to their color. However, simply having fine color is not enough to prove origin.
Fortunately, Kashmir sapphires have a variety of features that make them easy to distinguish. Kashmir is the only place where tourmaline and corundum are found together. You will rarely see tourmaline in a finished gem, but it often shows up on the rough or associated matrix.
The most visible feature of these Kashmir sapphires is their silk inclusion. It is much finer than seen in other sapphires. Its appearance is usually muted, rather than being sharp and clear. This is what is known as being “velvety.” The first picture below shows the traditional fine, or velvety, silk as well as a “streamer” effect. (However, in this concentration it will affect the clarity of the gem). In the second picture, the silk is much lighter, but it is still soft in texture. Occasionally where the silk crosses, you will get “snow flakes” as seen in the third picture.
Silk can take on other distinctive appearances. The silk pattern in the picture below left is called “leather.” The sideways markings are what distinguish leather. The picture below right shows parallel streamers. When alone like this, they are often called “comet tails.”
Kashmir stones have typical sapphire inclusions, but unique to them are elongated zircon crystals. Some of them are much more extreme in length than what is pictured here. These and other inclusions often have streamers.
Another identifying feature is extreme color zoning. You can usually see colorless bands between the blue. This alone would not be sufficient to make a call, but in combination with any of the above features, it tells the tale.
Sapphires can display asterism or the “star effect” due to rutile inclusions in their hexagonal crystal matrix. If this rutile is sufficiently abundant and precisely arranged, proper cabochon cutting can create star sapphires.
Inclusions can also help identify the source of a sapphire. See our article on identifying the origins of corundum gemstones for more information. Some inclusions can help identify a synthetic gem.
- Blue stones: give no reaction, except some blue Thai gems, which fluoresce weak greenish white in SW.
- Sri Lankan blue sapphire: may fluoresce red to orange in LW, light blue in SW.
- Blue color-change gems: weak, light red in SW
- Heat-treated blue gems: sometimes chalky green in SW
- Some African blue gems: moderate to strong orange in SW
- Synthetic blue gems: weak to moderate, chalky blue to yellow green in SW
- Green gems are inert.
- Black gems are inert.
- Sri Lankan yellow sapphire fluoresces a distinctive apricot color in LW and X-rays, and weak yellow-orange in SW. The fluorescence in LW is proportional to depth of color of gem.
- Pink stones show strong orange-red in LW, weaker color in SW.
- Violet or alexandrite-like sapphires show strong red in LW, weak light red in SW.
- Colorless sapphires show moderate light red-orange in LW.
- Orange sapphires show a strong orange-red in the presence of LW.
- Synthetic orange sapphires: very weak, orange to red in SW
- Natural color change sapphires: inert to strong red in LW, inert to moderate red to orange in SW
- Synthetic color change sapphires: moderate orange to red in LW and SW, may fluoresce red in LW and mottled blue in SW
- Natural brown sapphires: usually inert or weak red in LW and SW
- Synthetic brown sapphires: inert to weak red in LW and SW
- Synthetic green sapphires: weak orange in LW, dull, brownish red in SW
- Synthetic pink sapphires: moderate to strong red or orange/red in LW, moderate to strong reddish purple in SW
- Synthetic violet sapphires: strong red in LW, strong greenish blue in SW
- Synthetic colorless sapphires: inert to weak bluish white in SW
- Synthetic yellow sapphires: very weak red in SW
- Some sapphires from Sri Lanka, Montana, and Kashmir glow dull red or yellow-orange when exposed to X-rays.
Spectral/Absorption Spectrum of Sapphire
The ferric iron spectrum dominates these stones. In green and blue-green gems, rich in iron, there are lines at 4710, 4600, and 4500 in the blue-green region. Also lines at 4500 and 4600 may seem to merge and become a broad band. The three bands described are generally known as the 4500 complex and are very distinctive in sapphires. Some blue Sri Lanka sapphires also show a 6935 red fluorescent line, and the 4500 line is very weak in these gems.
- Lines rarely seen in Kashmir sapphires. Heat treated sapphires may show no lines or just at 4500.
- Some flux grown synthetic sapphires have a faint line at 4500, most not diagnostic.
- Synthetic color change sapphires show a line 4740.
- Natural green sapphires show lines at 4500, 4600, and 4700.
- Synthetic green sapphires show lines at 5300 and 6870.
- Natural Purple may show combination of ruby and sapphire spectrum
- Natural Yellow, Australian, 4500, 4600, and 4700
- Other Natural Yellow to Orange-Yellow not diagnostic.
- Yellow and orange line sapphires, 6900, cutoff at 4600. If no iron lines, likely synthetic.
- Orange, if only thin lines in red, fluorescent line at 6900, and flawless, probably synthetic.
Corundum gemstones, both rubies and sapphires, were first synthesized in the early 1900s by a simple flame fusion process. Today, many sapphires on the market are lab grown. To be able to properly identify sapphires, gemologists need to be familiar with several methods such as flame fusion, Czochralski, flux, and hydrothermal. Modern laboratory methods can simulate natural formation conditions so closely that colors and even inclusions look extremely natural. Such stones are difficult for all but the most highly skilled professionals to identify as synthetic. See Synthetic Gemstones and Their Identification and Identifying Inclusions Found in Synthetic Gems for more information.
There are numerous treatment methods for sapphires. For details on what they are and how to distinguish them, see Corundum Treatments.
- Australia: Sapphires from here tend to be dark, although some very fine gems have come from the area. Also of interest are the parti-colored sapphires which are usually yellow and green, or yellow and blue.
- Myanmar (formerly Burma): Produces some very high-quality sapphires. The colors are slightly violet blue, highly saturated, medium to medium dark tone.
- Kashmir: Produces the finest sapphires. They have a velvety texture, similar to Myanmar rubies. The colors are slightly purplish blue, with strong to vivid saturation and medium to medium dark tone.
- Sri Lanka: This ancient source is still producing nice sapphires. They tend to have a light to medium tone and be slightly grayish to violet-blue.
- Montana: Produces sapphires of all colors. Unfortunately, most of them are “steely,” meaning they have grayish saturation. The sapphires from Yogo Gulch are an exception. Their coloring is some of the worlds finest. However, they are small and rarely finish over one carat.
- Thailand: Produces an abundance of blue sapphires. The hues and saturations tend to be fine, although many are strongly dichroic, with a dirty green in one direction. Unless properly cut, the green will show in the finished stone. The stones are also very dark, requiring special cutting to show the color.
For more information on these and other sources of sapphire, see our article on identifying the origins of rubies and sapphires.
- Smithsonian Institution (Washington, DC): 423 (blue Sri Lanka, “Logan sapphire”); 330 (blue star, Myanmar, “star of Asia”); 316 (blue, Sri Lanka, “Star of Artaban”); 98.6 (deep blue, “Bismarck sapphire”); 92.6 (yellow, Burma); 67 (black star, Thailand); 62 (black star, Australia); 42.2 (purple, Sri Lanka); 16.8 (green, Burma)
- Private Collection: Black Star of Queensland, oval, found in 1948, 733 carats, world’s largest black star. A yellow crystal of 217.5 carats was found in Queensland in 1946.
- Natural History Museum (Paris): le Raspoli, 135 carat brown, lozenge-shaped rough, clean.
- Tested by GIA: 5600 carat sapphire cabochon; Montana blue sapphire, cushion-cut, 12.54 carats believed largest stone from this locality.
- Diamond Fund (Moscow): 258.8 (blue), fine, lively gem.
- Royal Ontario Museum (Toronto, Ontario): 179.4 (golden yellow, Sri Lanka); 28.6 (Padparadscha, Sri Lanka); 43.95 (greenish yellow, Sri Lanka); 193.3 (blue star sapphire).
- British mission to Burma, in 1929, saw a 951 carat sapphire, which may be the largest ever found there.
- American Museum of Natural History (New York): 536 (blue, “Star of India”); 116 (blue, “Midnight Star”); 100 (yellow, Sri Lanka); 100 (Padparadscha, very fine, Sri Lanka); 163 (blue, Sri Lanka); 34 (violet, Thailand).
- Iranian Crown Jewels: Hollow rectangular cabochon of 191.6 carats; oval, yellow gem of 119 carats. Also fine Kashmir blue oval, nearly clean, 75 carats.
Please note: these are descriptive terms. Sapphires can’t always be identified by their color alone.
- Adamantine spar, brown, usually opaque but may be translucent to transparent.
- African, usually light in tone.
- Australian, usually very dark, some yellow and green parti-colored.
- Burma or Oriental, slightly violet-blue, highly saturated, medium to medium dark tone.
- Cashmere or Kashmir, velvety, slightly purplish blue, strong to vivid saturation, medium to medium dark tone.
- Ceylon or Sri Lanka, light to medium tone, slightly grayish to violetish blue.
- Gueda, milky stones from Sri Lanka that turn blue when heat treated.
- Montana, all colors, usually light to medium tone, grayish saturation.
- Padparadscha, means lotus flower, pinkish orange
- Thai or Siamese, dark blue.
Yellow sapphire is sometimes misleadingly referred to as “Oriental Topaz” or “King Topaz.” Green sapphire is sometimes misleadingly referred to as “Oriental Emerald.” Purple sapphire is sometimes misleadingly referred to as “Oriental Amethyst.” Consult our List of False or Misleading Gemstones Names for more examples.
Sapphire’s hardness is second only to diamond among natural gems. This makes it a superb jewelry stone. Of course, a heavily included or fractured stone will be less stable. For reasonably clean stones, no special wear or care precautions are necessary. Consult our Gemstone Care Guide for recommended cleaning methods.