Sapphire is a gem quality variety of the mineral corundum. It is the second hardest substance on earth after diamond, rating 9 on the Mohs scale of mineral hardness. Corundum itself is not a very rare mineral, but gem quality corundum is extremely rare. Most corundum is opaque to translucent and heavily included, suitable only for industrial use, including the production of abrasives used for sandpaper and machining of metal, plastics and wood. The name corundum comes from the Sanskrit word kuruvindam, meaning "ruby sapphire", while the name sapphire comes from the Persian word safir, derived from the Greek word for blue. In times of antiquity and the Middle Ages, the term sapphire actually referred to lapis lazuli, but in the early 19th century, the description and definition of sapphire was changed to the corundum variety we know today.
While blue is the most traditional and classic color for sapphire, sapphire is actually found in a variety of different colors. Most natural sapphire is quite pale and light in color. Only a small percentage of natural sapphire exhibits vivid and intense colors without some type of treatment or enhancement, the most common being heat-treatment. For many years, only blue sapphire was recognized as 'true' sapphire. Today, all colors of gem quality corundum are known as sapphire, with exception to red corundum, which is classified as ruby. There is no definitive demarcation between red ruby and sapphire; in most cases, near-red sapphire would be classed as inferior colored ruby. Thus, it is common practice to trade near-red sapphire as a quality fancy color sapphire, rather than as a lower grade ruby.
Colored sapphire (other than blue) is often referred to as fancy sapphire, and fancy sapphire is typically traded using color-specific names, such as yellow sapphire, green sapphire or purple sapphire. In the past, there were several misleading names used for fancy sapphire varieties, most of which are no longer used, such as 'Oriental peridot', a term which was used to refer to green sapphire.
Identifying Sapphire
Sapphire is any form of gem quality corundum, other than red. It is the second hardest mineral on earth next to diamond. Sapphire lacks cleavage, but can exhibit a conchoidal, uneven fracture. Chemically, sapphire is an aluminum oxide with a specific gravity or density ranging from 3.95 to 4.03 depending on the specific sapphire variety. Its refractive index ranges from 1.762 to 1.788 and its crystals can exhibit a weak level of double refraction or birefringence (0.008). Sapphire belongs to the trigonal crystal system, structured with three planes of symmetry and four axes. The exact crystal form depends on the specific variety and origin. Owing to sapphire's superior hardness and durability, it's nearly unmistakable, despite the fact that there are several other gem types that occur with similar colors and luster. Some of the most easily confused gem types include spinel, zircon, beryl, tourmaline and chrysoberyl.
Sapphire Gemological Properties:
| Chemical Formula: | Al2O3, Aluminum oxide |
| Crystal Structure: | (Trigonal), double pointed, barrel-shaped, hexagonal pyramids, tabloid shaped |
| Color: | Blue, colorless, pink, orange, yellow, green, purple, black |
| Hardness: | 9.00 on the Mohs scale |
| Refractive Index: | 1.762 - 1.788 |
| Density: | 3.95 to 4.03 |
| Cleavage: | None |
| Transparency: | Transparent to opaque |
| Double Refraction or Birefringence: | 0.008 |
| Luster: | Vitreous |
| Fluorescence: | Blue: none; colorless: orange-yellow, violet |
Origin And Source
Sapphire is found in only a few locations in the world. The three most famous regions for blue sapphire are Kashmir, Burma and Sri Lanka. Sapphire has also been mined in Cambodia, Thailand, Vietnam and India. As of 2007, Madagascar has been leading the world in sapphire production, though Sri Lanka continues to be the only steady producer of fine quality blue sapphire. Sri Lanka and Madagascar produce sapphires in a wide range of colors and whilst Sri Lanka has been a known sapphire source for centuries, sapphire deposits in Madagascar were only recently discovered in 1998. The enormous deposits found in the village of Ilakaka came as a big surprise and led to a gemstone fever reminiscent of the 19th century Californian gold rush. Today, Madagascar and Tanzania are considered to be two of the most important sapphire sources. Australia is also known for significant sapphire deposits, though most Australian sapphire is known to form rather dark in color. In the USA, there are small sapphire deposits found throughout Montana and North Carolina.
The finest quality blue sapphire, based on past auction prices, comes from Kashmir and Mogok, Burma. The finest Kashmir and Burmese sapphires display superb color and clarity without any thermal (heat) treatment. In recent times, limited resources in Burma have led miners to focus on more plentiful Burmese ruby. Some Sri Lankan (Ceylonese) sapphires are also unheated, but nowadays, the majority of sapphires have been heated, diffused or fracture-filled to improve color and clarity, regardless of their origin. The Kashmir mines, high up in the Himalayas, have produced spectacular world-renowned gems, but since the 1920s, virtually no new material has been found. The rare, fine blue sapphires of Pailin, Cambodia were also very highly regarded by gem traders throughout the world. Pailin sapphires ranged in color from light to deep blue, but they possessed a distinctive purity and intensity of color that was unlike any other sapphire sources. Many gem traders graded them as close in quality to Kashmir and Burmese sapphires; and certainly superior to Sri Lankan (Ceylonese), Thai, American, Vietnamese, Indian, African and Australian sapphires.
Almost all the sapphires from around the world are cut and processed in Chanthaburi, Thailand. Along with Kanchanaburi and Trat, Chanthaburi was once one of main sources for Thai sapphire. Sapphire mining in Chanthaburi is mostly finished now, though there are a few small private mining locations scattered throughout the province. There is also a large market for Thai star sapphires that exhibit distinctive golden six-rayed stars. The golden black star sapphire is found nowhere else in the world. Nowadays, Chanthaburi, Thailand has become the main processing and trading center for almost all of the world's sapphires, rubies and other colored gemstones.
Related or Similar Gemstones
Sapphire is a gem quality variety of corundum. It is closely related to ruby, which is corundum distinguished only by its red color. Sapphire of any other color is often referred to by a color-specific name; i.e., yellow sapphire, green sapphire or violet sapphire. Colorless sapphire is sometimes known as leuko-sapphire, and rare pinkish-orange sapphire is known as 'padparadscha', a Sinhalese word for 'lotus flower'. Blue Sri Lankan sapphire is sometimes referred to as 'Ceylon sapphire', even though Sri Lanka is known to produce many colors other than blue. Misleading names like Oriental peridot (green sapphire) andOriental topaz (yellow sapphire) were frequently used in the past, but they are now no longer used or accepted in the gem trade.
There are also a variety of trade names used for specific forms of sapphire, such as star sapphire and color-change sapphire. Ruby-zoisite is a mixture of corundum (ruby) and zoisite (the same material as tanzanite) formed within the same stone. Since sapphire comes in a such a wide variety of colors, it can be easily confused with many other gemstones such as zircon, beryl, chrysoberyl, spinel, tourmaline and quartz. However, sapphire has superior hardness and durability which can easily distinguish it from other similar colored gemstones.
Sapphire is a gem quality variety of corundum. It is closely related to ruby, which is corundum distinguished only by its red color. Sapphire of any other color is often referred to by a color-specific name; i.e., yellow sapphire, green sapphire or violet sapphire. Colorless sapphire is sometimes known as leuko-sapphire, and rare pinkish-orange sapphire is known as 'padparadscha', a Sinhalese word for 'lotus flower'. Blue Sri Lankan sapphire is sometimes referred to as 'Ceylon sapphire', even though Sri Lanka is known to produce many colors other than blue. Misleading names like Oriental peridot (green sapphire) andOriental topaz (yellow sapphire) were frequently used in the past, but they are now no longer used or accepted in the gem trade.
There are also a variety of trade names used for specific forms of sapphire, such as star sapphire and color-change sapphire. Ruby-zoisite is a mixture of corundum (ruby) and zoisite (the same material as tanzanite) formed within the same stone. Since sapphire comes in a such a wide variety of colors, it can be easily confused with many other gemstones such as zircon, beryl, chrysoberyl, spinel, tourmaline and quartz. However, sapphire has superior hardness and durability which can easily distinguish it from other similar colored gemstones.
