Sapphire is a highly precious gemstone which is the single-crystal form of aluminum oxide, a mineral known as corundum. Gemstone enthusiasts favor the sapphire for its brilliant and magnificent colors, constancy and durability. Being in the corundum group, the sapphire has excellent hardness which is exceeded only by the diamond. It is worth mentioning that the diamond is the world’s hardest stone!
The early people of the world believed that the Earth was embedded in a huge blue sapphire firmament which may explain why blue is associated with anything long term like friendship and feelings. Many women prefer sapphire rings for engagement because sapphire symbolizes love, longing and loyalty.
Ceylon, which is today’s Sri Lanka, is where the oldest sapphires finds are. Sapphire and gem experts can easily recognize a stone from Sri Lanka because of its unique luminosity and light to mid-blue colors.
Most sapphires come in different shades of blue but there are other colors as well like brown, grey, black and other range of in the spectrum. Generally, sapphires with colors other than blue are considered as fancy colored sapphires. Most of the blue sapphires come from Australia and Thailand.
The many shades of blue in sapphires can be attributed to the substitution of titanium and iron in the aluminum oxide crystal lattice. Sapphires which are not well saturated show gray tones. Many jewelers apply heat to natural sapphires in order to improve color.
The common colors for the fancy colored sapphires are purple, yellow and green. Purple sapphires cost less than the blue. This may be because the purple stones contain trace element vanadium. There are many shades of purple sapphires. Yellow and green sapphires are caused by traces of iron in them. Pink sapphires contain chromium. The deeper the pink color the more expensive the pink sapphire becomes. Other fancy colors for sapphires include different shades of brown and orange.
One particular beauty of the sapphire is the change in color depending on lighting condition. For example, some sapphires go from pink in daylight to green in fluorescent light.
Like in rubies, asterism also occurs in sapphires. Asterism is an optical phenomenon where the stone exhibits reflection in the shape of a star. In general, the more complex the asterism is, the more expensive the stone is priced.
A sapphire gemstone is generally valued according to size, transparency, color. But exceptions exist especially for very fine quality stones. The origin of the stone is also included in the criteria. For instance, the Kashmir stones are very expensive because of the area where they were taken from. Burmese and Ceylon sapphires follow closely. Stones claimed to be from any of the areas mentioned need to be certified as such.
There are also synthetic sapphires which are grown in laboratories and used for gemstone as well as scientific purposes. The Ti-sapphire is used in laser applications. Sliced pure sapphire can be used to form transparent crystals used in high quality watches to give the face high resistance to scratching.
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