Sapphire
Hardness 9 specific gravity 3.8-4.05
Refractive index 1.76-1.78 birefringence 0.008
Wear: excellent durability
Sapphire is a general designation of all gemstone grade corundum except red. Its main component is aluminum oxide (Al2O3). Because of its hardness of 9 and high refractive index, it is the most important gem besides diamond.
Sapphire in narrow sense refers to blue sapphire, which is described in this item.
Human understanding of sapphire
Since the middle ages, European gem makers began to call the blue corundum crystal sapphire, which comes from the Latin word sapphire. Some linguists think that the word comes from the Sanskrit word Shani, which means dear to Saturn.
In the middle ages, it was said that sapphire could keep its virginity, discover fraud and betrayal, and protect itself from poisons, pestilence, fever and skin diseases.
Sapphire is the birthstone of September.
Colors and features
Blue sapphire is caused by iron and titanium. Some sapphires may show color changing effect.
Broad sense sapphire color is very rich, including blue, yellow, green, purple, pink, orange and colorless. The sapphire with pure aluminum oxide is colorless, and the natural colorless sapphire is very rare.
Place of Origin
At present, the main producing areas of sapphire are Sri Lanka, Madagascar and Myanmar, and the most famous producing areas are Kashmir, India. Other producing areas include Nigeria, Kenya, South Africa, Tanzania, Mozambique, Cambodia, Montana, Australia, Thailand, etc. China also produces sapphire, but the quality is low, which is difficult to meet the requirements of gem level.
Factors affecting prices
Color, cleanliness and cutting are three main factors affecting the value of sapphire. Generally speaking, rich blue has higher value. In common business ratings, dark blue is described as "Royal" Blue ", the darker blue is described as" cornflower ", but strictly speaking, only high-quality sapphires from Kashmir can be called" cornflower ".
Origin is another factor that affects the value of sapphire. As the Kashmir sapphire mine has dried up in the last century, at present, sapphire in Kashmir has the highest carat unit price, followed by sapphire in Myanmar. In the case of near quality, the unit price of sapphire produced in Myanmar may be twice higher than that produced in Sri Lanka and Madagascar.
Sapphire crystal
Sapphire is a trilateral crystal system, and its common crystal habit is columnar biconical. Stripes may appear on the cone angle and cylinder surface, and triangular growth lines are common on the axial surface, with undeveloped cleavage and excellent toughness.
The common inclusions of natural sapphire include: straight color band, crystal inclusions with stress cracks, rutile inclusions, graphite inclusions with halo ring, negative crystal inclusions and pinnate healing cracks.
Natural forming environment
Sapphire is formed in igneous rock without silicic acid, metamorphic rock rich in alumina oxide and metamorphic zone with thermal acid environment.
Most of the gem sapphires are usually mined from "metamorphic deposits" and "alluvial gem gravel deposits", and may also be found in pegmatites.
optical characteristics
Sapphire is one axis crystal with obvious dichroism and adamantine luster.
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