Sapphire
Sapphire is a gemstone variety of the mineral corundum which is typically associated with the color blue and also naturally occur in a wide variety of colors such as blue, yellow, purple, orange, green colors which are also called fancy sapphire. The sapphire which show two or more colors in a single stone is called ‘Parti Sapphires’.
Trace amount of elements such as iron, titanium, chromium, copper or magnesium present during formation are responsible for the color of a sapphire.
The sapphire is one of the three gem varieties of corundum, the other two varieties are Ruby and Padparaksha (a pink orange variety).
- Leucosapphire is the name given to the most transparent colorless variety.
- All Sapphire are pleochroic, changing color when the stone is turned.
- One of the precious variety sapphire is Alexandrite seem blue in day light but reddish or violet under an artificial light.
- Padmaraksha is a very rare variety of sapphire with a delicate pinkish-orange colour.
The sapphire is the third hardest mineral. It's hardness is 9 on mohs scale. Beside of ornamental and nabagraha stone sapphires are also used in some non-ornamental applications, including infrared optical components. Such as in scientific instruments high-durability windows, wristwatch crystal and movement bearings, and very thin electronic wafers, which are used as the msulating substrates of very special-purpose solid state electronics.
DEPOSITS
Host rocks of sapphires are dolomotized line stones, marble, basalt, or pegmatite. It is mined mainly from alluvial deposits or deposits formed by weathering, rarely from the primary rock. Today important sapphire deposits are in Australia, Myanmar, Sri-Lanka and Thailand.
Australian deposits have been known since 1870, The Host rock is basalt, the sapphire are washed out of the weathered debris. Since 1918 good blue qualities sapphire have been found in New South whales.
The alluvial deposits in upper Myanmar near Mogok are partially worked with modern methods and yield sapphire as well as rubies and spinels also. The host rock is pegmatite. In 1966 the largest star sapphire was found here weighing 63000 Carats.
Sapphire have been found in Sri-Lanka since antiquity. The deposits are in the South west of the Island in the region of Ralnapura. The mother rock is dolomotized limestone, which is enclosed in granite gnesis. There are also 30 to 60 cm thick river gravel places called illam locally that are exploited from a depth of 3 to 33 ft. Sapphire are usually light blue. There are also yellow and orange varieties as well as green, pink, brown and nearly colorless stones. Star sapphire is also found.
There are two sapphire deposits in Thailand. One in the region of Chantaburi, South-East of Bangkok, the other one near kanchanaburi, north-west of Bangkok. The host rock is marble or basalt. The deposits formed by weathering are mined.
The most desired sapphires used to come from Kashmir in India. Where the deposits the deposits were situated at the height of 16500 ft in the Zaskar mountain. The deposits have apparently been work out. The host rock is a kaolin-rich pegmatite in crystalline Schist. The Kashmir Sapphire is cornflower blue color, often with silky sheen. Most stones sold today as Kashmir sapphire come from Myanmar.
In the late 1800s sapphire deposits were discovered in Montana (United States). The host rock in andesite dikes. Mining is carried out on the dike rock. Color of sapphire is Pale blue or Steel blue.
There are also significant Sapphire deposits in Brazil, Colombia, China, Kenya, Madagascar, Malawi, Nigeria, Tanzania, Vietnam and Zimbabwe. Isolated star sapphire have been found in Finland.
PROPERTIES
| Species | Corundum |
|---|---|
| Variety | Blue / Yellow / Orange Sapphire |
| ChemComp | Al2O3 (Aluminium Oxide) |
| Crystal System | Trigonal |
| Color | Blue, Yellow, Orange and its combination |
| Cause of color | Blue Sapphire – Iron and Titanium, Yellow Sapphire - Iron, Orange Sapphire(Padmaraksha) – Iron And Chromium |
| Hardness | 9 |
| Specific Gravity | 3.99 to 4.00 |
| Pleochroism | Strong to Weak |
| R.I. Range | 1.760 – 1.768 to 1.770 – 1.779 |
| Optic Sign | U-ve |
| Birefringence | 0.008 to 0.009 |
INCLUSION
Inclusion Found in Blue Sapphire are Crystal, Liquid Films, Feathers, Zonal Structures, Silk. Inclusion in Yellow Sapphire are Crystals, Liquid Films, Feathers, Zonal Structures, Silk, Two-phases.
FAMOUS SAPPHIRE
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Weighing in at 563.35 carats, the Star of India is one of the largest sapphires in the world, with a unique star shape that appears on both sides. |
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Once owned by Mrs. John A. Logan (a prominent US Congressman’s wife), it is 422.99 carats, internally flawless, and the second largest faceted blue sapphire in the world. |
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At 466 carats, the Blue Giant of the Orient is the largest faceted sapphire in the world. In 1907, it disappeared under mysterious circumstances and only resurfaced this century. |
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The cabochon-cut sapphire weighing 104 carats is part of the Royal Crown Jewels of Queen Elizabeth II, and was acquired by her ancestors in the 14th century. |
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The Rockefeller Sapphire is prized for its rich cornflower blue hue and is so named for John D. Rockefeller Jr. It is rumoured to have links to the Indian Maharaja Mir Osman Ali Khan, the last Nizam of Hyderabad. |
SIMMULANT
Simulants of Blue Sapphire are Spinel, aquamarine, cobalt glass, tourmaline, Zircon, Paste etc. whereas yellow Sapphire are Synthetic Yellow Sapphire, Citrine, Synthetic cubic zirconia, Topaz, Zircon, scapolite.
