KURIVINDA KAURUNTAKA Tamil kurundam Corundum is from the Sanskrit word kurivindaIt was the belief of the ancient Persians that the Earth actually rested on an enormous Sapphire and that the reflection from this Sapphire was what gave the sky its blue coloration. . Ruby and sapphire come from the Latin words meaning red and blue, respectively. Padparadscha is a Sinhalese word meaning lotus blossom. Star corundum is created by the inclusion of rutile needles within the host corundum crystal. The rutile needles orient themselves according to the hexagonal symmetry of the corundum, and reflections from these needles provide a chatoyancy. When such material is cut into a cabochon the sheen is concentrated along the top of the stone into three white lines crossing at 120° angles, creating a six-rayed star. Very rarely there are two distinct sets of needles oriented according to the first and second order prisms of the corundum (30° apart), resulting in a strong, 12-rayed star.

Namen of things to become 

Next to diamond, corundum is the hardest mineral known and is very compact and dense, with no cleavage. As a result, corundum is one of the best of all jewelry stones, especially star corundum, which is tough as well as scratch-resistant. Faceted gems are slightly brittle and can be chipped, though much less easily than other gems. Very few ruby deposits are known that can be actively worked, which creates ever greater strain on ruby supply in the marketplace. Many more sapphire deposits are in operation, so the situation here is not as critical.

CORUNDUM: Sapphire, Montana (1.35, 1.77, 1.47, 1.66 // 1.19, 1.10, 1.40, 1.22, 1.30 // 1.03, 1.10, 0.96, 0.95, 2.30)

CORUNDUM: Sapphire, Sri Lanka (2.12, 3.76,4.25,5.21 // 6.05, 3.60, 4.02, 16.12)

CORUNDUM: Sapphire, Umba River, Tazmania (1.98, 1.40, 1.86, 3.41, 3.28 // 0.96, 3.77, 1.46, 2.56, 4.64)

Optics

o = 1.757-1.770; e = 1.765-1.779 (usually 1.760, 1.768).

Uniaxial (-)

See table.

Pleochroism

Very pronounced.

Ruby: strong purplish red/orangy red.

Blue sapphire: strong violet-blue/blue-green. Green sapphire: intense green/yellow-green. Orange sapphire: yellow-brown or orange/colorless.

Yellow sapphire: medium yellow/pale yellow. Purple sapphire: violet/orange.

Brownish orange sapphire: brownish orange/greenish.

Padparadscha: orange-yellow/yellowish orange.

Luminescence

The luminescence of corundum is intense and distinctive in identification.

Ruby: Burma stones fluoresce intensely, red, in SW, LW, and X-rays. Red fluorescence is, however, not diagnostic of country of origin or natural origin. Thai ruby fluoresces weak red in LW, weak or none in SW. Sri Lankan ruby fluoresces strong orange-red in LW, pink (moderate) in SW.

Sapphire: 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. Green 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 sapphire: Strong orange-red in LW, weaker color in SW.

Violet or alexandritelike sapphire: strong red in LW, weak light red in SW.

Colorless: moderate light red-orange in LW. Orange: strong orange-red in LW.

Some sapphires from Sri Lanka, Montana, and Kashmir glow dull red or yellow-orange in X-rays.

Spectral

The spectrum of ruby and sapphire can be used diagnostically.

Ruby: A distinctive spectrum; a strong red doublet at 6942/6928 is notable, and this may reverse and become fluorescent. Weaker lines at 6680 and 6592. Broad absorption of yellow, green, and violet. Additional lines seen at 4765. 4750, and, 4685. (The reversible fluorescent doublet is a sensitive test for the presence of chromium in a corundum. Even mauve and purple sapphires have a trace of Cr and show these lines.)

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. Intermediate sapphire colors are a mixture of the various spectra discussed.

Occurrence

Corundum is a mineral of metamorphosed crystalline limestones and dolomites, as well as other metamorphic rock types such as gneiss and schist; also in igneous rocks such as granite and nepheline syenite. Gem corundums are often found in placer deposits. Non-gem corundum is abundant throughout the world, but gem material is more restricted in occurrence

 Ruby historically comes from the Mogok stone tract. 

The history of the mines here is long, complex, and turbulent. Gems occur in a gravel layer calledbyon at a depth of 20 to 100 feet and are recovered by washing and screening with broad screens and then hand-picking encouraging-looking pebbles. Corundum originates in metamorphic marbles that have largely weathered away. This is the source of the world’s finest rubies.

Thailand: The areas of major importance here are Chantabun and Battambang. The corundum deposits have only been worked in a major way in modern times. Gems are found in a sandy layer within 6 to 20 feet of the surface and are recovered by washing Thai rubies are important on the current market because of the scarcity of Burmese gems.

Cambodia: Pailin in Cambodia is a source of some of the world’s finest sapphires, but the country is not significant as a ruby producer.

Kashmir: Fine sapphires occur in northern India in the NW Himalayas at an elevation of nearly 15,000 feet. The deposit is snowed under most of the year. Gems occur in a pegmatite and in the valley below, in surface debris. Kashmir sapphires have a cloudiness due to inclusions and an extremely good blue color, making them greatly desired, but they are extremely scarce.

Pakistan: Ruby and spinet of fine quality occur in the Hunza Valley on the Pakistan side of the Kashmir Valley. The color is comparable to Burma ruby but the material is heavily flawed.

Sri Lanka: Sri Lanka is a source of many colors of sapphire, as well as ruby and star gems. Gems occur here in a gravel layer known as illam at a depth of up to 50 feet. The material is washed and screened, and gems are recovered by hand-picking. Sri Lanka ruby is not as good as Burma material, and the sapphires are often pale in color but can be very large.

Australia: Anakie, Queensland, is a source of sapphire in blue, green, and yellow shades, as well as some ruby. All are in alluvial deposits; some fine green gems are known, as well as an occasional excellent blue gem. Other occurrences are noted in New South Wales, especially the Inverell district (often referred to as the New England fields). Victoria is a location for green sapphire. Ruby has been found in the Harts Range, Northern Territory.

Montana: Yogo Gulch is a well-known locality for fine blue sapphire of very good color that occurs in igneous dikes. The crystals are very flattened and wafer-like, so it is difficult to cut large, full-cut gems from them. Crystals occur in many different colors and are usually quite small, but the blue stones are extremely fine. This material is often zoned and may have a curious metallic-like luster. Ruby is uncommon here.

North Carolina: At Cowee Creek, in Macon County, small rubies and sapphires are found in stream gravels and soil. The quality is usually poor, but an occasional fine, small ruby is found.

Namibia: At Namaqualand opaque ruby is found that is suitable for cabochons.

Colombia: Blue and violet sapphires, many showing a distinct color change, are being mined near Mercaderes, Cauca, Colombia, probably originating in alkalic basalts. Crystals are prismatic and rounded, up to 3 cm in size. Colors are typically blue, green-brown, and violetish, but some yellow, pink, and red crystals have also been found. The blues are somewhat pale; some asteriated material also exists. The stones are rich in iron and poor in titanium. Metallic rutile crystal inclusions are typical.

Japan: Transparent crystals to 5 cm in amphibolezoisite rock on Mt. Gongen, Hodono Valley Ehime Prefecture.

Scotland: Blue sapphire crystals (cuttable) up to about 45 mm in diameter have been found at Loch Roag, isle of Lewis, Outer Hebrides. Colors are variable, sector zoning observed. Paragenesis similar to that of Pailin, Cambodia. Cut stones are small (maximum 2-3 carats).

Tanzania: Large ruby of fine color and quality is found in green, massive chromiferous zoisite. The crystals are usually opaque, and the rock as a whole is cut as a decorative material, but occasionally some small areas of this ruby are transparent enough to facet. Many colors of sapphire are found in the vicinity of Morogoro, Tanga Province, along with some ruby. The Umba River Valley is a source of fine sapphires in a wide range of colors.

Zimbabwe: Sapphires of various colors are found, often zoned with a creamy-white core and blue outer zone, or vice versa. The crystals are well formed and usually up to 3 inches in diameter. At the Baruta Mine, in Northeast Zimbabwe a deep blue crystal of 3100 carats was found. Zimbabwe is also a source of black star sapphire. Sapphires from here are not well known on the market.

Malawi: Sapphires were found about 1958 at Chimwadzulu Hill.

Kenya: Excellent ruby is known from a small ruby mine. The ruby is pinkish but of fine color and is usually in small sizes.

Afghanistan: Ruby of fine color has come from Jagdalek, near Kabul. This is an ancient source of many of the fine stones of ancient times.

India: Mysore produces poor quality rubies but a significant amount of star ruby. Some of the stones from this area are of excellent quality but are not common.

Brazil: The Matto Grosso area has produced sapphires. Gem corundum is occasionally found in Norway; Finland; Greenland; USSR; Czechoslovakia; Pakistan; Nepal.

CORUNDUM: Sapphire, Sri Lanka, heated geuda
(6.13, 3.89 // 4.00, 2.21, 3.60)

CORUNDUM: Sapphire, Sri Lanka
(184, in gold pendant with diamonds)

CORUNDUM: Ruby, Thailand (3.66), Burma (3.56), Thailand 2.23 // Burma (2.30), Thailand (2.11, 2.07, 3.56)

CORUNDUM: Ruby, Burma (gems 0.8 -1.3, in platinum pin with diamonds)

CORUNDUM: Sapphire-Star sapphire, Sri Lanka (31.87)

. CORUNDUM: Ruby-Star ruby, Sri Lanka (2.75), Burma (2.6, 0.62), India (8.4

CORUNDUM: Ruby, Thailand (2.22, 3.68, 3.35)

Inclusions

In general, Burmese, Thai, and Australian blue sapphires contain crystals of plagioclase feldspars, orthoclase, niobite, columbite, calcite, monazite, zircon,apatite, fergusonite, and thorite. Tanzanian sapphires contain crystals of chlorapatite, pyrite, magnetite, biotite, graphite, phlogopite, zircon, and spinel.

Brazil (Jauru, Matto Grosso): rounded gas-filled discs that resemble bubbles.

Burma (Mogok): short futile needles at 60° angles; silk consisting of hollow tubes plus crystals of rutile, spinet, calcite, mica, garnet; zircon crystals with haloes; color swirls known as treacle.

Thailand: feathers = canals and tubelike liquid inclusions; flat, brownish cavities; twin planes; crystals of niobite, almandine, apatite, pyrrhotite; plagioclase crystals in sapphires. Rutile is absent.

Sri Lanka: long rutile needles; healing cracks; zircon crystals with haloes; flakes of biotite and phlogopite mica; feathers with irregular liquid hoses inside; color zoning is frequent; crystals of spinet, graphite, ilmenite, apatite.

Pakistan (Hunza Valley): phlogopite; chlorite; monazite; spinel; rutile; magnetite; pyrite, calcite.

Cambodia (Pailin): specks of uranian pyrochlore (ruby red color, very small).

Kashmir: yellow and brown feathers and thin films; liquid-filled canals; veil-like lines at 60° and 120°C; cloudy haziness; negative crystals, flat films; rods and tubes.

Tanzania (Umba River Valley): apatite; graphite: pyrrhotite.

Tanzania (Longido): pargasite, spinel, zoisite.

Australia: Discoloration and twin lamellae; rutile crystals;liquid-filled feathers, flat cavities; color zoning is frequent.

Nepal: Undulating veils, strong color zoning, prismatic crystals, margarite.

Malawi (Chimwadzulu Hill): fine tubes; small black crystals and short rods; healed fissures; color zoning.

Stone Sizes

Sapphires, in general, reach a far greater size than do rubies. A ruby of 30 carats is a great rarity, whereas sapphires in museum collections weighing hundreds of carats are not uncommon. The largest rubies come from the chrome-zoisite matrix in Tanzania, but these are not really of gem quality. Fine gem rubies of large size occur in the Sri Lankan gravels, with smaller ones from Burma and Thailand. Enormous sapphires of fine color and transparency have been found in the gem gravels of Sri Lanka and Burma, but most are from Sri Lanka. A 1400 gram ruby was found in Yugoslavia (Prilip) but was not gemmy. Malawi material reaches a size of about 12 carats (sapphire). Large sapphires have been found in Australia; Montana sapphires over I carat are very rare, but the blue ones are magnificent in this size range. In general, a fine blue sapphire over 5- 10 carats is very rare, as is a fine ruby over 3-4 carats on the current market.

Ruby:

Crown Jewels ol England: Edwardes Ruby, 167 carats.

Cathedrale St.-Guy, Prague: 250 carats.

Narodni Museum, Prague: 27.11 (Burma).

American Museum of Natural History (New York): 100 (de Long star ruby).

British Museum (Natural History) (London England): ruby crystal of 690 grams (Burma).

Private Collections:

Historical rubies include a 400 carat Burmese rough that yielded 70 and 45 carat gems. A rough of 304 carats was found about 1890. Also famous are the Chhatrapati Manick and the 43-carat Peace Ruby.

Iranian Crown Jewels: fine buckle of 84 Burma ruby cabs, up to 11 carat size