Dr. Joel Arem
This article covers in great detail the various geographic regions where Ruby and Sapphire (Gem Corundum) are found. Since geographic origin is significant when determining value, this article may assist those wishing to understand the value of rubies and sapphires.
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.
Burma: 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 called byon 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 spinel 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 English 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 waterfall 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 metalliclike 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.
Columbia: Blue and violet sapphires, many showing a distinct color change, are being mined near Mercaderes, Cauca, Columbia, 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 amphibole-zoisite 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.
Inclusions – What do they tell us about origin?
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 rutile needles at 60⁰ angles; silk consisting of hollow tubes plus crystals of rutile, spinel, 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 spinel, 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 60⁰ and 120⁰; 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.
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 1 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 – finest extant examples:
Crown Jewels of England: Edwardes Ruby, 167 carats.
Cathedrale St. Guy, Prague: 250 carats.
Narodni Museum, Prague: 27.11 (Burma)
American Museum of Natural History in New York, NY: 100 (de Long star ruby).
British Museum of Natural History in London: ruby crystal of 690 grams (Burma).
Private Collection: 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.
Smithsonian Institution in Washington, D.C: 138.7 Rosser Reeves star ruby (red, Sri Lanka); 50.3 (violet-red star ruby, Sri Lanka); 33.8 (red star, Sri Lanka).
Lose Angeles County Museum in Los Angeles: Burma crystal 196.1 carats.
Sapphire – finest extant examples:
Smithsonian Institution in Washington, D.C: 423 (blue Sri Lanka, “Logan sapphire”); 330 (blue star, Burma, “star of Asia”); 316 (blue, Sri Lanka, “Star of Artaban”); 98.6 (deep blue, “Bismarck sapphire”); 92.6 (yellow, Burma); 67 (black star, Thailand); 62 (black star, Australia); 42.2 (purple, Sri Lanka); 16.8 (green, Burma)
Private Collection: Black Star of Queensland, oval, found in 1948, 733 carats, world’s largest black star. A yellow crystal of 217.5 carats was found in Queensland in 1946.
Natural History Museum, Paris: le Raspoli, 135 carat brown, lozenge-shaped rough, clean.
Tested by GIA: 5600 carat sapphire cabochon; also Mysore (India) ruby cab of 1975 carats; Montana blue sapphire, cushion-cut, 12.54 carats believed largest stone from this locality.
Diamond Fund, Moscow: 258.8 (blue), fine, lively gem.
Royal Ontario Museum, Toronto, Ontario, Canada: 179.4 (golden yellow, Sri Lanka); 28.6 (padparadscha, Sri Lanka); 43.95 (greenish yellow, Sri Lanka); 193.3 (blue star sapphire).
British mission to Burma, in 1929, saw a 951 carat sapphire, which may be the largest ever found there.
American Museum of Natural History in New York, NY: 536 (blue, “Star of India”); 116 (blue, “Midnight Star”); 100 (yellow, Sri Lanka); 100 (padparadscha, very fine, Sri Lanka); 163 (blue, Sri Lanka); 34 (violet, Thailand).
Iranian Crown Jewels: Hollow rectangular cabochon of 191.6 carats; oval, yellow gem of 119 carats. Also fine Kashmir blue oval, nearly clean, – 75 carats.
Ruby is the most valuable of all gemstones, and sapphire is one of the most popular. Despite the enormous size of these gems as seen in museum and Royal collections, corundums available on the market are usually of more modest size. A 3-4 carat ruby, if of fine quality, is a rare and very expensive gem today. Sapphires of good blue color over 5 carats, if clean, are similarly rare and also valuable.
There is an abundance of good quality small sapphires but not of rubies.
Star corundum is created by the inclusion of rutile needles within the host corundum crystal. The rutile needles within the host corundum crystal. The rutile needles orient themselves according to the hexagonal symmetry of the corumdum, 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 120⁰ 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 (30⁰ apart), resulting in a strong, 12-rayed star.
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 is from the Sanskrit word kurivinda. Ruby and Sapphire come from the Latin words meaning red and blue, respectively. Padparadscha is a Sinhalese word meaning lotus blossom.