Ruby and Sapphire – Identifying Origin
by Joel E. Arem, Ph.D., FGA
“Pigeon’s Blood Red Burmese Ruby.” From the “Valley of Rubies” in Mogok, Mynamar. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
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.
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.
Burma (Myanmar): 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.
Ruby is defined as red corundum. All non-red varieties of corundum are considered sapphires. “Sapphire (Large Yellow Crystal).” Ratnapura, Sri Lanka. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
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.
“Sapphire.” Ratnapura, Sri Lanka. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
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.
“Ruby Heart.” Jegdalik, Sorobi District, Afghanistan. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
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, Russia, the Czech Republic, Pakistan, and Nepal.
This “weird” gemstone was collected in Gamesh Himal, Nepal, in 1894. It has a winding sapphire core and a ruby rind. “Gem Ruby With Sapphire Core.” © Rob Lavinsky, http://www.iRocks.com. Used with permission.
Inclusions – What do they tell us about origin?
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 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.
Star sapphires are highly prized. The star effect or asterism is caused by the presence of rutile inclusions. “Star Sapphire.” Sri Lanka. © Rob Lavinsky, http://www.iRocks.com. Used with permission.
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.
You can see inclusions of crystal sulfide inside this sapphire. Ratnapura, Sri Lanka. “Corundum (Var: Sapphire).” © Rob Lavinsky, http://www.iRocks.com. Used with permission.
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