Geographical Overview of Sapphire By K.T. Ramchandran, FGA Silvia Sequeira, FGA Gemmological Institute of India (GII), Mumbai Rough crystal of blue sapphire. 62 solitaire INTERNATIONAL april 2014
Sapphire is the name given to all colours of corundum other then red. When used on its own, the name implies blue sapphire. The word sapphire may have been derived from many civilizations. In Sanskrit, it is called sauriratna, which means dedicated to Saturn. In Chaldean, it was called sampir, in Greek sappheiros (blue), in Latin saphirus, and in Arabic safir. Rubies and sapphires are essentially two sides of a coin, and closely related to each other. Both gemstones have been admired for their beauty for centuries. Gemmologist Robert Webster described sapphire as a gem of the soul. It is the birthstone for the month of September, and was said to preserve the wearer from envy and to attract divine favour. The exalted members of the same family of corundum, ruby and sapphire possess the same characteristics, as both are crystallized Alumina (Al2O3) and have the same specific gravity (SG), refractive index (RI) and hardness. Ruby s sensual red colour is equally matched by sapphire s vivid and lavish shades of blue. Cornflower blue or peacock blue is the most sought-after colour for sapphire; it is an admixture of regal purple. The most beautiful sapphires in the world are believed to originate from Kashmir in India. Sapphires range from royal blue, which is overshadowed with a shimmer of velvet, to a marine blue, which is filled with a warm glow. Shades of blue also range from an opulent dark blue to a cool ice blue, azure blue, sky blue and an exciting electric blue. Sapphires derive their colour by the addition of the trace elements, iron and titanium oxide. In fact, the combination of iron and titanium are more relevant in the upper rock forming part of the earth s crust, where the sapphire is born. Geographically speaking, most sapphires are metasomatic minerals. Chemical Composition Chemically, corundum consists of crystallised aluminium oxide, which in its purest form, results in colourless sapphire. It turns blue when a small amount of iron and titanium is added. Renowned gemmologist Dr. Edward Gubelin has described the birth of sapphire: Sapphires in Kashmir were formed in pegmatites rich in aluminium and boron. The requisite iron and titanium for the blue coloration originated from the adjacent rock. Sapphires from Australia, Cambodia and Thailand were subjected to completely different conditions: Created by the reaction of aluminium rich molten carbonatite in the deep layers of the earth s crust under high pressure and temperatures, they were transported as the accompanying minerals of volcanic basalt eruptions to the earth s surface to be deposited as a result of weathering of the sedimentary rubble of the valley floors. The sapphires discovered in the sapphire deposits of Andranondambo on Malagasy were created in yet another way: In the contact zone of very ancient, Tech Talk metamorphic formations, impure marble were transformed under metasomatic conditions into coarsely crystalline aluminium rich skarns (calesilicates) accompanied by the crystallisation of blue corundum thanks to the admixture of traces of titanium and iron. Sapphire typically has an integrated colourant titanium oxide (TiO2), which appears as fine rutile needles. This is what gemmologists and traders refer to as silk, a silvery star-like effect which enhances the beauty of the stone. Formation and crystal habit Sapphires are found in pegmatites, metamorphic and alluvial gem gravel deposits. Sapphire crystallises in the trigonal system, but the habit or shape varies with change in locality and/ or colour. The sapphire crystals occur in a common habit of spindle-shaped bipyramids and columnar hexagonal prism. The ends of many bipyramidal crystals are capped by the flat basal face described as barrel-shaped habit. Sapphire (and some ruby) takes the form of a hexagonal bipyramid of twelve triangular faces, six above and six below, meeting at a girdle. This habit may occur in combinations of bipyramids of different inclinations, with the girdle sometimes formed by a narrow hexagonal prism. The ends of many bipyramidal crystals are capped by the flat basal face to give a barrel-shaped habit. The hexagonal bipyramidal habit is common in sapphire crystals from Sri Lanka, and in this form the faces are often deeply striated horizontally. solitaire INTERNATIONAL april 2014 63
The most important sapphire occurrences are in Sri Lanka, Myanmar, Thailand, Tanzania, Cambodia, Australia, Malaysia and the state of Montana in the US. Sapphires are mined mainly from alluvial deposits. In many places, the primary and secondary deposits are seen simultaneously; the best examples of this are Myanmar, Umba Valley in Tanzania, Montana, as well as Kashmir. The deposits in Australia, Thailand and Cambodia are present in alluvial rubble found as a result of weathered volcanoes. Sapphire crystal habits of different locations Kashmir The crystals are mostly spindleshaped hexagonal bipyramids of light blue colour with deep blue tips and partial corroded surfaces. Burma Mostly found as water-worn fragments and blocky to tabular hexagonal prism and bipyramids of even colouration. Polysynthetic twins are common. Sri Lanka Extremely common are spindle-shaped hexagonal bipyramids with growth twins. Barrel shapes and blocky hexagonal prism/pinacoid combinations are also common. Colouration is often irregular. Thailand, Australia, Cambodia & Nigeria Most common are the barrel shapes, hexagonal pyramids and bipyramid spindles. Quality of sapphire Top prices for blue sapphire are paid for stones of an intense blue verging on violet. Large sapphires are more common than large rubies. Colour zoning can be a problem in sapphire; look for stones which have no major zoning problems. Many blue sapphires are too dark in colour, especially those from basalt sources such as Thailand and Australia; such stones are generally inexpensive. Similarly, sapphires which are too light in colour are also inexpensive. The best stones are those which are well cut, eye-clean and most importantly, of intense blue colours. This 22.66-carat Kashmir sapphire pendant was auctioned by Christie s in 2007 for $3 million. Christie s Images Ltd., 2011 Colouration of Sapphire While there is evidence of two or more possible causes for the blue colour of sapphire, the colour mostly results from a combination of iron and titanium, where they have replaced aluminium in the corundum structure. Physical Properties Specific Gravity The SG of pure corundum, synthetic colourless sapphire, is 3.989, but natural ruby and sapphire usually have SG near 3.997. Iron-rich yellow, green and bluegreen sapphire from Australia or Thailand may reach 4.00. Hardness, Fracture, Cleavage and Parting Corundum is 9 on Mohs scale. Ruby and sapphire may be brittle and should be carefully handled. The fracture varies from uneven to conchoidal. There is no cleavage. Parting from exsolved bohmite may occur parallel to the basal plane or rhombohedral faces. Lustre The lustre of sapphire varies from subadamantine to vitreous and is pearly on parting surfaces. Dispersion The dispersion of the stones is only 0.018 so little fire is perceptible. 64 solitaire INTERNATIONAL april 2014
Tech Talk The most important sapphire occurrences are in Sri Lanka, Myanmar, Thailand, Tanzania, Cambodia, Australia, Malaysia and the state of Montana in the US. Absorption Spectra of other Colours of Corundum Iron causes the colours of natural non-ruby corundum occurring, like chromium, as a replacement for aluminium. This is trivalent iron, and less than 1% may be enough to cause colour. What might be thought of as the classic iron spectrum in corundum is that shown by green sapphire in which no other element influences the colour. In blue sapphires from Australia, all three bands are strings and easily seen; on the other hand, Sri Lanka blue sapphires show only a faint 450 nm band. Gemmologists Basil Anderson and James Payne tell us that blue sapphires from Myanmar, Kashmir, Thailand and Montana show a clear 450 nm band accompanied by a smudge on the long-wave side the only trace of the other two bands. Yellow sapphires may also show the three ferric iron hands. Sapphires from Australia, Montana and Thailand show them most clearly, while yellow sapphire from Sri Lanka may show only a faint 450 nm band or none at all (though they do give a characteristic apricot-yellow fluorescence under both types of UV). Vanadium The part played by vanadium in the colouration of gemstones often echoes that of chromium since trivalent vanadium absorbs in similar areas of the visible spectrum. In corundum, vanadium causes the unmistakable slate to purple colours of the material so often offered as, or at least confused with alexandrite. Colour changing sapphire from Myanmar has been reported and the vanadium spectrum is often seen. A colour changing sapphire from a recently reported source in the far south-west of Tanzania showed bluish green in daylight and reddish brown in incandescent light. Most sapphires are inert under X-rays, except the Sri Lankan, Montana and some Indian (Kashmir) stones, which may show a dull red or yellowish orange glow. solitaire INTERNATIONAL april 2014 65
Important Geographical Locations Owing to the irregular distribution of colour in Kashmir rough, the cut stone will also often display very strong colour zoning. However, heat treatment can produce dramatic results with Kashmir sapphires. In terms of habit, Kashmir sapphire bears a strong resemblance to those of Sri Lanka with almost all being spindle-shaped hexagonal bypyramids. Most of the colour is concentrated in a layer at the tips and just beneath the crystal faces, with colourless cores, somewhat similar to Ottu sapphires from Sri Lanka. Owing to the irregular distribution of colour in Kashmir rough, the cut stone will also often display very strong colour zoning. However, heat treatment can produce dramatic results with Kashmir sapphires. beneath the crystal surfaces. Zircon crystal with or without haloes also may be seen in Kashmir sapphires. Most distinctive inclusions are the small black crystals enclosed in larger cavities. Crystalline inclusions in Kashmir sapphire. INDIA KASHMIR Blue sapphires of magnificent colour, possessing a fine corn flower blue with slight milky appearance are found near the Zanskar district of Kashmir. The deposits lay in a small valley about 1 km long by 1.5 km wide near the Zanskar range of north western Himalayas. Sapphire occurs in a pegmatite vein in association with tourmaline, garnet, kyanite and euclase. The sapphires are found in pockets of kaolin derived from the pegmatite. Rough Kashmir sapphires. Polished Kashmir sapphire. Crystals with milky streamers. Disclaimer: This map is for illustrative purposes only and should not be misinterpreted as an endorsement of the political boundaries. Indian map of corundum gem deposits. The inclusions in Kashmir sapphire under magnification reveal numerous exsolved rutile needles and dust-like particles of an unknown nature. Gubelin considered that the haziness was entirely due to minute canals or hollow tubes of slightly brownish colour which run roughly at right angles to hazy bands intersecting at 120-degree angles. Kashmir sapphire may also contain inclusions of green and brown mica. Most rough materials are partially coated with a white clay-like matrix, which fills the pits of heavily corroded surfaces. The clay-like material also appears to be included in many stones with irregular cavities just Crystals with misty haze-like inclusions. Fluid droplet of plagioclase crystal. 66 solitaire INTERNATIONAL april 2014
Tech Talk Other corundum localities in India Kashmir is not the only location in India producing corundum. Other sources exist, but are of lesser importance in world markets, due to the lower qualities of production. in the culet (bottom) area of the faceted stone so that the blue shows through the table though not in any other direction such stones are intriguing and beautiful. Colour change (blue to purple) many be seen in some sapphires. Other corundum localities in India Andhra Pradesh Anantapur, Khammam, Krishna, Kurnool, Nellore, Visakhapatnam and Warangal districts Bellary district: Sea-green sapphire Assam Nongryniew, Khasi Hills: Clear colourless corundum Bihar Unknown locality: Hexagonal crystals coated with a blackish material Karnataka (including Mysore) Bangalore, Bellary, Chikmagalur, Chitradurga, Coorg, Hassan, Kolar, Mandya, Raichur, Shimoga and Tumkur districts Madhya Pradesh Chhattisgarh Orissa Kalahandi, Junagarh and Bolangir districts Rajasthan Tamil Nadu Kangayam, Karur, Palni and Kayal Pattanam areas around Coimbatore, Madurai and Tiruchirapalli and Salem district SRI LANKA In Sri Lanka, sapphires are found in many colours blue, violet, purple, yellow, orange and white. No other source provides a greater variety of hues. The vast majority of Sri Lankan sapphire crystals are unevenly coloured with large areas devoid of colour altogether. Sri Lankan yellow sapphires. In blue sapphire, the cores of crystals are often colourless while the blue hue is concentrated just below the crystal faces in thin layers. Sri Lankan sapphire is rich in mineral inclusions. Among the most important of these inclusions are grains of zircon surrounded by tiny tension fractures creating a halo. Other guest inclusions are apatite, spinel brown slabs of biotite and phologopite mica. Well-formed negative crystals are frequent at times with two phase fillings seen in Sri Lankan sapphires. Healed inclusions consist of negative crystals in fingerprint patterns. Long rutile needles and feathers. Zircon crystals with rutile needles. Virtually all Sri Lankan gems are cut and polished locally. Much blue sapphire shows the nest or only blue in one part of the crystal; lapidaries manage to place the blue Long rutile needles with nest of silk. The name geuda has been used for both the colourless material and the blue crystals resulting when it is heated. The treatment of gemstones for colour improvement is a major concern in the gem trade today, with difficulties arising as much over disclosure as identification. However, heat treatment is more or less an accepted trade practice today, as long as it is disclosed. Feather-like inclusion with long and short rutile needles. The treatment of gemstones for colour improvement is a major concern in the gem trade today, with difficulties arising as much over disclosure as identification. solitaire INTERNATIONAL april 2014 67
The discovery of a high quality blue sapphire deposit in Thammannawa, in the ancient Sri Lankan town of Kataragama, recently started a massive gem rush in the area. The gem deposit was accidentally discovered when sapphire crystals were found in the soil that was being dug up for a road construction project in the Lunugamwehera and Gam Udawa junction leading to Kataragama. PROPERTIES OF SAPPHIRE Species - Corundum Variety - Sapphire Chemical Composition - Al 2 O 3 (Aluminium Oxide) Colour - Any colour other than that designated for ruby. The word sapphire when used alone denotes the colour blue. Crystal System - Trigonal Habit - Prismatic Transparency - Transparent to opaque Lustre - Vitreous Hardness - 9 Pleochroism - Dichroic (strong to weak) Specific Gravity - 3.99 to 4.00 Spectrum - 4500, 4600, 4710 A o Cleavage - 4 directions parting & lamellar twinning Fracture - Conchoidal to uneven Optic Sign - Uniaxial Negative Refractive Index - 1.760 1.768 to 1.770 1.779 Birefringence - 0.008 to 0.009 Dispersion - 0.018 UV Light - Inert Indian Name - Neelam, Shani, Blue sapphire Map of the Thammannawa deposit. Well-formed crystals from this primary deposit display flat faces and sharp edges with an unusually vitreous lustre. The sapphires from this deposit possess good transparency and pure blue colour. Several kilograms of rough materials have been produced so far with some crystals larger than 200 grams. Faceted blue sapphires of fine colour and weighing more than 20 carats have been cut. MYANMAR (BURMA) The most famous locality for fine sapphires is the district around Mogok in upper Myanmar. The Mogok Stone Tract is an area of some 1000 km 2. The area produces fine blue sapphire today. Burmese blue sapphire. Map of the Baw Mar Mine in Mogok. Sapphire from Myanmar is not apparently found in the marble and may have originated in syenites or in pegmatites though specimens are recovered from alluvial deposits. Burma sapphire contains dense clouds of rutile silk with secondary liquid inclusions. The colour of Burmese sapphires is exceptionally even and banding is not found in most specimens. The blue colour of Burmese sapphires is slightly greenish than those of Sri Lanka which has a yellow tint. Compared to Sri Lankan sapphires, rutile silk of Burma sapphire are shorter and more densely packed. 68 solitaire INTERNATIONAL april 2014
Tech Talk Fingerprint and rutile needle inclusions. Feather-like inclusion with a fluid cavity. Crystalline inclusions include zircon crystals with or without haloes, spinel, rutile, pyrrhotite, magnetic pyrite, apatite, monazite and phlogopite. Negative crystals are very common in sapphires from Mogok Track. Very characteristic are the fingerprints which appear folded or crumpled like flags in the wind. Blue Sapphires from the Baw Mar Mine in Mogok Burmese blue sapphires from the Baw Mar area show a strong pleochroism from greenish to violet blue when viewed perpendicular and parallel to the c-axis. Most of them under the microscope show multiple twinning with whitish needlelike inclusions (presumably bohemite) at the intersections. Needles, most likely rutile, were found only occasionally, but small platelets and needle-like particles, probably ilmenite, appeared more frequently. Most of the stones contained surface-reaching open and healed fissures, but crystal inclusions of feldspar and mica were occasionally encountered. The sapphires also had a relatively high iron content, low gallium, and very low titanium. Blue sapphires collected from the Baw Mar mine in Mogok showed properties distinctly different from those associated with classic Mogok blue sapphires. The Baw Mar samples, which are formed in syenite which intruded into weathered gneiss, as well as from pockets formed at the exposed leucogranite, typically exhibit greenish to violetish blue colours. VIETNAM The southern Vietnam deposits of sapphires are located at Dark Nong and Binh Thuan in the Dek Lak and Lam Dong provinces respectively. Straight and angular parallel growth features are characteristic of sapphires from Luc Yen and Quy Chau. Quy Chau produces some beautiful orange sapphires, the colour of papaya, as well as dark blue sapphires. THAILAND AND CAMBODIA Important sources for sapphires exist in Thailand and Cambodia. The sapphires are generally dark blue. Fine yellow sapphires occur at Khao Ploi Waen and Bang Ka Cha, while blue sapphires occur mainly at Khao Ploi Waen, Bang Ka Cha and Bo Ram in Thailand and Pailin in Cambodia. The most distinctive features of Pailin sapphire are the included red crystals of mineral uranium pyrochlore. In addition, a number of other crystal guests are found in Pailin sapphires. The liquid-filled fingerprint and feathers in Pailin sapphires are similar to Thai and Cambodian rubies. Coarse negative crystals are also found but whether they have resulted from actual growth or by heat treatment is uncertain. Crystalline and feather-like inclusions. Fingerprint-like inclusions and crystal. Fingerprint-like inclusions with crystals. Important sources for sapphires exist in Thailand and Cambodia. The sapphires are generally dark blue. Fine yellow sapphires occur at Khao Ploi Waen and Bang Ka Cha, while blue sapphires occur mainly at Khao Ploi Waen, Bang Ka Cha and Bo Ram in Thailand and Pailin in Cambodia. solitaire INTERNATIONAL april 2014 69
The centre for the gem trade in this area is the Thai town of Chanthaburi. All gem deposits in this area are derived from iron-rich basalt. The high iron content of the mother rock carries over into the corundum, which is generally darker than the ideal. The stones are found in coarse yellow or brown sand, overlaying a bed of clay or basaltic rock. The beds are mostly within 2.5 m of the surface, but some of the mines are over 6 m deep. These deposits have only been worked to any extent since the late nineteenth century and mining is by simple methods. Blue sapphires are also found in western Thailand in the town of Bo Ploi, in Kachanaburi province. Stones from Bo Ploi appear much like heat-treated Sri Lankan stones displaying strong and uneven colour zoning. Blue colour zoning with crystalline inclusions. Although the sapphires from Thailand are usually described as a single entity, they in fact originate from three different major deposits, each located in an entirely different part of the country. The stones from each deposit possess inclusion suites unique to their particular mine. Map of the sapphire deposits in Thailand and Cambodia. Thai sapphires are slightly milky due to concentration of minute exsolved particles along blue colour zones. Rutile silk are not found in Bo Ploi stones and so no star sapphires are found. AUSTRALIA The discovery of sapphire in New South Wales dates from the mid-19th century but commercial production did not begin until the First World War had ended. Sapphires were found in the alluvium of streams on Frazer s Creek near the town of Inverell in the New England area. There are two major sapphire producing localities in Australia; Anakie in Queensland and New England district in New South Wales. All of the Australian deposits are derived from basalt flows and thus tend to be dark owing to the high iron content. The occurrence of sapphires is very similar to that in eastern Thailand and Cambodia. Colour banding is a common feature of the blue and green stone. Colour banding in an Australian sapphire. Magnifications reveal the concentration of minute exsolved particles which follow the hexagonal colour banding. Virtually all Australian sapphires are heat-treated to remove the silk. Tension fissure in Australian sapphire. Yellow sapphires from Australia possess identical inclusions to those from Chanthaburi Thailand. Australian stones possess thin layers of haematite and little rutile silk just beneath the top and bottom of pinacoid faces. Boehmite needles and the rhombohedral twinning are also found in Australian sapphires. Colourless rounded crystals of feldspar surrounded by glassy tension haloes due to heat treatment also appear in Australian sapphires. Other inclusions also include red or orange crystal, stubby rods and plates of hornblende and mica, fingerprint and feathers. Map of sapphire deposits in Australia. UNITED STATES OF AMERICA: YOGO, MONTANA Sapphire crystals occur in a dark silica poor lamprophyre dike consisting of bioite and pyroxene group minerals. The dike intrudes the Madison limestone and though only a few feet wide, extends for at least five miles. At one time British and American companies worked different ends of the dike and a business venture and then the New Mine Sapphire Syndicate was set up. 70 solitaire INTERNATIONAL april 2014
Tech Talk For some time, sapphires from Yogo were handled by the London firm of Johnson, Walker and Tolhurst, which retains illustrated catalogues featuring Yogo sapphires at the present time. control and good quality cabochon grade and a few facet grade crystals are being recovered. Turkana and its vicinity in north-west Kenya produce dark variously coloured sapphire. TANZANIA Corundum from Tanzania occurs in a wide range of colours including orange, purple, mauve and yellow as well as red, green and blue. The three major corundum producing areas of Tanzania are: Longido, Umba and Morogoro. Montana sapphire deposits. Yogo blue sapphires are almost recognisable from their exceptionally bright but deep colour; the crystals are not usually large. Yogo sapphires make superb melee. Lilac and purple stones can also be beautiful. Without doubt, Yogo sapphires are the most commercially important of all the coloured stones so far found in North America. Sapphires showing a wide range of colours are found in the gravel of the Missouri River in the general neighbourhood of Helena, Montana. Most of the production is routinely heated to give brighter colours. In general, crystals are barrel-shaped though some are flattened and characteristically striated across the flat pinacoid faces. Apart from Yogo specimens, sapphires known to be from Montana are routinely heated. When not heated, sapphires from the gem gravels may show negative crystals. AFRICA: KENYA In 1971, American geologists Tim Miller and John Saul discovered corundum in Tsavo West National Park in the Mangari area. Facet grade crystals were much less plentiful than heavily included cabochon material. The Kenya government of the time appropriated the mines though ownership; disputes took time to resolve and private owners eventually regained Multi-colour sapphires from Umba, Tanzania. Of greater importance are the varieties of sapphire from the Umba river valley in north-eastern Tanzania, near the Kenya border where sapphires are mined from several pits in and around a greyish-green serpentine pipe. The sapphires of Umba occur in various colours often of a pastel shade which is very attractive. Purple and mauve and orange sapphires, in particular, are beautiful. Umba blue sapphires. Sapphires showing a wide range of colours are found in the gravel of the Missouri River in the general neighbourhood of Helena, Montana. Most of the production is routinely heated to give brighter colours. solitaire INTERNATIONAL april 2014 71
Tech Talk Map of Tanzania s gem deposits. Umba sapphires have criss-cross rhombohedral twinning planes with boehmite needles and tiny thin plates or films. Crystals of apatite are a common sight in Umba stones and may range in size from large euhedral or rounded individual crystals to tiny plates or fragments. Micro platelets and needles, possibly of hematite and ilemenite. NIGERIA Since the 1970s, corundums of a blue, green and yellow colour began appearing in world markets. These are basalt-derived stones and tend to be dark in colour. The mines are located in the Kaduna district. MALAWI Malawi corundum has been known at least for the last five years. The deposit at Chimwadzulu Hill is more recent. The area is 145 km south-east of the capital city Liongwe. The area comprises mainly metamorphosed ultramafic rocks with an exposed surface diameter of about 1 km. The surrounding county rocks are Precambrian metasediments metamorphosed into schists and gneisses. The bedrock is deeply weathered on the hill with a surface layer of iron rich red porous clay. Corundum is found in the topsoil and there is good evidence of bedrock resources. The area had been described as a sapphire deposit in which the occasional ruby was found. Naturally coloured sapphire crystals of quality were rare and seemed excellent for heat treatment. Chimwadzulu corundum can be described as ranging from a true pink to a very dark purplish blue. MADAGASCAR Madagascar is an island republic located near the south-east coast of Africa. Geologically it is believed that some millions of years ago, the Madagascar landmass was separated from the other main landmass formed of the super continent of Gondwanaland. Madagascar is blessed with many gem minerals, especially ruby and sapphire. The geology of Madagascar is interesting for numerous rock formations such as magmatic, metamorphic, metsomatic, sedimentary as well as volcanic rocks are correlated in the mineralization of sapphires. One of the recently discovered deposits is Andilamena, about 210 km north-east of the capital Antananarivo where the sapphires are mainly recovered from alluvial deposits. Exemplary sapphire from Skarn are those occurring near Andranondambo in the south of Madagascar, where the sapphires were formed at the beginning of the skarn process initiated by the invasion of a granitic magma and thus forcing the silicium to abandon the limestone which, in the course of extensive regional metamorphism, was altered to marble. Based on different generations of primary fluid inclusions in the sapphire, various successions of solid inclusions and the absence of hibonite inclusions, it is suggested that the Andranondambo sapphires formed during several different metasomatic interactions. Madagascar s corundum deposits. References Gemstones by Edward Gubelin & Franz Xaver Erni Gems by Robert Webster InColor magazine by ICA Ruby & Sapphire by Richard W. Hughes Gems & Gemmology by GIA www.ruby-sapphire.com www.aussiesapphire.com Internal World of Gemstones by Edward Gubelin Photoatlas by E.J. Gubelin & J.I. Koivula Gemstone Properties by K.T. Ramchandran & J. Panjikar R&D Department, Gemmological Institute of India 72 solitaire INTERNATIONAL april 2014