Sri Lanka lies at the southern tip of India which is located at latitude of 6° – 10° N and longitude of 80° – 82° E. The major part of Sri Lanka is made up of Precambrian crystalline rocks except for a belt of sedimentary rocks along the north-west coast of the country. The Precambrian rocks which covers nearly 90% of Sri Lanka, have been classified into three major lithological units, which are Highland / Southwestern Complex, Vijayan Complex and Wanni Complex.
Sri Lanka is well known throughout the world for the large quantity and exquisite variety of its gemstones. These gemstones occur mainly in alluvial gravels found in valley bottoms into which flow tributary hillside streams which carry gem minerals released by weathering form the bed rock sources located at hilltops or hillsides. Apart from the sedimentary formation which carry gemstones some rocks too have been shown to contain gemstones particularly varieties of Corundum. There are also gemstones associated with pegmatite which constituted an important source.
During early times Sri Lanka was once quite fittingly referred to as “Rathna-dweepa” which connotes the meaning “The Island of Gemstones”. The name Rathna-dveepa is found in many chronicles. A Merchants Guide “Periplus of the Erythrean Sea” presumed to have been complied during the first century.
Today around 200 minerals have been classified as gemstones either due to their beauty, durability, rarity or a combination of some of these attribute which should be fulfilled make a mineral worthy of being classified as a gemstone. Of these gemstones, around 75 varieties have been mined or found in Sri Lanka. Although exploitation of Sri Lanka gemstone deposits has been going on for many centuries, its only in reason times that effort has been made to make study of the industry itself, the locations of possible gemstone deposits and most importantly.Main species of Gemstones found in Sri Lanka are as follows.
Corundum as a group is one of the most important gemstone species that has the greatest number of varieties as its members. This oxide of Aluminum probably produces the most important range of valuable gemstones found in Sri Lanka. As water worn pebbles in Alluvial deposits or less frequently in source rocks. The gemstones quality Corundum is highly priced and specific name are given according to the shade of colour such as Ruby for deep red and Padmaraga for pinkish orange or orangish pink. Corundum with colours of lesser importance commercial varieties, being prefixed by the colour name.
Basic scientific details of Corundum family are mentioned below.
Chemical Composition - Al2O3
Crystal System - Trigonal
Hardness – 9.0
Specific Gravity – 3.99
Refractive Index – 1.762 – 1.770
Sri Lanka sapphires are universally renowned for their magnificent quality and the large sizes in which these sometimes occur. Every possible shade of blue is represented among sapphires of Sri Lanka, the various shades ranging from the palest to the darkest. High quality blue sapphires from Sri Lanka are reputed for having pleasing tone of colour of whatever the shades are of remarkable transparency. In superior quality material the Degree of transparency of very high and its clarity is excellent. The most desired coloured and stones for a shapphire has been describe as an instance corn flower blue with a “Velvety” luster. The combination such features those rare, is the pride of Sri Lanka.
Corundum of a red colour are identified as Rubies. Most Sri Lankan varieties are of a pinkish red and display a tint of purple which factor perhaps is sufficient to betray to the experienced person that the stones are of Sri Lankan origin. These purplish tints are attributed to the presence of iron in addition to chromium oxide in the composition. Such stones when subject to instance heat would either lose or diminish the purplish tint thereby highlighting the principle colour, red. This colour is referred to as “Pigeon Blood Red” in gem circles.As a rule, Ruby deposits as such have not been specifically localized in Sri Lanka and are found in association with other members of Corundum family. However, as indicated earlier the stones of better quality have been more often than not found within the Embilipitiya – Udawalawe environs.
The term Padparadscha is a Sinhalese term applied to a very special colour variety of Corundum, so named after the lotus flower as its colour is sometimes akin to a variety of this flower. The Padparadscha has an exceptional colour combination which is very attractive and rare. The colour combination produces the beautiful colour of a sunset at its best as seen across a tropical sky. The colour of Padparadscha is apparently a combination of pink and orange.
Among Yellow Sapphires various shades are noted varying from pale yellow to saffron yellow and from yellow slightly tinted red to a deep citron yellow. In local terminology the Yellow Sapphires are identified as “Pushparaga”. Yellow sapphires are widespread and are found in all Corundum producing areas, one of the most reputed areas being places around Aluthnuwara in the Balangoda region.
Asteriated Sapphires (Star Sapphires)
Asterism is a star like reflection effect caused by certain minerals within the host Corundum. These are microscopic acicular mineral inclusions of special orientation. When these stones cut ‘Cabochon’, displays a special reflection effect in the form of a six, or in rare instances a twelve rayed star on the cabochon surface. Blue, Purple, Pink and Grey coloured Star Sapphires found in Sri Lanka.
On a varietal basis “Geuda” Corundum is one of the more recently appreciated members of the Corundum family. The term Geuda was initially used in Sri Lanka, to describe a property of translucency associated with milky or cloudy appearance seen in some Corundum gemstones. However with heat treatment of Geuda gemstones (a Corundum species) can be converted in to transparent sapphires. The most common Geuda varieties are Diesel Geuda, Milky Geuda, Silky Geuda, Dun Geuda, Ottu and Kowangu Pushparaga. The basic body colour in all these can be pale Blue, Yellow or Pink.
It is thought that of all the Corundum mined in Sri Lanka, about 35 to 40 percent could be categorized as treatable Geuda material in which the colours could be induced through heat treatment. The treatable Geuda Sapphires of Sri Lanka are proven to give better results than Geuda from other part of the world. Sri Lanka is blessed with a large supply of Geuda Sapphires suitable for heat treatment. These deposits are widely spread within the Island.
In Sri Lanka gem chrysoberyl is mostly found as water worn pebbles in the alluvial gem gravels. Chrysoberyl occurs only in a few colours and the common colours being yellow, golden yellow, brownish yellow, yellowish green, bluish green and faint olive green. Chrysoberyl occurs in varying degrees of transparency ranging from transparent and clear to cloudy translucent and opaque. The gemstones of this group are known to have wide distribution in and among the main gem producing regions of this country and are mostly lacalized around Rakwana, Bulutota, Deniyaya, Morawaka, Elahera, Avissawella, Pelawatte, Horana, Matugama, Panadura, Rathnapura, Aluthgama, Ambalantota, Agalawaththa, Bulathsinghala, Kalapugama and Mestiya.
Basic scientific details of Chrysoberyl family are mentioned below.
Chemical Composition - BeO.Al2O3
Crystal System - Orthorhombic
Hardness – 8.5
Specific Gravity – 3.72
Refractive Index – 1.746 – 1.755
Some inclusions make stones cloudy, reduce transparency and produce reflection effects. These if properly oriented would, when cut ‘cabochon’ displays the cat’s eye effect. What is produced is a silvery streak of light which is displayed across the cabochon surface.
Alexandrite is a variety of chrysoberyl is perhaps rarest and Sri Lanka is famous for producing larger stones with fair colour change. The primary beauty of this gem is due to its colour change. At best Sri Lankan stones can be grass green in daylight and violet red to raspberry red in incandescent or artificial light. The gem is priced according the percentage of colour change found in the stone. Although most alexandrite can be faceted, occasionally there is unusual colour changing alexandrite cat’s eye too.
Spinel is a gemstone found in greater abundance in Sri Lanka than either corundum or chrysoberyl. Its very abundance makes Sri Lanka the second largest producer of this stone next to Myanmar (Burma). Sri Lankan spinel range from ruby red, pink, orange, shades of reddish brown, purple, blue, bluish green, mauve, greenish black, black to colourless. Apart from the common varieties of spinel are also varieties identified as Ceylonite, Gahnite and Ghanospinel. The occurrence of natural blue spinel coloured by cobalt has been found in Sri Lanka. Cobalt spinel has been found around Rathnapura, Okkampitiya and Embilipitiya.
Basic scientific details of spinel family are mentioned below.
Chemical Composition - MgO.Al2O3
Crystal System - Cubic
Hardness – 8.0
Specific Gravity – 3.60 | 3.58 - 4.06 (Gahnospinel)
Refractive Index – 1.712 – 1.725 | 1.725 – 1.753 (Gahnospinel)
Original colours are quite different to alexandrite, very often being violet in daylight and changing to reddish Asteriatedspinels with either four or six rays are also found in the gravels of Sri Lanka. Colour changing ‘alexandrite-like’ spinel has also been found from time to time in this country.
Garnets are a group of minerals; which refer to a fairly complex group with a great amount of isomorphic replacement resulting in intermixtures of chemical compositions giving a distinct range of colours.
Of these varieties andradite and uvarovite have not been found in Sri Lanka. As in other gem minerals garnets too occurs in varying degrees of transparency, the fully transparent ones with good colour being the most beautiful. They could also display asterism in the form of a four rayed star. Even chatoyancy has been noted from among the Sri Lankan material as has been established by somebrownish red cat’s eyes. Different varieties of garnets have different properties and these will be discussed separately.
Types of Garnets
Almandine – Fe3Al2(SiO4)3
Grossular – Ca3Al2(SiO4)3
Andradite – Ca3Fe2(SiO4)
Pyrope – Mg3Al2(SiO4)3
Spessartite – Mn3Al2(SiO4)3
Uvarovite – Ca3Cr2(SiO4)3
Red and its diverse shades are the commonest colours in which the varieties, pyrope and almandine occur. The beautiful purplish tinted garnets which are fairly abundant in the Matale-Elahera regions are really an intermediate variety between pyrope and almandine. The term Rhodolite seems to be the more acceptable term probably because of its rhododendron-red colour. This intermediate type of garnet is mostly confined to the Elahera regions. Here the colours are extremely fine, the stones clear and transparent and what is more are found in reasonably large sizes. The superior quality of this variety from this region is so renowned that these are sometimes identified as “Elahera garnets” in order to make the variety more specific.
Tourmaline naturally results in a wide range of colours and even colour variations in the same gem in concentric or horizontal bands. The noteworthy colours found in Sri Lanka are yellowish green, dull green, honey yellow brown and rarely blue and bright green. The yellowish brown tourmalines are more abundant in Sri Lanka compared to other colour varieties. Attractive pink, bi-colour and Paraiba tourmalines are not found in Sri Lanka. The different colours could be seen along the length of the crystal and here the colours are at the two ends where the colour demarcations are very sharp.
Basic scientific details of tourmaline family are mentioned below.
Chemical Composition - Complex borosilicate of Aluminium, Magnesium and Iron
Hardness – 7.0 - 7.5
Specific Gravity – 3.01 – 3.11 (black 3.15 - 3.26)
Refractive Index – 1.62 – 1.66
The red and reddish varieties are identified as rubellite and in instances where the shade of red carries a purplish tint, these are identified as siberite. These varieties are not known to occur in Sri Lanka. Sri Lankan green products have always been of a dull green. These are more yellowish green in appearance. Most of the brown and yellowish brown varieties are located mainly around Uva, Rathnapura and Tissamaharama regions. The brown, brownish yellow and the honey yellow colour varieties are broadly identified as uvaite and dravite respectively. Uvaite has been named after the province of Uva where these varieties are most abundant and widespread. The other areas in which tourmalines are found widespread and in fair abundance are the Lunugala, Bibile, Passara, Nilgala region, Horana, Matugama, Pelawatte, Morawaka, Deniyaya, Rakwana areas, around Rathnapura, Avissawella, Haputale and also around Ambalantota in the south.
When beryl absolutely pure in composition beryl should be colourless, but a very close scrutiny of such colourless material will reveal that these are more often than not very faintly tinged with blue, green, pink or yellow. Beryl occurs in different colours, such as grass green, blue-green, yellowish green, yellow, pink and pinkish red. Accordingly different varieties are identified. These are emerald, aquamarine, golden beryl (heliodor), morganite and goshenite. Goshenite is the term applied to the colourless variety.
Basic scientific details of beryl family are mentioned below.
Chemical Composition - Be3Al2(SiO3)6
Crystal System - Hexagonal
Hardness – 7.5 - 8.0
Specific Gravity – 2.70 – 2.80
Refractive Index – 1.56 – 1.59
Green variety of this family is named as emerald. Emerald is the most important member of this family, but this variety is not indigenous to Sri Lanka. Morganite is a pinkish red or pink coloured variety of beryl and this variety is also not found among Sri Lankan gem gravel. The term aquamarine is applied to the pale blue and greenish blue coloured beryl. The general colour of aquamarine has been often compared to the colour of sea water giving rise to the term aquamarine. The colours are mostly pale or light, the dark shades being less abundant. Auamarine of a flawless deep blue or greenish blue colour is undoubtedly a stone of beauty. The depth of colour is most intense in large stones. The colour in smaller stones is comparatively lighter. Generally the colours in aquamarine are very well distributed and large flawless stones are by no means rare. Stones of good quality should be of deep colour and perfect transparency. In Sri Lanka aquamarine has been found in Rathnapura, Rakwana, Morawaka, Hatton, Nawalapitiya, Galle, Matara, Tissamaharama and Lunugamwhera.Asteriated beryl has also been found in Sri Lanka on rare occasions.
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