Corundum

The corundum group is one of the most significant gemstone species, and it is also the group that contains the greatest number of different kinds of individual members. This oxide of aluminium is likely responsible for producing the wealthiest variety of expensive gemstones that may be discovered in Sri Lanka. stones in alluvial deposits or, less frequently, in source rocks as a result of water wearing them down. The grade of the gemstone corundum is extremely expensive, and specific names are given to the gemstones based on their shade of colour.

Rubies and Sapphires are both classified as corundum, a mineral characterized by its crystalline form of Aluminum Oxide. This significant association remained unknown to the gem trade until 1802, when French Mineralogist Count de Bouron’s chemical analysis revealed that they are essentially distinct variations of the same crystalline mineral.

The vibrant red hue in rubies is attributed to minute amounts of chromium substituting aluminum within the crystal lattice of aluminum oxide. Conversely, the diverse color spectrum exhibited by sapphires results from trace quantities of various elements like titanium, vanadium, cobalt, iron, and nickel being integrated into the corundum crystal.

For instance, titanium and iron impart the blue hue to sapphires, vanadium contributes to purple shades, iron results in yellow tones, and nickel brings about green tinges. The unique pinkish-orange hue of Padparadscha sapphires is influenced by chromium and iron. In contrast, white sapphires consist of pure corundum, devoid of any impurities.

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

Blue Sapphire

Over the course of history, three renowned origins have stood out for blue sapphire stones: Burma, Kashmir, and Sri Lanka, formerly known as Ceylon until 1972. Among these, Sri Lanka, or Ceylon, has maintained its status as the most prolific source of sapphires.

Today, Kashmir sapphires are nearly extinct, with no significant discoveries of new stones in the past century. Burma continues to yield high-quality sapphires, although its primary emphasis is now on ruby mining.

Sri Lanka stands out in the world of precious gemstones, with sapphires constituting 85% of the 130 varieties mined there. Among these, none rival the global appeal of Ceylon Blue Sapphires, renowned for their hue reminiscent of cornflowers.

Primarily sourced from alluvial deposits within Sri Lanka’s highland complex, Ceylon Blue Sapphires, particularly those from the Elahera region, are esteemed for their superior quality. Recent discoveries in the Kataragama klippe, Thammannawa, Kataragama area have added to this reputation.

Across centuries, Sri Lanka’s fame in the gemstone world has been propelled by remarkable finds, making it a sought-after destination for large blue sapphires and blue star sapphires exceeding 100 carats.

Ceylon Blue Sapphires, noted for their lighter and brighter blue tones, have been traded globally since the 2nd Century A.D., prized for their clarity and saturation. Traditionally, the most prized blue sapphires exhibit a velvety blue to violetish hue, ranging from medium to medium-dark tones, characteristics still highly coveted in today’s market.

Noteworthy specimens originating from Sri Lanka, such as the Blue Giant of the Orient, Logan Sapphire, and the Star of Adam, underscore the country’s prominence in the realm of blue sapphires. These gems are celebrated worldwide for their clarity, transparency, and saturation.

Ruby

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.

Padparadscha

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.

Yellow Sapphire

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.

Geuda

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 colors 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.

Chrysoberyl

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

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

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 colorless. Apart from the common varieties of spinel are also varieties identified as Ceylonite, Gahnite and Ghanospinel. The occurrence of natural blue spinel colored 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.

Garnet

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:
• Pyralspite Series
• Ugrandite Series
• Almandine – Fe3Al2(SiO4)3
• Rhodolite
• Grossular – Ca3Al2(SiO4)3
• Andradite – Ca3Fe2(SiO4)
• Pyrope – Mg3Al2(SiO4)3
• Malaya
• Hessonite
• Demantoid
Spessartite – Mn3Al2(SiO4)3
Mali
Tsavorite
Melanite
Uvarovite – Ca3Cr2(SiO4)3
Colour–changing garnet Hydrogrossular
Topazolite
Rainbow garnet

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

Tourmaline naturally results in a wide range of colors and even colour variations in the same gem in concentric or horizontal bands. The noteworthy colors 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 colors could be seen along the length of the crystal and here the colors 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 Aluminum, Magnesium and Iron
• Crystal System – Trigonal
• 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.

Beryl

When beryl absolutely pure in composition beryl should be colorless, but a very close scrutiny of such colorless material will reveal that these are more often than not very faintly tinged with blue, green, pink or yellow. Beryl occurs in different colors, 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 colorless 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 colored 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 colored beryl. The general colour of aquamarine has been often compared to the colour of sea water giving rise to the term aquamarine. The colors are mostly pale or light, the dark shades being less abundant. Aquamarine 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 colors 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.