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.
Main species of Gemstones found in Sri Lanka are as follows.
Corundum
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
Blue Sapphire
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.
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.
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 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.
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.
- 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 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.
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
|
Other
Garnet
|
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
|
Melanite
|
|||
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.
 |
| Rhodolite garnet |
Tourmaline
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
- 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 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.
Asteriated beryl has also been found in Sri Lanka on rare occasions.
Quartz
Crystalline
|
Polycrystalline
|
|||
Rock
crystal
|
Chalcedony
|
Jasper
|
Quartzite
|
Quartz
& silica replacements
|
Amethyst
|
Carnelian
|
Aventurine
quartz
|
Tiger’s-eye
|
|
Citrine
|
Sard
|
Silicified
|
||
Smoky
quartz
|
Prase
|
|||
Prasolite
|
Chrysoprase
|
|||
Rose
quartz
|
Agate
|
|||
Moss
agate
|
||||
Onyx
|
||||
Bloodstone
|
||||
 |
| Rose sapphire- Quartz |
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