To come to a précis conclusion about the attribute, quality and category of a gem, using scientific tools is a must. There are numerous scientific tools eligible in examining gems in the area. Among them microscope, refract meter, dichromatic diagram, chemical scale and hand lens are prior in Sri Lanka. Gems graded using these scientific tools are mainly in ten categories. They are namely, Corundum , Zircon, Chrisoberil, Tourmaline, Crystal, Spinel, Beryl, Blue Sapphire, Garnet, Cat’s eye.
Corundum: The category is the salience of all. This is graded into two varieties as Ruby and Sapphire. Varieties of corundum are also called commonly as sapphire. When the gem gleams in red it is classified as ruby and locally it is called “Rathu Keta”. Gem stone will be entitled as sapphire if it is blue, topaz if it is yellow, gold topaz if it is golden and ruby if it is in colour of a lotus flower. Also there are colorless varieties of corundum- white sapphire, Prussian (Kaka Nil) blue and Star sapphire are few examples for achromatic corundum.
Chrisoberil: This is a special and an invaluable brand of gem. Cat’s eye, Kanaka and passingal are several varieties of chrisoberil. Passingal is the most valuable out of them but rarely found. The uniqueness of this stone is its meta spectrum. In daylight it shines green and in factitious light it shines red. That colour would come out even in daylight if a factitious light is made to penetrate the stone.
Cat’s eye (Vairodi): A thin line can be seen in the interior of the stone as same as in a cat’s eye. That line is visible from every direction. Hence, this brand of gem is entitled in English as cat’s eye.
Kanaka: Any kind of Meta spectrum is not visible in this variation of Chrisoberil. It has a light greenish yellow colour.
Crystal: Crystal is an eminent mineral rich in Sri Lanka. Strappy cat’s eye, primrose crystal, amethyst, quartz, roseate crystal and brownish crystal are some varies of crystal plenteous in Sri Lanka.
Beryl: Beryl is a very important mineral treasure. Golden beryl or Heliodorite is also a category of beryl (aquamarine; emerald).
Rabaha (Almandine alias garnet): This is an abounding brand of gem in Sri Lanka. Due to the less chemical composition garnet has a less value in the field of gem. Garnet is categorized as almandine garnet, zircon, spesatyde, and pyros garnet.
Serkin (Chargun): This is an important genus of minerals. According to physical features, Serkin has been divided into two verities. They are also re-divided into subsidiary segments as green Chargun, brown Chargun, yellow Chargun and red Chargun.
Tourmaline: Appeared in various colours such as red, yellow, blue, pink and green, this variety is also an abounding mineral in Sri Lanka.
Spinel: Spinel is an important mineral in corundum family. The spectrum ranges from red, blue and purple to achromatic colors.
Blue Sapphire: Blue Sapphire is always given priority among the valuable gem categories in Sri Lanka. The spectrum ranges from green, brown, yellow, red and blue to achromatic colors.
Poonakkan: A law price mineral which is also called as moonstone (chandrakanthi gem).