Gem trade glossary
Plain definitions of the words dealers, cutters and exporters use, including Sri Lankan terms such as illam and geuda.
- Illam
- The gem-bearing gravel layer found in Sri Lanka's river valleys and fields. It usually lies under clay and topsoil and is dug out in baskets and washed to recover stones.
- Geuda
- A milky or silky, semi-transparent variety of corundum found mainly in Sri Lanka. It has little value in its natural state, but heat treatment can turn it blue.
- Ratnapura
- A city in Sabaragamuwa Province whose name means 'city of gems' in Sinhala. It is the centre of Sri Lanka's main gem-mining district.
- Padparadscha
- A rare pinkish-orange sapphire. Laboratories apply their own colour criteria, so a stone may be reported differently by different labs.
- Rough
- A stone as it comes from the ground, before cutting and polishing.
- Cabochon
- A stone cut with a smooth, domed top and no facets. Star and cat's eye stones are usually cut as cabochons.
- Faceted
- A stone cut with flat, polished surfaces called facets that reflect light.
- Lapidary
- The art and work of cutting and polishing gemstones. A lapidary is a person who does it.
- Yield
- The weight of the finished stone as a share of the rough it was cut from.
- Parcel
- A group of stones of similar type and quality sold or tracked together.
- Lot
- A quantity of stones bought or sold as one unit, often later split into parcels.
- Memo (consignment)
- Handing stones to another party without selling them. Ownership stays with the sender, and the holder must return the stones or pay by an agreed date.
- Treatment
- Any process other than cutting and polishing that changes a stone's appearance or durability, such as heating, filling, diffusion or irradiation. Treatments must be disclosed to buyers.
- Heat treatment
- Heating a stone to improve its colour or clarity. It is the most common treatment for sapphire and ruby.
- Asterism
- The star effect seen in star sapphire and star ruby, caused by fine needle-like inclusions.
- Chatoyancy
- The thin, moving band of light seen in cat's eye stones.
- Adularescence
- The soft, floating blue glow seen in moonstone.
- Inclusion
- A feature inside a stone, such as a crystal, fracture or needle. Inclusions help identify a stone and affect its clarity grade.
- Provenance
- The documented history of a stone: where it was mined or bought, who cut it, what treatments it has had and who has owned it.
- Laboratory report
- An independent examination by a gemological laboratory stating a stone's identity, treatment status and sometimes origin.
- Carat
- The unit of weight for gemstones. One carat is 0.2 grams.
- NGJA
- The National Gem and Jewellery Authority of Sri Lanka, which licenses gem dealers and clears gem exports.
- CUSDEC
- The Sri Lanka Customs declaration that gem, jewellery and diamond exporters are required to submit.
- FOB value
- Free on board: the value of goods loaded on the vessel or aircraft, excluding international freight and insurance.
- Kimberley Process
- An international scheme that certifies rough diamonds as free of conflict origin.
Keep these details on every stone in GemColony, or read our guides.