Glossary
Asterism
Asterism is the star effect of certain gemstones: on a domed stone a four- or six-rayed star appears and glides across the surface as the stone moves. It is caused by fine, aligned needles inside, usually rutile. Star rubies and star sapphires are the best-known examples; the sharper and better centred the star, the more valuable.
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- KnowledgeHow to read a gemstone dossierA dossier brings together everything that describes a stone – from the laboratory report to custody. Here is how to read it in the right order.Read more
- Laboratory reportsUnderstanding a laboratory reportA laboratory report is a gemstone's most important document. Which information it contains, how to read it and what it does not say.Read more
- GlossaryAbsorption spectrumWhen light passes through a gemstone, the stone absorbs certain wavelengths – the rest make up its colour.Read more
- GlossaryAfghanistanAfghanistan is an old source of ruby and emerald; both are mined in the mountains of the Hindu Kush.Read more
Updated 2026-10-06