Glossary
Corundum
Corundum is the mineral species of ruby and sapphire – crystallised aluminium oxide with a hardness of 9, the hardest natural gem material after diamond. Red corundum is called ruby, all other colours sapphire, such as blue, yellow, pink or padparadscha. The main colouring trace elements are chromium, iron and titanium.
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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 2026-10-04