LEARN
Crystal lab
Short lessons acted out on crystal models: things a photo cannot show. Every 3D crystal here is a model, not a photo.
Loading the structure …
One mineral, different gems
Pure corundum (aluminium oxide) is colourless. A trace of chromium in place of some aluminium turns it pink to red: ruby. Iron together with titanium turns it blue: sapphire. Both together give purple.
Ruby
The sliders show which element, not measured amounts: only traces (well under 1 %) are needed. Where pink sapphire ends and ruby begins is a judgement of colour in the trade, not a fixed amount of chromium. GIA: ruby · GIA: sapphire
Corundum in the encyclopedia