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[Roger Warin]

Here is a small perfect ruby whose origin is Malagasy.
I think it's rare to see such an idiomorphic ruby crystal showing off its crystalline class so well.
It illustrates the cover of the monthly newsletter that I publish every month.
In a previous issue I had considered corundum from a general point of view, but also to present its two varieties of color, sapphire and ruby.
On this occasion, I tried to think outside the box by explaining the light absorption mechanisms that produce these colors.
Obviously, I had discussed Fe2 + / Ti4 + charge transfers for sapphire (17 pages).
The November issue of the bulletin explains the ruby (14 pages), in the same way, except that the charge transfer is between O2- / Cr3 +.