This stone looks as if it has a bit of a split personality with the different patterns and iridescent colours you can see... 

It is a single, natural stone!  How the light entering the stone is reflected and refracted, from two differently oriented, parallel layers of twinning, is what is affecting the colours we see - just amazing. If they had used gemstones to teach physics at school, I admit I would have paid so much more attention...

Marketed as Rainbow Moonstone, it is in fact a transparent feldspar. The feldspar species as a whole is rather complex and definitely not clear cut in their classifications!

I could not resist adding this stone to the teaching kit – it looks even more stunning in real life.