Haüyne

Posted because it's gorgeous.  I don't know whether the specimen at the top of the frame is a cut stone or a natural crystal; the latter wouldn't surprise me, but I don't know.  Anyone?

Hauyne crystallizes in the isometric system forming translucent, vitreous typically twinned crystals with highly variable color (blue, white, gray, yellow, green, pink).

The formula is (Na,Ca)_4-8[Al₆Si₆(O,S)₂₄](SO₄,Cl)_1-2