What does it look like?
What is it?
Basically, the a-cristobalite is stable at temperature below 270°C then above this temperature, the atoms re-arrange to give rise to the b-cristobalite, the symmetry of the solid changing from tetragonal to cubic. And the silica family does not stop here; there are 11 crystalline polymorphs, plus 2 amorphous (non-crystalline) polymorphs. One of them is particularly interesting: is Keatite, which does not exist in the nature, a pure synthetic SiO2 polymorphs.
You can learn more at SiO2 polymorphs at http://www.quartzpage.de/gen_mod.html.
Where did the structure come from?
The structure comes from a paper of Wyckoff Ralph W.G. published in the german journal for Crystallography, namely “Zeitschrift für Kristallographie”, in 1925.