#70
Fddd
Example – Thenardite, Na2SO4
Named after the French chemist, Louis Jacques Thenard (1777-1826).
Anhydrous sulphates. I: Refinement of the crystal structure of celestite, with an appendix on the structure of thenardite
Hawthorne F C , Ferguson R B
The Canadian Mineralogist , 13 (1975) p.181-187
http://webmineral.com/data/Thenardite.shtml
CIF
http://rruff.geo.arizona.edu/AMS/download.php?id=05607.cif&down=cif
SO4 tetrahedra (yellow)
Na (green)
The Fascination of Crystals and Symmetry 