#97
I422
Example – Ekanite, ThCa2Si8O20
Named for F.L.D. Ekanayake, of Colombo, Sri Lanka, who discovered the mineral.
A mineralogical study and crystal-structure determination of nonmetamict ekanite, ThCa2Si8O20
Szymanski J T, Owens D R, Roberts A C, Ansell H G, Chao G Y
The Canadian Mineralogist 20 (1982) 65-75
http://webmineral.com/data/Ekanite.shtml
CIF
http://rruff.geo.arizona.edu/AMS/download.php?id=05678.cif&down=cif
SiO4 tetrahedra (yellow)
ThO8 polyhedra (green)
CaO8 polyhedra (blue)
The Fascination of Crystals and Symmetry 