Example – Nepheline, NaKAl2Si2O6
From the Greek nephele, “cloud,” because it becomes clouded when put in strong acid.
The Structure of Nepheline
Buerger M J, Klein G E, Hamburger G E
American Mineralogist 32 (1947) 197-197
NaO7 polyhedra (green)
SiO4 tetrahedra (orange)
AlO4 tetrahedra (blue)