Si

Axis: S
End: introverted (negative).
Sign in notation: −
Lattice angle: 247.5°.

Stacks that use Si in ego order

Stack	Ego position
Ne-Fi-Te-Si	4
Ne-Ti-Fe-Si	4
Fe-Si-Ne-Ti	2
Te-Si-Ne-Fi	2
Si-Fe-Ti-Ne	1
Si-Te-Fi-Ne	1
Fi-Ne-Si-Te	3
Ti-Ne-Si-Fe	3