I Features 1. Basic sell: [SIo4l rro=0.40/1.35=0.30<0.414 4 [Si04]4 Sioa tetrahedron◆ Ⅱ.Features 1. Basic sell: [SiO4 ] rsi/rO＝0.40/1.35＝0.30<0.414 [SiO4] 4- 4－ SiO4 tetrahedron