Even the cubic melanophlogite often shows anisotropic optical properties.
2.
The International Zeolite Association uses the symbol MEP to indicate the framework topology of melanophlogite.
3.
Melanophlogite is a metastable form of SiO 2 that is stabilized in this structure because of gas molecules trapped in the cages.
4.
Otherwise, melanophlogite is thermally stable and its physical properties do not change upon 20-day annealing at 800 �C, but it converts to cristobalite after heating at temperatures above 900 �C.
5.
Some alkali metal silicides and germanides also form this structure ( Si / Ge at nodes, alkali metals in cages ), as does the silica mineral melanophlogite ( silicon at nodes, linked by oxygen along edges ).
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