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The low-density cubic form of silica (impure), melanophlogite, has a clathrate-type structure that incorporates organic molecules, including long straight-chain hydrocarbons. The structure is analogous to that of the clathrate crystalline hydrates of composition 6X.46H(2)O or 8X.46H(2)O. This is the first known example of a silicate framework structure with the pentagonal dodecahedron as a framework element.
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Barclay Kamb (1965) studied this question.
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