Stilpnomelane
The ratio of ferric vs. ferrous iron varies greatly. An ideal end-member "ferrostilpnomelane" can be represented by K 5 Fe 48 2+ (Si 63 Al 9)O 165 (OH) 48.12H 2 O. An ideal end-member "ferristilpnomelane" (which is thought to result from oxidation after primary crystallization) can be represented by K 5 Fe 48 3+ (Si 63 Al 9)O 216.36H 2 O. Note that neither end-member …
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