Zinnwaldite: octahedral ordering in lithium-iron micas.
Ordering of the octahedral sheet of some lithium-iron micas is proposed on the basis of chemical compositions and crystallographic properties. The model of the ordered sheet has large and small sites in the ratio 2 : 1 and explains all observed properties- the small layer thickness, the "dioctahedral reflections," and the n(120 deg) motif in polytypism.
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