| Popis: |
Al–Ni and Al–Co lizardites have been synthesized at hydrothermal conditions. The two phases display different morphologies: thin, dominantly curved platelets (Al–Ni); and stacks of very thin platy particles (Al–Co). The X-ray diffraction and transmission/analytical electron microscopy studies have been used to make accurate distinctions among different structural types and chemical populations. Al–Ni bearing lizardite includes a 1M polytype and probably very subordinate amounts of chlorite. Al–Co bearing lizardite includes two 1M polytypes with different cell-parameters, one of these consisting of an apparently modulated structure. Chemically, Al–Ni- and specially Al–Co lizardite consist of a mixture of two populations with tetrahedral compositions ~ Si1.8Al0.2 and Si2.0. In contrast with previously described Al-rich serpentines, our serpentines are characterized by an asymmetrical Al distribution, with VIAl on the order of 1.0 atom per formula unit. |
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