Aluminosilicates pyrophyllite

Misc. Aluminosilicates - Attapulgite, Halloysite, Pyrophyllite 48 Quartz - Quartz, Agate... 

Pyrophyllite is the simplest layer aluminosilicate in which two tetrahedral Si04 layers are condensed on to the octahedral A106 layer to produce a three-sheet layer, the composition of the unit cell being [Al2(OH)2(Si205)2]2. Another ideal structure in which A1 is replaced by Mg is that of talc. In both cases the three-sheet layer is electrically neutral and the layers are stacked in the ABAB... sequence. Because of the cohesive strength of this ideal structure, neither pyrophyllite nor talc occurs in the form of the very fine particles which generally characterize clay minerals. 

One of the pitfalls in choosing data and drawing diagrams, such as we have done, is that we may not have considered all the possible reactions in our system. That is, there may be phases that are more stable than the ones we have chosen - we may have chosen metastable phases. This is illustrated in our system by the fact that there is another aluminosilicate phase, pyrophyllite, which has more silica in it than does kaolinite and so is stable at higher values... 

Agalmatolite. An aluminosilicate mineral that is very similar to PYROPHYLLITE (q.V.). 

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