Biotite crystal structure

The formation and survival of unstable or metastable micas and clays in sediments and soils at low temperatures reflects kinetic as well as thermodynamic factors. First, the rates of reactions involving solid-aqueous and especially solid-solid transformations in dilute solutions are very slow at low temperatures (most natural waters are dilute )- The slow kinetics of clay transformations reflects small differences in free energy between stable and metastable clays. Also, the occurrence of specific clays is related to the chemistry and crystal structure of source minerals. Thus, illite often results from the weathering of muscovite, and vermiculite results from the weathering of biotite (cf. Drever 1988), consistent with the similar chemistries and structures of these pairs of T 0 T minerals. 

Takeda H, Haga N, Sadanaga R (1971) Stractmal investigation of a polymorphic transition between 2M2-, lA/-lepidohte and 2Mi-muscovite. Mineral J 6 203-215 Takeda H, Ross M (1975) Mica polytypism Dissimilarities in the crystal structures of coexisting IM and 2M biotite. Am Mineral 60 1030-1040 Takeuchi Y (1965) Stractrrres of brittle micas. Clays Clay Minerals 13 1-25... 

Redhammer GJ, Beran A, Schneider J, Amthauer G, Lottermoser W (2000) Spectroscopic and structural properties of synthetic micas on the annite-siderophyllite binary Synthesis, crystal structure refinements, Mossbauer, and infrared spectroscopy. Am Mineral 85 449-465 Rice CM, Williams JM (1969) A Mossbauer study of biotite weathering. Mineral Mag 37 210-221 Richardson SM (1975) A pink muscovite with reverse pleochroism from Archer s Posf Kenya. Am Mineral 60 73-78... 

Brigatit Davoli (1990) Brigatti, M.R Davoli, R Crystal structure refinement of IM plutonic biotites American Mineralogist 75 (1990) 305-313... 

The reasons for seeking to establish such cell-dimension formulas are several (1) They should provide quantitative relations between two properties determined independently, and hence give a check on each determination (2) in some cases, the cell parameters will broadly indicate the chemistry, at least by distinguishing biotites from phlogopites from muscovites (3) the development of adequate cell formulas for all micas (including some of very unusual composition) has refined our understanding of their crystal structures. 

In solids, the immediate structural environment (crystal field) of a metal ion is likely to alter its reduction potential. For example, Fe substituted in a silicate has a potential different from Fe " in Fe(OH)3, and different again from Fe in solution. Structures that stabilize Fe relative to Fe lower the reduction potential of Fe in the solid. Solution properties such as pH are likely to affect these potentials in a manner different from the way they affect solution potentials. It is interesting that, in a recent study of biotite subjected to weathering in the presence of Cu, the reduction of adsorbed to metallic... 

Tepikin EV, Drits VA, Alexandrova VA (1969) Crystal stractrrre of iron biotite and corrstraction of structural models for trioctahedral micas. Proc 4th IntT Clay Conf, Tokyo, p 43-49 Tlili A, Smith DC, Beny J-M, Boyer H (1989) A Raman microprobe study of natrrral micas. Mineral Mag 53 165-179... 

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