Biotite properties

Muscovite mica formed as a primary mineral in pegmatites and granodiorite differs in physical properties compared to muscovite mica formed by secondary alteration (mica schist) (Table 2). The main differences are in flexibiUty and abiUty to be delaminated. Primary muscovite is not as brittle and delaminates much easier than muscovite formed as a secondary mineral. Mineralogical properties of the principal natural micas are shown in Table 3. The make-up of muscovite, phlogopite, and biotite are as follows ... 

Property Muscovite Phlogopite Biotite Synthetic fluorophlogopite... 

Beausoleil N, Lavallee P, Yelon A, Ballet O, Coey JMD (1983) Magnetic properties of biotite. J Appl Phys 54 906-915... 

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... 

Other papers incorporating optical data on micas included Seal et al. (1981), who characterized giant radiohaloes in biotite Finch et al. (1982), who coupled Mossbauer data with their earlier work correlating color with optical properties and Bakhtin et al. 

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... 

Hewitt DA, Wones DR (1975) Physical properties of some synthetic Fe-Mg-Al trioctahedral biotites. Am Mineral 60 854-862... 

H2O. A hydrated biotite mica that has undergone alteration by further hydration. It possesses the peculiar property of exfoliating from 16-20 times its original size on heating. 

Two specific examples of the application of thermodynamic methods to geological problems are considered by Wones and Dodge (biotites as monitors of granitic melts) and by El Goresy and Woermann (opaque minerals as oxygen barometers and geothermometers). These are followed by a section on the thermodynamic properties of melts. Following a review of the properties of "simple" molten salts (Kleppa) the nature and properties of silicate melts are considered by Fraser. This is followed by a chapter by Nicholls on the treatment of activities in natural silicate melts and a discussion of trace element behaviour by O Nions and Powell. 

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. 

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