Trioctahedral minerals micas

Pelitic rocks investigated in the same areas where corrensites are formed during alpine metamorphism (Kiibler, 1970) revealed the absence of both montmorillonite and kaolinite but the illite or mica fraction was well crystallized as evidenced by measurement of the "sharpness" of the (001) mica reflection (Kiibler, 1968). This observation places the upper thermal stability of the expandable and mixed layered trioctahedral mineral assemblages at least 50°C. above their dioctahedral correlevants. This is valid for rocks of decidedly basic compositions where no dioctahedral clay minerals are present. 

Kato T, Mima Y, Yoshii M, Maeda K (1979) The crystal stracture of IM-kinoshitalite, a new barium brittle mica and IM-manganese trioctahedral micas. Mineral J 9 392-408 Keppler H (1990) Ion exchange reactions between dehydroxylated micas and salt melts and the crystal chemistry of the interlayer cations in micas. Am Mineral 75 529-538 Keusen HR, Peters T (1980) Preiswerkite, an Al-rich trioctahedral sodium mica from the Geisspfad ultramafic complex (Penninic Alps). Am Mineral 65 1134-1137 Knurr RA, Bailey SW (1986) Refinement of Mn-substituted muscovite and phlogopite. Clays Clay Minerals 34 7-16... 

Dioctahedral micas and vermiculites of clay size can be concentrated by differentially dissolving kaolinite and trioctahedral minerals with a fluoride solution proposed by Rich... 

Vermicuhte is an expandable 2 1 mineral like smectite, but vermiculite has a negative charge imbalance of 0.6—0.9 per 02q(0H)2 compared to smectite which has ca 0.3—0.6 per 02q(0H)2. The charge imbalance of vermiculite is satisfied by incorporating cations in two water layers as part of its crystal stmcture (144). Vermiculite, which can be either trioctahedral or dioctahedral, often forms from alteration of mica and can be viewed as an intermediate between UHte and smectite. Also, vermiculite is an end member in a compositional sequence involving chlorite (37). Vermiculite may be viewed as a mica that has lost part of its K+, or a chlorite that has lost its interlayer, and must balance its charge with hydrated cations. 

Hazen R. M. and Wones D. R. (1972). The effect of cation substitutions on the physical properties of trioctahedral micas. Amer. Mineral, 57 103-129. 

The trioctahedral micas can be distinguished by x-ray diffraction from the dioctahedral type. The dioctahedral micas characteristically show distortions that are detected as variations in the bond angles of the hexagonal pattern, Fig. 2.12E (Bailey, 1984). Natural mineral samples often exhibit an occupancy of the B site of greater than 2 and less than 3, producing many variations that cannot be detailed here. 

The maximum amount of Al3+ tetrahedral substitution that 2 1 clays minerals formed at low temperatures can accommodate appears to be 0.80—0.90 per four tetrahedra. While this appears to place an upper limit on the amount of R3+ octahedral substitution, it is not clear why the limit should be such a low value. The dioctahedral smectites can accommodate more substitution (R2 + for R3+) in the octahedral sheet than can the dioctahedral micas. The reverse situation exists for trioctahedral equivalents. In the latter clays octahedral R3+ increases as tetrahedral Al increases. Thus, as one sheet increases its negative charge, the other tends to increase its positive charge. This is likely to introduce additional constraints on the structure. In the dioctahedral clays substitution in either sheet affords them a negative charge and substitution in one sheet is not predicted by substitution in the other sheet thus, one might expect more flexibility. 

Dyar (1987) A review of Mossbauer data on trioctahedral micas evidence for tetrahedral Fe3+ and cation ordering. Amer. Mineral., 72,101-12. 

Dyar, M. D. Bums, R. G. (1986) Mossbauer spectral study of ferruginous one-layer trioctahedral micas. Amer. Mineral., 71,955-65. 

Robbins, D. W. Strens, R. G. J. (1972) Charge transfer ferromagnesian silicates The polarized electronic spectra of trioctahedral micas. Mineral Mag., 38 551-63. 

Aqua regia extraction is a strong partial extraction method that dissolves carbonates, most sulphide minerals, some silicates like olivine and trioctahedral micas, clay minerals and primary and secondary salts and hydroxides (Salminen, 1995). It can be considered a quasi-total extraction method, since actual total concentrations can be higher. On the other hand, this leaching method overestimates the bioavailable amount of toxic elements in a soil since metals trapped in the silicate lattice are released very slowly in the environment and are not easily involved in plant nutrition processes. 

Figure 6 Representation of chemical compositions of potassic, low-temperature micas in space. The poles represent feldspar, dioctahedral clays, and trioctahedral clays, respectively. M = Na, Ca, and especially K ions, R = Al, Fe R = Fe Mg. The compositional positions of the minerals Mu (muscovite) kaol (kaolinite), smectite, and mixed layer mica/smec-tites are indicated. Initial materials are kaolinite (kaol) and iron oxides. A second step is the production of an iron-aluminous smectite and then the formation of either illite via an iUite/smectite mixed layer mineral or glauconite via a glauconite mica/iron-smectite mixed layer phase.

Because they are the dominant mineral in shales, illites, and illite-smectites (see below) are the most abundant of all the clays. Illites are defined as micalike materials less than 2 yttm in size, which, like the micas, have a basal spacing of 10 A (Drever 1988). Most illites are dioctahedral and structurally similar to muscovite, although some are trioctahedral like biotite. Illites contain less and Al and more Si than muscovite. They also usually contain some Mg + and Fe, The irregularity of occurrence of interlayer K+ makes bonding between the layers weaker than in muscovite. Illitic clays... 

Vermiculites occur extensively in soils formed by weathering or hydrothermal alteration of micas. The layer structure of vermiculite resembles that of the mica from which the mineral is derived (Fig. 5.8). Both trioctahedral and dioctahedral vermiculites exist. Weathering or alteration of the precursor micas replaces the interlayer K+ mostly with Mg2+ and expands the c spacing to 1,4-1.5 nm. 

Brigatti MF, Medici L, Saccani E, Vaccaro C (1996a) Crystal chemistiy and petrologic significance of Fe - rich phlogopite from the Tapira carbonatite complex, Brazil. Am Mineral 81 913-927 Brigatti MF, Poppi L (1993) Crystal chemistry of Ba-rich trioctahedral micas-IM. Eur J Mineral 5 857-871 BrownBE (1978) The crystal stmcture of 37 lepidolite. Am Mineral 63 332-336... 

Hazen RM, Finger LW (1978) The crystal stractures and compressibilities of layer minerals at high pressure. 11. Phlogopite and chlorite. Am Mineral 63 293-296 Hazen RM, Finger LW, Velde D (1981) Crystal stracture of a sihca- and alkali-rich trioctahedral mica. Am Mineral 66 586-591... 

Lin C-Y, Bailey SW (1984) The crystal stracture of paragonite-2Mi. Am Mineral 69 122-127 Lin J-C, Guggenheim S (1983) The crystal stracture of a Li, Be-rich brittle mica a dioctahedral-trioctahedral intermediate. Am Mineral 68 130-142... 

Rancour DG, Dang MZ, Lalonde AE (1992) Mossbauer spectroscopy of tetrahedral Fe in trioctahedral micas. Am Mineral 77 34-93... 

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... 

The behavior of micas as a function of P and/or T is therefore strictly dependent on the stacking structural features of these minerals. Thus, trioctahedral and dioctahedral micas show similar responses to thermobaric stress. Most of the compression/expansion occurs along c, at the expense of the interlayer polyhedra. The changes occurring across the (0 0 1) plane are out-of-plane tilting and in-plane rotation of the tetrahedra of the tetrahedral sheets, to minimize the misfit between the tetrahedral and octahedral sheets. 

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