Muscovite- and phengite-3T: crystal structure and conditions of formation

Amisano-Canesi, Alessandra; Chiari, Giacomo; Ferraris, Giovanni; Ivaldi, Gabriella; Соболева, С. В.

doi:10.1127/ejm/6/4/0489

Cited by 38 publications

(11 citation statements)

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“…The T distribution we determined here is the reverse of that proposed by Pavese et al (1997), who suggested that tetrahedral Al orders into the T1 site. This discrepancy can be ascribed to the presence of talc impurities, in the sample studied previously, which made it necessary to constrain the TÀO and MÀO bond lengths to their values from an earlier investigation (Amisano-Canesi et al, 1994). Both our results and those from Pavese et al (1997) support the hypothesis of energetically non-equivalent T1 vs T2 and M2 vs M3 sites, thus favouring ordered distributions.…”

Section: Comparison With Results From Previous Measurementssupporting

confidence: 81%

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Further study of the cation ordering in phengite 3T by neutron powder diffraction

et al. 2000

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Phengite 3T (Dora-Maira massif, Italian western Alps), with chemical composition K 0.96 Na 0.01 Al 1.44 Mg 0.56 (Si 3.59 Al 0.41 )O 10 (OH) 2 has been investigated using powder neutron diffraction, at the ILL (Institut Laue-Langevin) Facility, on the D2B diffractometer. Data sets were collected at 293 and 873 K, and the present results are compared with those obtained previously using the time-of-flight (TOF) technique, on the same compound. In the octahedral sheet, Al tends to order into the M2 site, in accordance with the measurements mentioned above, whereas the Al/Si tetrahedral ordering we observe (i.e. Si fully into T1 site) is at variance with that determined previously. These discrepancies are ascribed to the presence of talc impurities in the sample used previously (~6 wt.%), which affected the results obtained.

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Section: Comparison With Results From Previous Measurementssupporting

confidence: 81%

“…Such constraints are justi®ed by the fact that T1 and T2 (M2 and M3) are expected, on the basis of the results from single crystal XRD studies (Amisano-Canesi et al, 1994), to have similar AtDPs.…”

Section: Site Compositionsmentioning

confidence: 95%

Further study of the cation ordering in phengite 3T by neutron powder diffraction

et al. 2000

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“…Bailey (1984) noted that tetrahedral rotation angles (α) for dioctahedral micas range from about 6 to 19º. The crystal structures of two natural 3T phengitic muscovites have recently been reported by Amisano-Canesi et al (1994). One of these samples (from Dora Maira) contains 11 % Al on the T sites and shows a tetrahedral rotation angle of 5.4º.…”

Section: Introductionmentioning

confidence: 99%

“…After correction for absorption, equivalent reflections were averaged with an R of merging of 0.013 for 2M 1 and 0.008 for the 3T sample. The initial atom positions were those from Comodi & Zanazzi (1995) for 2M 1 and Amisano-Canesi et al (1994) for 3T. The 2M 1 structure was refined in space group C2/c and the 3T in P3 1 12.…”

Section: Introductionmentioning

confidence: 99%

Crystal structures and compressibilities of synthetic 2M1 and 3T phengite micas

Smyth¹,

Jacobsen²,

Swope³

et al. 2000

ejm

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Abstract:The crystal structures of co-existing monoclinic 2M 1 and trigonal 3T polytypes of phengitic micas synthesized at 11 GPa and 900 ºC have been refined at ambient conditions. The compositions of both . The molar volumes of the two polytypes are identical within error (approximately one part in 4000). The structures show closely similar distortions consistent with the nearly pure silicate tetrahedral layer. The tetrahedral rotation angles, α, are both about 2.4º and thus the smallest yet reported for dioctahedral micas. There is no indication of tetrahedral ordering of Al and Si. The 3T polytype contains two distinct octahedral sites that appear to be distinctly different in size indicating possible ordering of Mg and Al. The unit cell parameters of the 2M 1 sample have been measured at several pressures up to 7.5 GPa and those of the 3T sample to 4.0 GPa. Fitting compression data to a third-order Birch-Murnaghan equation of state gives a K 0 of 57 ± 3 GPa with K' of 9.2 ± 1.7 for the 2M 1 and a K 0 of 62 ± 2 GPa with a fixed K' of 9 for the 3T. These are statistically identical and represent the largest bulk modulus yet measured for any mica. As with other micas, compressional anisotropy is large with compression normal to the layers being about seven times that within the layers.

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“…The understanding of the factors responsible for various polytypes in micas is important for field and experimental studies insofar as polytypism is an indicator of the conditions prevailing during petrogenesis. For example, phengitic muscovite favors 3T stacking over 2M 1 stacking at high pressure (Sassi et al 1994;Amisano-Canesi et al 1994;Pavese et al 1997Pavese et al , 1999Pavese et al , 2000.…”

Section: Introductionmentioning

confidence: 99%

Chemical control of 3T stacking order in a Li-poor biotite mica

Fregola

Capitani

Scandale

et al. 2009

American Mineralogist

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The microstructural features of a biotite (Mg-rich annite) crystal from dacite rocks of Džep, Serbia, were studied by X-ray diffraction topography (XRDT) and high-resolution and analytical transmission electron microscopy (HRTEM and ATEM, respectively). The average chemical composition, obtained by electron microprobe analysis (EMPA) and secondary-ion mass spectrometry (SIMS) data, is\ud (K0.87Na0.05Ca0.01)Σ=0.93(Fe2+1.36Mg1.25Ti0.22Al0.14Mn0.03Li0.01)Σ=3.01(Si2.84Al1.16)Σ=4.00O10[(OH)1.53O0.35F0.10Cl0.02]Σ=2.00.\ud Inhomogeneous regions from either different polytypes or twins were mapped by XRDT, and these images were used to guide sampling for TEM analysis. Three stacking arrangements, each belonging to subfamily-A of mica polytypes, were identified by selected area electron diffraction (SAED) patterns\ud and HRTEM images: (1) dominant semi-random 1Mr-n(120°), including an occasional repetition of long-period inhomogeneous stacking sequences belonging to the 3T structural series; (2) highly faulted 2M1, sometimes with short-range-ordered long-period inhomogeneous sequences based on the 2M1 structural series; and (3) perfectly ordered 3T stacking repeating over long distances (several micrometers).\ud ATEM data revealed that the microchemical composition of 3T differs from that of the host matrix. The 3T is enriched in interlayer cations (K and Na), and depleted in Si and octahedral cations. No evidence of Li was detected. Compositional control on the stability of 3T stacking is suggested

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Muscovite- and phengite-3T: crystal structure and conditions of formation

Cited by 38 publications

References 0 publications

Further study of the cation ordering in phengite 3T by neutron powder diffraction

Further study of the cation ordering in phengite 3T by neutron powder diffraction

Crystal structures and compressibilities of synthetic 2M1 and 3T phengite micas

Chemical control of 3T stacking order in a Li-poor biotite mica

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