The heat capacity of the serpentine subgroup mineral berthierine (Fe2.5Al0.5) Si1.5Al0.5O5 (OH)(4)

Bertoldi, C., Dachs, E., Cemic, L., Theye, T., Wirth, R. and Groger, W. (2005) The heat capacity of the serpentine subgroup mineral berthierine (Fe2.5Al0.5) Si1.5Al0.5O5 (OH)(4) Clays and Clay Minerals, 53 (4). pp. 380-388. DOI 10.1346/ccmn.2005.0530406.

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The serpentine subgroup mineral berthierine was synthesized as a metastable precursor of the chlorite group mineral chamosite in cold seal pressure vessels at 575 degrees C, 0.5 GPa and f(O2) -conditions of the NNO buffer from a glass of almandine bulk composition. The run products were investigated with X-ray powder diffraction (XRD), Mossbauer spectroscopy and electron microprobe analysis. One run product was also investigated by high-resolution transmission electron microscopy (HRTEM) and its heat capacity measured by heat pulse calorimetry and by differential scanning calorimetry in the temperature range 5-323 K. TheXRD and HRTEM investigations clearly showed that the periodicity along the e axis of this sample is 7 A demonstrating that the serpentine subgroup mineral berthierine of composition (Fe1832+Fe0.333+Al0.67)-Fe-.)[Si1.33Al0.67O5](OH)(4) has formed in the synthesis experiments. Integration of our heat capacity data, corrected to the composition (Fe2.5Al0.5)[Si1.5Al0.5O5](OH)(4) for end-member berthicrine, yields a standard entropy of 284.1 +/- 0.3 J mol(-1) K-1. The C-p polynomial C-p = 610.72 - 5140.0 x T-0.5 - 5.8848 x 10(6) T-2 + 9,5444 x 10(8) T-3 is recommended for thermodynamic calculations above 298 K involving berthierine.

Document Type: Article
Keywords: berthierine differential scanning calorimetry heat capacity heat-pulse calorimetry serpentine subgroup minerals standard entropy differential scanning calorimetry grain-coating chlorite sandstones stability verdine facies origin annite model
Research affiliation: Kiel University
DOI etc.: 10.1346/ccmn.2005.0530406
ISSN: 0009-8604
Date Deposited: 18 Jan 2012 05:11
Last Modified: 08 Oct 2012 10:26

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