Thermochemistry of guest-free melanophlogite

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doi: 10.2138/am-2003-1026
Authors:Navrotsky, Alexandra; Xu, Hongwu; Moloy, Eric C.; Welch, Mark D.
Author Affiliations:Primary:
University of California at Davis, Thermochemistry Facility and NEAT ORU, Davis, CA, United States
Other:
Natural History Museum, United Kingdom
Volume Title:American Mineralogist
Source:American Mineralogist, 88(10), p.1612-1614. Publisher: Mineralogical Society of America, Washington, DC, United States. ISSN: 0003-004X
Publication Date:2003
Note:In English. 11 refs.; illus.
Summary:Melanophlogite is a naturally occurring clathrasil possessing a framework of linked silicate tetrahedra surrounding small, isolated cages, which can host small molecules. The energetics of a guest-free natural sample was determined by oxide-melt solution calorimetry. Melanophlogite is energetically metastable with respect to α-quartz by 9.5±0.5 kJ/mol, a value similar to that for amorphous silica and for synthetic small-pore zeolitic silicas (Petrovic et al. 1993, Piccione et al. 2001). Thus, its occurrence in nature, for example in environments/where it can occlude volcanic gases, is reasonable on energetic grounds. Molecular modeling of the internal pore volume of melanophlogite confirms that this enthalpy follows the trend previously established for a variety of silica zeolites, which defines an internal surface energy of 0.093±0.010 J/m2, similar to that of the external surface energy of amorphous silica. Thus melanophlogite, despite its unique topology and isolated cages, behaves energetically as predicted from the enthalpies of more-open zeolitic frameworks.
Sections:Experimental mineralogy
Subsections:Silicates
Subjects:Calorimetry; Crystal chemistry; Enthalpy; Framework silicates; High temperature; Melanophlogite; NMR spectra; Silica minerals; Silicates; Spectra; Temperature; Thermochemical properties
Abstract Numbers:04M/2196
Record ID:2004001419
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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