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Crystal chemistry of minerals

English title Crystal chemistry of minerals
Applicant Armbruster Thomas
Number 112198
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Mineralogy
Start/End 01.06.2006 - 30.11.2008
Approved amount 164'162.00
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Keywords (7)

crystal structure; minerals; zeolites; cation exchange; crystal chemistry; X-ray diffraction; crystallography

Lay Summary (English)

Lead
Lay summary
a) Microporous materialsTwo classes of microporous materials with important applications in the field of ion exchangers, molecular sieves and catalysts are investigated. (1) Natural zeolites are low cost framework silicates composed of SiO4 and AlO4 tetrahedra with open cavities connected by penetrable channels. Exchangeable cations balance the charge deficit of the framework. Dehydration behavior and structural resistance are studied by temperature dependent X-ray diffraction. All investigated zeolites originate from Bulgarian deposits. The project contributes to pollution abatement in Bulgaria where such zeolites may be applied for extraction of toxic and radioactive (137Cs and 90Sr) ions. (2) Microporous titano- and zirconosilicates represent a relatively new class of zeotype materials with a structural framework constructed of condensed (Ti,Zr)O6 octahedra and SiO4 tetrahedra. Extraframework cations in the microporous interspace can be exchanged as in case of conventional zeolites. Natural single crystals will structurally be analyzed and compared with available synthetic analogues. In addition structure refinements of cation exchanged forms are conducted under ambient conditions and elevated temperature to monitor dehydration, framework distortion, cation diffusion, and possible phase transition. In situ high-pressure experiments are accompanied by X-ray structure study to investigate pressure dependence of framework stability.b) Rockforming mineralsEpidote-group mineralsTawmawite, Ca2Al2Cr3+[Si2O7][SiO4]O(OH), and mukhinite, Ca2Al2V3+[Si2O7][SiO4]O(OH) are old mineral species lacking structural analysis. Independent mineral names are only justified if Cr and V are ordered on one of the three available octahedral sites. Both minerals are oscillatory zoned requiring special preparation techniques to excavate chemically homogeneous fragments from microscopic thin-sections to be studied by state of the art single-crystal X-ray methods.Monoclinic epidote group minerals are investigated by both single-crystal and powder X-ray diffraction. A comparison of refined site occupancies should indicate whether the Rietveld powder technique is an appropriate tool to obtain reliable information on cation site- preference for low symmetry minerals with pronounced reflection overlap in the X-ray diffraction pattern.c) Structural characterization of new minerals The structural and chemical characterization of new minerals complements our knowledge of the earth crust and adds information on the chemical flexibility of certain structure types.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

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Associated projects

Number Title Start Funding scheme
121290 Accessories to single-crystal X-ray equipment 01.07.2008 R'EQUIP
122122 Crystal chemistry of minerals 01.12.2008 Project funding (Div. I-III)
101474 Crystal chemistry of minerals 01.10.2003 Project funding (Div. I-III)

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