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München, Germany

Hochleitner R.,Mineralogical State Collection | Fehr K.T.,Section Mineralogy
Canadian Mineralogist | Year: 2010

Keckite is considered to be a member of the jahnsite group, though the formula originally given does not conform to the general formula of minerals of that group. In this study, samples of keckite from different localities, including the type locality, have been investigated. Keckite is a special member of the jahnsite group containing trivalent iron not only at the C site but also at the B site, as proven by Mössbauer spectroscopy. The chemical composition was determined by electron-microprobe analysis, and the H 2O content, by differential thermogravimetry. A new formula for keckite is proposed: CaMn(Fe 3+,Mn) 2 Fe 3+ 2(OH) 3(H 2O) 7[PO 4] 4. Source


Buikin A.I.,University of Heidelberg | Buikin A.I.,RAS Vernadsky Institute of Geochemistry and Analytical Chemistry | Trieloff M.,University of Heidelberg | Korochantseva E.V.,University of Heidelberg | And 5 more authors.
Journal of Petrology | Year: 2010

To investigate the geochemical behaviour of argon isotopes during mantle metasomatism and to obtain chronological information on the age of metasomatic events under the Arabian Shield, we analyzed mantle xenoliths and hornblende megacrysts from Saudi Arabian volcanic fields (Uwayrid, Al Birk) applying the 40Ar-39Ar dating technique. Two hornblende megacrysts yield plateau ages indicating formation or total resetting of the K/Ar system 1-2 Myr ago. The ultramafic xenoliths trapped mantle-derived and atmospheric argon in different proportions, resulting in variable isotopic compositions: 40Ar/36Ar ratios range from 296 (i.e. atmospheric) to ~10 500, reflecting interactions with isotopically and genetically different fluids and/or melts during recent mantle metasomatism. One such episode of metasomatism led to the formation of Ba-rich phlogopite, which yielded a saddle-shaped age spectrum with a maximum age estimate of ~18 Ma. Another episode, inducing formation of secondary pargasite in the lithospheric mantle, was dated to ~4 Ma. In the mantle xenoliths the concentration of mantle argon is clearly related to the intensity of metasomatism. Argon extraction by high-resolution stepwise heating allowed us to deconvolve various argon components distributed heterogeneously within single xenoliths and ascribe them to specific carrier phases. Pyroxenes generally preserve much higher 40Ar/36Ar ratios than olivine, as they contain up to 100 times higher concentrations of mantle argon, which also correlates with a higher fluid inclusion content in pyroxenes. Hydrous phases (phlogopite/amphibole) have more variable 40Ar/36Ar ratios. K and Cl concentrations and the argon isotope compositions of the Uwayrid xenoliths indicate distinct metasomatic agents, causing elemental and isotopic disequilibrium on a local scale. On the basis of correlations between Ar isotope composition and K and Cl concentration in the samples most strongly affected by the late metasomatic fluids, we suggest that metasomatic processes in the local mantle occurring simultaneously with the opening of the Red Sea were accompanied by the introduction of saline-water saturated fluids into deep lithospheric zones. © The Author 2010. Published by Oxford University Press. All rights reserved. Source


Kaliwoda M.,Mineralogical State Collection | Hochleitner R.,Mineralogical State Collection | Hoffmann V.H.,Ludwig Maximilians University of Munich | Mikouchi T.,University of Tokyo | And 2 more authors.
Spectroscopy Letters | Year: 2013

Raman spectroscopy is a convenient method to classify polytypes plus polymorphs and to investigate different compositions, structures, and modifications of minerals. This information is required to classify meteorites of different mineral compositions. Our intention was to examine different graphite modifications and to determine the opaque phases within the Almahatta Sitta (AS) meteorite. Our investigation focused on specimens AS39 and AS4. Both are multicomponent breccias, composed of different meteoritic lithologies, that is, anomalous polymict ureilite material, different types of chondrites, and an iron meteorite.[ 1-5 ] The mix of material implicates a crash of variable asteroids within time and space. This means that a primary ureilitic asteroid body has been the target of multiple meteorite or asteroid impacts, which did not completely destroy the asteroid but added new material (from chondritic to iron) to the main mass. For instance, Gabriel and Pack [ 6 ] suggested that the vein metal of monomict ureilites is introduced by the impact of a Ni-poor iron meteorite in a similar scenario as described above. Raman spectroscopy helped to investigate different carbon materials, that is, graphite and diamond. We used single-spectrum acquisition and spatial mappings to identify the different modifications. Furthermore, we classified minor opaque phases such as schreibersite, suessite, daubreelite, cohenite, and kamacite. The investigation of these opaque phases is dealt with in further papers.[1,2] © 2013 Copyright Taylor and Francis Group, LLC. Source


Hoffmann V.H.,Ludwig Maximilians University of Munich | Hoffmann V.H.,University of Tubingen | Hochleitner R.,Mineralogical State Collection | Torii M.,Okayama University of Science | And 5 more authors.
Meteoritics and Planetary Science | Year: 2011

The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC3 consortium were investigating Almahata Sitta's (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009). © The Meteoritical Society, 2011. Source


Bauer M.,Ludwig Maximilians University of Munich | Bauer M.,Center for Nanoscience | Davydovskaya P.,Ludwig Maximilians University of Munich | Davydovskaya P.,Center for Nanoscience | And 7 more authors.
Journal of Raman Spectroscopy | Year: 2011

Titanomagnetites are important carriers of magnetic remanence in nature and can track redox conditions in magma. The titanium concentration in magnetite bears heavily on its magnetic properties, such as saturation moment and Curie temperature. On land and in the deep ocean, however, these minerals are prone to alteration which can mask the primary magnetic signals they once recorded. Thus, it is essential to characterize the cation composition and oxidation state of titanomagnetites that record the paleomagnetic field. Raman spectroscopy provides a unique tool for both purposes. Nonetheless, the heat generated by the excitation laser can itself induce oxidation. We show that the laser power threshold to produce oxidation decreases with increasing titanium content. With confocal Raman spectroscopy and magnetic force microscopy (MFM) on natural and synthetic titanomagnetites, a non-destructive Raman imaging protocol was established. We applied this protocol to map out the composition and magnetization state within a single ex-solved titanomagnetite grain in a deep-sea basalt. Copyright © 2011 John Wiley & Sons, Ltd. Source

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