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Crystal and molecular structure study of garnets from selected localities of the České středohoří Mts.
Píšová, Barbora ; Skála, Roman (advisor) ; Laufek, František (referee)
Major and minor element contents of garnets from mantle peridotites and eclogites brought to the surface by volcanic rocks of the České středohoří Mts. were determined by an electron probe microanalyzer. Garnets are homogenous and their chemical composition corresponds to solid solution containing 65-71 % pyrope, other end members significantly present are almandine, uvarovite and grosulare. This method also help to discover polyphase inclusions chemically corresponding to amphiboles (pargasite, cummingtonite, magnesio-hornblende and katophorite). Next to amphiboles following minerals were found in inclusions: omphacite, carbonates, phlogopite, clinochlore, olivine, apatite, spinel group minerals, and sulfidic phases potentially close to pentlandite. Samples were also analyzed by powder X-ray diffraction. Qualitative phase analysis confirmed pyrope homogeneity. The refinement of crystal structure parameters was performed by the Rietveld method. Raman microspectroscopy showed shifts of individual bands in the Raman spectra compared to those of pure pyrope. Position of bands in spectra differs due to the substitution of Ca for Mg at the dodecahedral sites of the structure. Mutual positive correlations among elements Cr, Ca, Mg, Al, Si, Mn, Ti and Na were observed. Correlations were found also between...
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Crystal chemistry of pyralspite garnets
Soumar, Jan ; Skála, Roman (advisor) ; Ulrych, Jaromír (referee)
Bohemian garnets have been known as a jewellery stone for many centuries. There is still a lot of interest in them, however, the reserves in traditional locations are getting smaller. That is why search for alternative source of similar garnets in gem quality started. Shavaryn Tsaram deposit in Mongolia is considered as one of the potential sources. Pyrope samples from eight Bohemian localities of two areas (České středohoří [The Central Bohemian Uplands] and Podkrkonoší [The Giant Mountains]) and from Shavaryn Tsaram deposit in Mongolia were analysed using electron microprobe, LA-ICP-MS, ICP-OES, Mössbauer spectroscopy and x-ray powder diffraction. The data were compared with the conclusion that the Mongolian garnets from Shavaryn Tsaram deposit are so different from the Bohemian ones that it will not be possible to use them as a gem material of similar qualities. Bohemian garnet can be characterised as a red garnet with refraction index 1.747 (+/- 0.001) with dominant pyrope component of the average composition Py78Alm17Gr5 and Cr2O3 content above 1 wt.%. The data were also evaluated from two classification schemes point of view. The schemes by Schulze (2003) and Grütter (2004) are used in determining source materials and in diamond prospection. According to them source rocks of Bohemian garnets...
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Crystal and molecular structure study of garnets from selected localities of the České středohoří Mts.
Píšová, Barbora ; Skála, Roman (advisor) ; Laufek, František (referee)
Major and minor element contents of garnets from mantle peridotites and eclogites brought to the surface by volcanic rocks of the České středohoří Mts. were determined by an electron probe microanalyzer. Garnets are homogenous and their chemical composition corresponds to solid solution containing 65-71 % pyrope, other end members significantly present are almandine, uvarovite and grosulare. This method also help to discover polyphase inclusions chemically corresponding to amphiboles (pargasite, cummingtonite, magnesio-hornblende and katophorite). Next to amphiboles following minerals were found in inclusions: omphacite, carbonates, phlogopite, clinochlore, olivine, apatite, spinel group minerals, and sulfidic phases potentially close to pentlandite. Samples were also analyzed by powder X-ray diffraction. Qualitative phase analysis confirmed pyrope homogeneity. The refinement of crystal structure parameters was performed by the Rietveld method. Raman microspectroscopy showed shifts of individual bands in the Raman spectra compared to those of pure pyrope. Position of bands in spectra differs due to the substitution of Ca for Mg at the dodecahedral sites of the structure. Mutual positive correlations among elements Cr, Ca, Mg, Al, Si, Mn, Ti and Na were observed. Correlations were found also between...
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Crystal chemistry of pyralspite garnets
Soumar, Jan ; Skála, Roman (advisor) ; Ulrych, Jaromír (referee)
Bohemian garnets have been known as a jewellery stone for many centuries. There is still a lot of interest in them, however, the reserves in traditional locations are getting smaller. That is why search for alternative source of similar garnets in gem quality started. Shavaryn Tsaram deposit in Mongolia is considered as one of the potential sources. Pyrope samples from eight Bohemian localities of two areas (České středohoří [The Central Bohemian Uplands] and Podkrkonoší [The Giant Mountains]) and from Shavaryn Tsaram deposit in Mongolia were analysed using electron microprobe, LA-ICP-MS, ICP-OES, Mössbauer spectroscopy and x-ray powder diffraction. The data were compared with the conclusion that the Mongolian garnets from Shavaryn Tsaram deposit are so different from the Bohemian ones that it will not be possible to use them as a gem material of similar qualities. Bohemian garnet can be characterised as a red garnet with refraction index 1.747 (+/- 0.001) with dominant pyrope component of the average composition Py78Alm17Gr5 and Cr2O3 content above 1 wt.%. The data were also evaluated from two classification schemes point of view. The schemes by Schulze (2003) and Grütter (2004) are used in determining source materials and in diamond prospection. According to them source rocks of Bohemian garnets...
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