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Characteristics and origin of agates from Płóczki Górne (Lower Silesia, Poland): A combined microscopic, micro-Raman, and cathodoluminescence study

Agates from Płóczki Górne hosted by Permian basaltic rocks are predominantly made of length-fast chalcedony, and subordinately megaquartz and quartzine. Moganite occurs in traces mainly in transparent, outer, darker regions of white-grey coloured agates. Silica matrix of agates comprises a wide vari...

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Published in:Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2018-03, Vol.192, p.6-15
Main Authors: Dumańska-Słowik, Magdalena, Powolny, Tomasz, Sikorska-Jaworowska, Magdalena, Gaweł, Adam, Kogut, Lucyna, Poloński, Krzysztof
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Language:English
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Summary:Agates from Płóczki Górne hosted by Permian basaltic rocks are predominantly made of length-fast chalcedony, and subordinately megaquartz and quartzine. Moganite occurs in traces mainly in transparent, outer, darker regions of white-grey coloured agates. Silica matrix of agates comprises a wide variety of solid inclusions represented by celadonite, plagioclases, hematite, goethite, barite, calcite, heulandite-clinoptyloite, nontronite-saponite, and Mn-dioxides (ramsdellite). Mineral phases are locally accompanied by black aggregations of carbonaceous matter, which gives a Raman signature of disordered carbon. These organic components were probably deposited from a hydrothermal fluids at low-temperature conditions and originated from sedimentary rocks found in the surrounding area of Płóczki Górne. The abundance of various SiO2 phases, mineral inclusions as well as various micro-textures (colloform, comb, feathery, and jigsaw-puzzle) in agates resulted from physicochemical fluctuations of SiO2-bearing mineralizing solutions at various stages of these gems formation. Agates from Płóczki Górne formed during post-magmatic stage of basaltic host rocks evolution. Not only were the hydrothermal fluids enriched in silica, but also they contained other elements such as Na, Ca, Al, Mg, Mn, Fe, Ba, SO4, and CO2, which were mobilized from host rocks or surrounding area. [Display omitted] •Agates contain chalcedonite, quartzine, megaquartz and traces of moganite.•Permian agates from Płoczki Górne host numerous solid inclusions.•Inclusions are markers of time-varying composition of the mineralizing solutions.•Agates formed under medium to low-temperature hydrothermal conditions.•Recrystallization of pre-existing silica phases took place.
ISSN:1386-1425
DOI:10.1016/j.saa.2017.11.005