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Hollandit a kryptomelan z Poniklé u Jilemnice, Česká republika

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    0451735 - ÚGN 2016 RIV CZ eng J - Journal Article
    Jirásek, J. - Matýsek, D. - Vaculíková, Lenka - Sivek, M.
    Hollandit a kryptomelan z Poniklé u Jilemnice, Česká republika.
    Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze. -, č. 23 (2015), s. 1-6. ISSN 1211-0329
    R&D Projects: GA MŠMT ED2.1.00/03.0082; GA MŠMT(CZ) LO1406
    Institutional support: RVO:68145535
    Keywords : hollandite supergroup * coronadite group * mineralogy * infrared spectroscopy * Poniklá Group
    Subject RIV: DB - Geology ; Mineralogy

    At historical iron ore mining site near Poniklá, famous for natrodufrénite occurence, were described two minerals from the coronadite group (hollandite supergroup) - hollandite and cryptomelane. They are present in cavities and fissures of brecciated iron ore with quartz. Both form of greyish-black to black reniform aggregates with dull to sub¬metallic lustre several milimeters thick, covering the areas mostly up to 10 cm2. Submicroscopic layers of hollandite are alternating with the same of cryptomelane. Occurence of minerals from coronadite group was confirmed by the powder XRD, as well as by IRS. Chemical data from EMPA-WDS confirmed presence of both phases with composition close to its end-members, with minor admixture of Ca2+, Sr2+ a Fe3+, in case of hollandite also K+. We believe that these minerals were originally described as psilomelane and pyrolusite in 19th century from the Poniklá. Co-existence of iron and manganese oxidic minerals well corresponds to iron-rich residual deposits, where both elements remain fixed in relatively stable minerals and their mobility remains unimportant even during lateritic weathering and carst formation.
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