Mineralogy of "eye-like" opals from Nová Ves near Oslavany (Moldanubian zone, Bohemian Massif)

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Authors

KONÍČKOVÁ Šárka LOSOS Zdeněk HRAZDIL Vladimír HOUZAR Stanislav VŠIANSKÝ Dalibor

Type Conference abstract
MU Faculty or unit

Faculty of Science

Citation
Description The locality Nová Ves near Oslavany, situated in Moldanubian zone of western Moravia, represents the only known occurrence of zonal "eye-like" (concentric) opals in Bohemian Massif. This specific type of opal is characterized by a concentric zonal texture with white core ("eye"), brown massive translucent inner rim and locally also white porous outer rim. These opals occur in residual sediments in a small area along the contact of serpentinized peridotite and granulite. White and grey "eye" and brown inner zone contains mainly opal-CT. Quartz and moganite are present in part in white aggregates of the "eye" only. White outer rim of opals is composed of calcite with disseminated opal relics and this zone is younger as core and inner rim (calcite replaces opal). X-ray powder diffraction analyses proved presence of sepiolite admixture in brown part and accessory amount of sepiolite and chlorite in white rim.