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@article{1748896,
author = {Koníčková, Šárka and Losos, Zdeněk and Houzar, Stanislav and Všianský, Dalibor},
article_location = {Bratislava},
article_number = {1},
doi = {http://dx.doi.org/10.31577/GeolCarp.72.1.5},
keywords = {Bohemian Massif; Carpathian Foredeep; paleo-weathering; Miocene sediment-serpentinite interaction; green zonal silica nodule},
language = {eng},
issn = {1335-0552},
journal = {Geologica Carpathica},
title = {Specific green zonal silica nodules of serpentinite weathering: Unusual products of silicification in laterite-like residuum (Moldanubian Zone, Bohemian Massif)},
url = {http://www.geologicacarpathica.com/browse-journal/volumes/72-1/article-970/},
volume = {72},
year = {2021}
}
TY - JOUR
ID - 1748896
AU - Koníčková, Šárka - Losos, Zdeněk - Houzar, Stanislav - Všianský, Dalibor
PY - 2021
TI - Specific green zonal silica nodules of serpentinite weathering: Unusual products of silicification in laterite-like residuum (Moldanubian Zone, Bohemian Massif)
JF - Geologica Carpathica
VL - 72
IS - 1
SP - 68-81
EP - 68-81
PB - Earth Science Institute of the Slovak Academy of Sciences
SN - 13350552
KW - Bohemian Massif
KW - Carpathian Foredeep
KW - paleo-weathering
KW - Miocene sediment-serpentinite interaction
KW - green zonal silica nodule
UR - http://www.geologicacarpathica.com/browse-journal/volumes/72-1/article-970/
N2 - Massive quartz-chakedony +/- opal nodules ("plasma" in gemology) represent a specific silica variety, which occurs in the laterite-like residues of pre-Miocene paleo-weathering of ultramafites in western Moravia (Moldanubian Zone, Bohemian Massit). These zonal silica nodules (ZSN) tend to have concentric texture with a dark green to green-brown core, pale green margin and a narrow white rim (outer surface zone). The most typical microscopic feature of ZSN is vermiform microstructure particularly in the two outer zones. Individual mines consist of micro- to non-crystalline SiO2 polymorphs with variable contents of H2O (quartz, chalcedony, moganite, opal-C/CT and opal-A). The predominant green colour is due to submicroscopic smectite pigment, while the brownish colour originated from decomposition of smectite to iron oxohydroxides. ZSN formed in subaerial, partially reducing conditions in the lower part of weathering crusts covering serpentinites. The whole process was preceded by component exchange (chloritization) along serpentinite -felsic rocks (granulite. migmatite, pegmatite veins) boundaries. The gradual silica migration and subsequent redistribution associated with the removal of aluminium, magnesium and iron led up to the formation of a zonal nodular texture dominated by SiO2 polymorphs. Newly formed minerals in micro-cavities and cracks of ZSN are represented by accessory pyrite and sporadic barite. Zonal silica nodules-bearing residues on serpentinites occur only in a narrow area which was originally covered by clay-sandy Miocene sediments of the Carpathian Foredeep in western Moravia. Probably late low-temperature fluid interaction between silicified serpentinite residuum (chlorite montmorillonite saprolite) and marine sediments may be the main factor controlling formation of ZSN.
ER -
KONÍČKOVÁ, Šárka, Zdeněk LOSOS, Stanislav HOUZAR and Dalibor VŠIANSKÝ. Specific green zonal silica nodules of serpentinite weathering: Unusual products of silicification in laterite-like residuum (Moldanubian Zone, Bohemian Massif). \textit{Geologica Carpathica}. Bratislava: Earth Science Institute of the Slovak Academy of Sciences, 2021, vol.~72, No~1, p.~68-81. ISSN~1335-0552. Available from: https://dx.doi.org/10.31577/GeolCarp.72.1.5.
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