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Greywacke

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About GreywackeHide

A wacke generally consisting of poorly sorted angular grains of quartz, feldspar and lithic fragments set in a compact clay-rich matrix. It is commonly formed from sediment deposited in submarine avalanches or from strong turbidity currents creating mixed-sediment slurries. They are often found on the edges of continental shelves or at the bottom of oceanic trenches. An old rock name that has been variously defined but is now generally applied to a dark gray, firmly indurated, coarse-grained sandstone that consists of poorly sorted, angular to subangular grains of quartz and feldspar, with a variety of dark rock and mineral fragments embedded in a compact clayey matrix having the general composition of slate and containing an abundance of very fine-grained illite/sericite, and chlorite. Graywacke is abundant within the sedimentary section, esp. in the older strata, usually occurring as thick, extensive bodies with sole marks of various kinds and exhibiting massive or obscure stratification in the thicker units but marked graded bedding in the thinner layers. It generally reflects an environment in which erosion, transportation, deposition, and burial were so rapid that complete chemical weathering did not occur, as in an orogenic belt where sediments derived from recently elevated source areas were poured into a geosyncline. Graywackes are typically interbedded with marine shales or slates, and associated with submarine lava flows and bedded cherts; they are generally of marine origin and are believed to have been deposited by submarine turbidity currents. Also spelled: graywacke; grauwacke.

Compare with: arkose, subgraywacke

Ref: AGI


Classification of GreywackeHide

Mineralogy of GreywackeHide

Essential minerals - these are minerals that are required within the classification of this rock:
FeldsparA petrological term for Feldspar Group.
Silica > QuartzSiO2
Non-essential minerals - these minerals are common, sometimes major components, but are not always present:
Amphibole > HornblendeAn informal name for dark green to black amphiboles, mostly ferro-hornblende or ...
Apatite"Apatite" is a field term for unidentified calcium phosphate members of the apatite group.
CalciteCaCO3
ChloriteA name commonly used for undifferentiated members of the chlorite group.
Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Garnet GroupX3Z2(SiO4)3
Mica > BiotiteA series or subgroup of the Mica Group.
PyriteFeS2
Pyroxene > Clinopyroxene > Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
TitaniteCaTi(SiO4)O
TourmalineA(D3)G6(T6O18)(BO3)3X3Z

Synonyms of GreywackeHide

Internet Links for GreywackeHide

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