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Gneiss

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A medium to high grade metamorphic rock that commonly has a banded structure that are generally medium to coarse grained with poorly developed schistosity.
A foliated rock formed by regional metamorphism, in which bands or lenticles of granular minerals alternate with bands or lenticles in which minerals having flaky or elongate prismatic habits predominate. Generally less than 50% of the minerals show preferred parallel orientation. Although a gneiss is commonly feldspar- and quartz-rich, the mineral composition is not an essential factor in its definition. Varieties are distinguished by texture (e.g., augen gneiss), characteristic minerals (e.g., hornblende gneiss), or general composition and/or origins (e.g., granite gneiss).


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Classification of GneissHide

RockMetamorphic rockGneiss

Sub-divisions of GneissHide

Mineralogy of GneissHide

Non-essential minerals - these minerals are common, sometimes major components, but are not always present:
AmphiboleAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
FeldsparA petrological term for Feldspar Group.
MicaA petrological term for Mica Group.
Silica > QuartzSiO2

Pronounciation of GneissHide

Pronounciation:
PlayRecorded byCountry
Jolyon & Katya RalphUnited Kingdom

Age informationHide

Age range:
Devonian : 419.2 ± 3.2 Ma to 358.9 ± 0.4 Ma - based on data given below.
Sample ages:
Sample IDRecorded ageGeologic TimeDating method
1419.2 ± 3.2 to 358.9 ± 0.4 MaDevonian
Sample references:
IDLocalityReference
1Lizard Complex, Lizard Peninsula, Cornwall, England, UKStyles, M. T., Cook, C. A., & Holdsworth, R. E. (2000). The geology of the Lizard Complex; 100 years of progress. Geoscience in South West England, 10(1), 092-098.

Internet Links for GneissHide

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