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The Lewisian gneiss is found throughout the Outer Hebrides of Scotland, on the Scottish mainland west of the Moine Thrust, and on the islands of Coll and Tiree. [20] These rocks are largely igneous in origin, mixed with metamorphosed marble , quartzite and mica schist with later intrusions of basaltic dikes and granite magma.
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin, Al 2 Si 2 O 5 4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. [1]
Cambrian conglomerate, limestone and Alum shale B, lying unconformably above Precambrian gneiss D, intruded by a Permian lamprophyre sill A, Slemmestad, western Oslofjord The early Palaeozoic history of Norway is recorded in sequences preserved either as autochthon or at various levels within the allochthon.
Gneiss, a foliated metamorphic rock. Quartzite, a non-foliated metamorphic rock. Foliation in geology refers to repetitive layering in metamorphic rocks. [1] Each layer can be as thin as a sheet of paper, or over a meter in thickness. [1] The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure. [1]
Hall found that this produced a material strongly resembling marble, rather than the usual quicklime produced by heating of chalk in the open air. French geologists subsequently added metasomatism, the circulation of fluids through buried rock, to the list of processes that help bring about metamorphism. However, metamorphism can take place ...
For hundreds of a millions of years, the universe existed in the dark ages—an epoch when only primordial gasses existed. Then, a period of reionization, cleared away this foggy existence an ...
Foliation develops when a rock is being shortened along one axis during recrystallization. This causes crystals of platy minerals, such as mica and chlorite, to become rotated such that their short axes are parallel to the direction of shortening. This results in a banded, or foliated, rock, with the bands showing the colors of the minerals ...
Scientists say they've discovered a new galaxy that's so dark and compact, it's basically invisible. But it's actually been here the whole time.