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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]
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.
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 ...
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]
Two recognized types of intraformational conglomerates are shale-pebble and flat-pebble conglomerates. [6] A shale-pebble conglomerate is a conglomerate that is composed largely of clasts of rounded mud chips and pebbles held together by clay minerals and created by erosion within environments such as within a river channel or along a lake ...
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.
Since the nature of cleavage is dependent on scale, slaty cleavage is defined as having 0.01 mm or less of space occurring between layers. [1] Slaty cleavage often occurs after diagenesis and is the first cleavage feature to form after deformation begins. The tectonic strain must be enough to allow a new strong foliation to form, i.e. slaty ...
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. [1] The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram in Figure 1). [1]