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Cleavage forms parallel to crystallographic planes: [1] Basal, pinacoidal, or planar cleavage occurs when there is only one cleavage plane. Talc has basal cleavage. Mica (like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets. Prismatic cleavage occurs when there are two cleavage planes in a crystal ...
This characteristic is described as perfect basal cleavage. Mica is common in igneous and metamorphic rock and is occasionally found as small flakes in sedimentary rock. [6] It is particularly prominent in many granites, pegmatites, and schists, [7] and "books" (large individual crystals) of mica several feet across have been found in some ...
Muscovite (also known as common mica, isinglass, or potash mica [6]) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl 2 (AlSi 3 O 10)(F,OH) 2, or 2 (Al 2 O 3) 3 (SiO 2) 6 (H 2 O). It has a highly perfect basal cleavage yielding remarkably thin laminae (sheets) which are often highly elastic.
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 ...
Grains of platy minerals, such as clay minerals, are rotated to form parallel layers perpendicular to the direction of compaction, which begin to impart cleavage to the rock. Slaty cleavage is fully developed as the clay minerals begin to be converted to chlorite and mica. Organic carbon in the rock is converted to graphite. [11]
Like other mica minerals, biotite has a highly perfect basal cleavage, and consists of flexible sheets, or lamellae, which easily flake off. It has a monoclinic crystal system, with tabular to prismatic crystals with an obvious pinacoid termination. It has four prism faces and two pinacoid faces to form a pseudohexagonal crystal. Although not ...
This is related to the axis of folds, which generally form an axial-planar foliation within their axial regions. Measurement of the intersection between a fold's axial plane and a surface on the fold will provide the fold plunge. If a foliation does not match the observed plunge of a fold, it is likely associated with a different deformation event.
Fuchsite, also known as chrome mica, is a chromium (Cr)-rich variety of the mineral muscovite, belonging to the mica group of phyllosilicate minerals, with the chemical formula K(Al,Cr) 3 Si 3 O 10 (OH) 2. [2] Trivalent chromium replaces one of the aluminium (Al) atoms in the general muscovite formula producing the apple green hue distinctive ...