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Schist metamorphosed from mudstone is particularly common and is often very rich in mica (a mica schist). Where the type of the original rock (the protolith ) is discernible, the schist is usually given a name reflecting its protolith, such as schistose metasandstone .
Flake mica comes from several sources: the metamorphic rock called schist as a byproduct of processing feldspar and kaolin resources, from placer deposits, and pegmatites. Sheet mica is considerably less abundant than flake and scrap mica, and is occasionally recovered from mining scrap and flake mica.
The natural condition for the quernstone and millstone production in the area is the rock type garnet mica schist. The quarries are located from the shoreline up until approx. 200 m above sea level, but a majority is situated less than one kilometer from the sea and closest harbor.
Metamorphic rock formed in these settings tends to shown well-developed foliation. [33] Foliation develops when a rock is being shortened along one axis during metamorphism. 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 ...
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]
The Wissahickon is described as a pelitic schist and gneiss with interlayers of quartzite. Color is highly variable as is the mineralogy. [2] A general description for the unit is a silver to brown garnet mica-schist.
The dominant bedrock of Mt. Mansfield is a mica-albite-quartz schist common to the Green Mountains, with mica being the most abundant mineral. [10] [11] Layers of quartzite are found locally. [12]
The pointed mica-schist summit of Djouce (left) contrasts with the rounded granite summit of War Hill (right) The Wicklow Mountains are primarily composed of granite surrounded by an envelope of mica-schist and much older rocks such as quartzite.