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A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite.
This is typical of pegmatites. Pegmatites are most commonly formed as coarse-grained igneous rocks of granitic composition, containing large clasts of gemstones such as amazonite, garnet, and topaz. Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface.
The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
Greisen is a highly altered granitic rock or pegmatite, usually composed predominantly of quartz and micas (mostly muscovite). Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic-hydrothermal alteration related to the late-stage release of volatiles dissolved in a magma during the ...
Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. Typically, the pure potassium endmember of orthoclase forms a solid solution with albite , the sodium endmember (NaAlSi 3 O 8 ), of plagioclase .
If the pegmatite fluid is rich in beryllium, crystals of beryl or chrysoberyl could form. Beryl has a high ratio of beryllium to aluminium, while the opposite is true for chrysoberyl. Both are stable with the common mineral quartz. For alexandrite to form, some chromium would also have had to be present. However, beryllium and chromium do not ...
The Tin Mountain pegmatite is roughly L-shaped, with the longer leg trending N7’W and the other trending N75’W. [2] It is approximately 200 m long and is 30 m wide at the maximum. [3] It is a vertically differentiated zoned pegmatite, and consists of five main zones: the wall zone, three intermediate zones, and a core.
Manganocolumbite is often found in pegmatites, course-grained igneous rocks. [15] Ferrocolumbite; a species of columbite. The iron-rich member of the columbite group is ferrocolumbite, FeNb 2 O 6, and small concentrations of tin and tungsten may be present. This species of columbite is often found in pegmatites as course-grained igneous rocks. [15]