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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 .
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 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.
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 ...
The pegmatites and country rock are part of the Spruce Pine thrust block, the highest thrust sheet of the Blue Ridge belt, the latter being part of the Tugaloo Terrane which was accreted to North America during the Taconic Orogeny. [2] A more refined age for the pegmatites within the district has been found through 40 Ar/ 39 Ar dating
Similar to nearby Horsetooth Mountain, Arthur's Rock is composed of 1.7 billion year-old pegmatite, a type of intrusive igneous rock.. The rock that now forms the summit was originally a subterranean pluton, a part of the wider Log Cabin Batholith that covers much of the area currently.
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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.