Term
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Definition
Alkali feldspar >2/3 total feldspar
Quartz >10%
CI 10
Chiefly horneblende, biotite, pyroxene, muscovite
Volcanic: Rhyolite
Plutonic: Granite |
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Term
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Definition
Alkali feldspar 1/3-2/3 totatl feldspar
Quartz >10%
CI 20
Chiefly hornblende, biotite, pyroxene
Volcanic: Quartz latite
Plutonic: Adamellite, Quartz Monzonite |
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Term
| Plagioclase Feldspar Rocks 1 |
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Definition
Plagioclase feldspar >2/3 total feldspar
Quartz >10%
Alkali feldspar >10% total feldspar
CI 20
Chiefly hornblende, biotite, pyroxene
Volcanic: Dacite
Plutonic: Granodiorite |
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Term
| Plagioclase Feldspar Rocks 2 |
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Definition
Plagioclase feldspar >2/3 total feldspar
Quartz >10%
Sodic plagioclse
CI 20
Chiefly hornblende, biotite, pyroxene
Volcanic: Dacite
Plutonic: Tonalite |
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Term
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Definition
| Extrusive, holocrystalline to hypocrystalline, with aphanitic groundmass. Mineral composition similar to granite. Alkali feldspar generally exceeds plagioclase. Two main types of rhyolites - potassic (most common), and sodic |
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Term
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Definition
| Rhyolites characterized by alkali pyroxenes and amphiboles. |
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Term
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Definition
| Natural glass of rhylitic composition. Phenocrysts are rare, crystallites are common. |
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Term
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Definition
| Glassy igneous rock that differs from obsidian in being less vitreous and more pitch-like in luster. In general contains more water (up to 10%) than obsidian (<4%) |
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Term
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Definition
| Extrusive, holocrystalline to hypocrystalline, uncommonly vitreous, with aphanitic groundmass. Usually porphyritic. Volcanic equivalent of granodiorite and tonalite. Phenocrysts of plagioclase +- quartz +- biotite +- amphibole +- pyroxene. |
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Term
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Definition
| Extrusive equivalent of grodiorite. Porphyritic with phenocrysts of plagioclase (oligoclase-andesine) +- sanidine or anorthoclase and mafic minerals (hornblende, biotite, occasionally augite). |
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Term
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Definition
| Coarse-grained plutonic rock containing >20% quartz, alkali feldspar is >35% of total feldspar, mafics 10-35% (biotite, hornblende, alkali amphiboles) |
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Term
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Definition
Perthitic orthoclase or microcline
Oligioclase
Biotite +- muscovite
Hornblende
Diopside or augite |
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Term
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Definition
Strongly perthitic orthoclase or microcline
Albite or Na oligoclase
Fe-rich biotite
Alkali amphiboles
Alkali pyroxenes |
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Term
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Definition
| Fine to medium-grained rocks having groundmass feldspar and quartz in micrographic intergrowth. Less common rocks of granite family. |
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Term
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Definition
| Fine-grained, light-colored rocks with an even grain size that rarely exceeds 2 mm. In hand specimen they appear sugary. Rich in quartz, alkali feldspar, muscovite, and pneumatolic minerals. |
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Term
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Definition
| Coarse-grained light colored rocks. Principally composed of quartz, alkali feldspar and muscovite plus a large number of accessory minerals, e.g. beryl, flourite, cassiterite, etc. Most pegmatites contain symmetrical zones that differ in mineral composition. |
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Term
Quartz Monzonite
(Adamellite) |
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Definition
| Coarse-grained plutonic rocks in which plagioclase and alkali feldspar are present in sub-equal amounts (each between 35 and 65% of total feldspar), quartz >20%, mafic minerals mainly biotite and hornblende. |
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Term
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Definition
| Coarse-grained plutonic rock containing >20% quartz, alkali feldspar is 10-35% of total feldspar, mafics 10-30% (biotite, hornblende) |
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Term
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Definition
| Medium to coarse-grained plutonic rocks. Quartz >20%, alkali feldspar <10% of total feldspar, mafics 20-40% (hornblende, biotite). |
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Term
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Definition
| Felsic variety of tonalite consisting principally of plagioclase and quartz with alkali feldspar and biotite as minor constituents. |
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Term
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Definition
| Quartz-mica rocks formed by the alteration of granites by pneumatolic fluids. Feldspars of original granite replaced by muscovite or Li-mica. Topaz usually present. |
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