Term
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Definition
Plagioclase felspar >2/3 total feldspar
Calcic plagioclase An50-100
Potash felspar <10% total feldspar
Quartz <10%; Feldspathoids <10%
Chiefly pyroxene, olivine
Saturated and Unsaturated
CI usually >40
Volcanic: Gabbro, Norite, Troctolite, Anorthosite, Alkaline Gabbro, Diabase
Plutonic: Tholeiitic Basalts and Diabases, Alkali Olivine Basalts, Hawaiite, Mugearite |
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Term
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Definition
Little or no Feldspar (Plagioclase 0-10%)
Chiefly Pyroxene and/or Olivine
Chiefly Serpentine, Iron Oxides, Hornblende, Biotite
Undersaturated
CI 90-100
Plutonic: Peridotite, Pyroxenite, Hornblendite |
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Term
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Definition
| Volcanic, holocrystalline-hypocrystalline, rarely vitreous, with aphanitic groundmass; plagioclase (labradorite) 40-60%; mafics (clinopyroxene, olivine) 55-35% |
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Term
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Definition
| Plagioclase and pyroxene principal constituents; Mg olivine present as phenocrysts; groundmass pyroxenes commonly pigeonite, or subcalcic augite, more rarely hypersthene. Interstitial siliceous glass or quartz may be present. Oceanic varities have >2.5% TiO2; continental varieties =1% TiO2 |
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Term
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Definition
| Plagioclase and pyroxene principal constituents. Pyroxenes are augite and hypersthene or pigeonite. Considerable olivine may be present, which may have reaction rims of pyroxene. Oceanic varieties have >2.5% TiO2; continental =1% TiO2 |
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Term
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Definition
| Plagioclase and pyroxene principal constituents. Pyroxene is augite, rarely pigeonite or hypersthene. Typically non-porphyritic; olivine common, with or without reaction rim of pyroxene. Al2O3 17%, TiO2 = 1%; intermediate characterristics between tholeiites and alkali types |
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Term
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Definition
| Abundance of Mg olivine, commonly in two generations, phenocrysts and groundmass; one pyroxene - titanaugite (slight purple pleochroism). Feldspathoids, alkali feldspar, phlogopite or kaersutite may be present; no reaction rims of pyroxene on olivine. Total alkali content higher and silica lower than types above. |
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Term
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Definition
| Basaltic rocks rich in olivine phenocrysts. |
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Term
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Definition
| Basaltic rich in both augite and olivine phenocrysts. |
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Term
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Definition
| Basic rock containing plagioclase of highly sodic composition (albite); produced by metasomatic alteration of basalts; mafic minerals generally partly or completely altered to serpentine, chlorite, epidote. |
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Term
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Definition
| Fine-grained non-porphyritic or sparsely porphyritic rock; when present, phenocrysts include labradorite, titanaugite, and olivine; groundmass dominated by lathes of andesine with interspersed granules of augite, olivine and magnetite. |
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Term
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Definition
| Plagioclase most abundant constituent (65 - 70%), and dominates texture by sub-parallel alignment. Microphenocrysts of plagioclase (when present), and larger groundmass plagioclase have cores of albite-twinned sodic andesine with clear rims of Ca-anothoclase; numerous microphencrysts of olivine; Ca-pyroxene is usually inconspicuous; magnetite plentiful. |
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Term
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Definition
| Intrusive, holocrystalline varying from coarse to medium grained; plagioclase plus augite; olivine or hornblende prominent in correspondingly designated varities. |
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Term
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Definition
| Intrusive, normally holocrystalline usually containing mafics (various pyroxenes, less common olivine) 65-25%. plagioclase 30-70%. Fine- to medium-grained and even-grained, often ophitic. Occurs as shallow intrusives such as sills, dikes, laccoliths and plugs. |
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Term
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Definition
| Intrusive, holocrystalline, plagioclase plus hypersthene, typically with subordinate augite; olivine present in some rocks. |
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Term
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Definition
| Intrusive, holocrystalline, predominatly plagioclase plus olivine. |
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Term
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Definition
| Intrusive, holocrystalline, plagioclase the dominant or only mineral, minor hypersthene or augite common. |
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Term
| Peridotite (Varies based on type of mafic mineral) |
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Definition
| Holocrystalline, contains mafics (olivine, pyroxene, hornblende) 85-95%; ores (magnetite, ilmenite, chromite) 10-30%; calcic plagioclase <5%. |
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Term
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Definition
Mafic Mineral Rock
Olivine Dunite
Olivine + Orthopyroxene Harzburgite
Olivine + Clinopyroxene (Augite) Weherlite
Olivine + Orthopyroxene + Clinopyroxene Lherzolite
Orthopyroxene + Clinopyroxene Websterite
Pyroxene (Orthopyroxene, augite +/- Olivine +/- Hornblende)Pyroxenite
Hornblende +/- Olivine +/- Pyroxene Hornblendite
Garnet + Enstatite + Diopside Garnet Peridotite
Olivine + Pyroxene + Plagioclase (subordinate) Plagioclase-Peridotite |
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Term
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Definition
| Holocrystalline, Mg olivine, phlogopite, Cr-diopside, enstatite, Mg garnet, and ilmenite in groundmass of serpentinized olivine and calcite. |
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Term
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Definition
| Volcanic rock of peridotitic or closely related composition; devitrified glass a characteristic constituent; spinifex texture (produced by rapid quenching from high temperature); two varities: peridotitic komatiites - rich in olivine phenocrysts and chrome spinel, in a groundmass of finely crystallized pyroxene; Pyroxenitic komatiites - olivine less abundant and subcalcic augite more plentiful; neither rock contains plagioclase; essentially restricted to the Pre-Cambrian. |
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