Term
| Alkali Intermediate Rocks 1 |
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Definition
Alkali Feldspar >2/3 total Feldspar
Quartz < 10%
Feldspathoid <10%
CI 15
Cheifly hornblende, biotite, pyroxene, muscovite
Plutonic: Syenite
Volcanic: Trachyte |
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Term
| Alkali Intermediate Rocks 2 |
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Definition
Alkali Feldspar 1/3-2/3 total Feldspar
Quartz <10%
Feldspathoid <10%
CI 25
Chiefly hornblende, biotite, pyroxene
Plutonic: Monzonite
Volcanic: Latite |
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Term
| Plagioclase Intermediate Rocks |
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Definition
Plagioclase (An20-50) >2/3 total Feldspar
Quartz <10%
Feldspathoid <10%
CI 25
Chiefly hornblende, biotite, pyroxene
Plutonic: Diorite
Volcanic: Andesite |
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Term
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Definition
| Volcanic holocrystalline or hypocrystalline with (usually porphyritic) aphanitic groundmass; plagioclase is the greatly predominate or only feldspar (55-70%); mafics 40-25% (hornblende, pyroxenes (ortho and clino), and biotite). Olivine may be present in more basic varities. |
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Term
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Definition
| Volcanic, usually porphyritic with holocrystalline to vitreous aphanitic matrix; sodic plagioclase (50-30%), potash feldspar (45-20%); mafics 15-60%, average 30% (biotite, hornblende, augite); potash feldspar usually confined to groundmass or as rims around plagioclase. |
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Term
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Definition
| A type of latite containing large phenocrysts of plagioclase (An20-40) that make up 30-45%. Alkali feldspar is the principal or sole feldspar of the groundmass. Color Index of 10-20. Usual mafic component is clinopyroxene (typically aegrine-augite), with minor chlorite, calcite, oxides and apatite. |
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Term
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Definition
| Volcanic, holocrystalline to hypocrystalline, usually porphyritic, rarely vitreous, with aphanitic groundmass; potash felspar (45-80%); sodic plagioclase (25-5%); mafics - biotite, amphibole, pyroxenes (30-10%); peralkaline trachytes contain sodic amphiboles and/or pyroxenes, and a sodic alkali feldspar. |
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Term
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Definition
| Metasomatized intermediate rocks with phenocrysts of sodic plagioclase, hornblende or diopside set in a felted or trachtic groundmass composed of albite or oligoclase, chlorite, epidote, magnetite, sphene and apatite. |
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Term
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Definition
| Altered andesitic rocks produced by hydrous deuteric fluids. Appear green in hand specimen. Characterized by hornblende replaced by chlorite and calcite; pyroxenes replaced by bastitic serpentine, chlorite and calcite; plagioclase becomes albitized together with concomitant crystallization of epidote. |
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Term
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Definition
| Volcanic rock intermediate between basalt and andesite; typically contains phenocrysts of olivine, hypersthene, augite and plagioclase set in a glassy groundmass containing plagioclase laths and granules of pyroxene. |
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Term
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Definition
| Intrusive, holocrystalline, phaneritic rocks containing sodic plagioclase (andesine or oligoclase) - 50-30%; potash feldspar (orthoclase) - 45-20%; mafics (biotite, hornblende, augite) - 40-25%. |
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Term
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Definition
| Intrusive, holocrystalline, phaneritic with potash feldspar - 30-80%; sodic plagioclase - 5-25% (may be absent or accessory); mafics (biotite, amphibole, pyroxene). |
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Term
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Definition
Orthoclase, microperthitic orthoclase, rarley microcline
Oligoclase, less commonly andesine
Biotite
Green hornblende
Diopside augite
Accessory quartz |
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Term
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Definition
Microperthitic orthoclase, anorthoclase
Albite, sodic oligoclase
Iron-rich biotite
Arfvedsonite, hastingsite, barkevikite
Titanaugite, aegerine-augite
Accessory feldspathoids |
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Term
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Definition
| Medium to coarse-grained rocks in which andesine or calcic oligoclase is the predominant mineral, and hornblende and biotite are the chief mafic constituents. Textures are variable, most have granitic textures, but poikilitic and porphyritic textures and characteristics of many. Often segregation of light and dark minerals into irregular clots. Quartz and orthoclase may be present in small amounts. |
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