Textural classification of igneous rocksSlide 2Compositional terms for igneous rocksClassification of common igneous rocksPowerPoint PresentationClassification of Igneous RocksClassification of Phaneritic Igneous RocksSlide 8Classification of Aphanitic Igneous RocksSlide 10Slide 11Igneous TexturesSlide 13Slide 14Slide 15Slide 16Slide 17Michel-Levy method for determining feldspar compositionTextural classification of Textural classification of igneous rocksigneous rocksPhaneritic: Phaneritic: crystals visible with naked eyecrystals visible with naked eyePlutonic Plutonic oror intrusive rocks intrusive rocksAphanitic: Aphanitic: crystal too small for naked eyecrystal too small for naked eyeVolcanic Volcanic oror extrusive rocks extrusive rocksPorphyritic:Porphyritic: two different, dominant grain sizestwo different, dominant grain sizesLarge xtals = Large xtals = phenocrystsphenocrysts; small xtals = ; small xtals = groundmassgroundmassFragmental: Fragmental: composed of disagregated igneous materialcomposed of disagregated igneous materialPyroclastic rocksPyroclastic rocksTextural classification of Textural classification of igneous rocksigneous rocksPegmatitic: Pegmatitic: very large xtals (cm to 10s of cm); i.e., very large xtals (cm to 10s of cm); i.e., slowlyslowly cooled cooledForms veins or layers within plutonic bodyForms veins or layers within plutonic bodyGlassy: Glassy: non-crystalline; cools very fast (e.g., obsidian)non-crystalline; cools very fast (e.g., obsidian)Volcanic rocksVolcanic rocksVesicular:Vesicular: vesicles (holes, pores, cavities) form as gases expandvesicles (holes, pores, cavities) form as gases expand Volcanic rocksVolcanic rocksCompositional terms for Compositional terms for igneous rocksigneous rocksFelsic: Felsic: felfeldspar + dspar + sisilica lica ~55-70% silica, K-feldspar > 1/3 of feldspars present~55-70% silica, K-feldspar > 1/3 of feldspars present light-colored silicate minerals — Continental crustlight-colored silicate minerals — Continental crustIntermediate:Intermediate: between felsic and mafic between felsic and mafic ~55-65% silica, plag > 2/3 of feldspars present~55-65% silica, plag > 2/3 of feldspars present Na-rich plag predominates over Ca-rich plagNa-rich plag predominates over Ca-rich plagMafic: Mafic: mamagnesium + gnesium + feferric ironrric iron ~45-50% silica; Ca-rich plag dominant feldspar~45-50% silica; Ca-rich plag dominant feldspar dark silicate minerals — Oceanic crustdark silicate minerals — Oceanic crustUltramafic: Ultramafic: >90% mafic minerals, silica < 45%, few or no feldspars>90% mafic minerals, silica < 45%, few or no feldspars Mantle-derivedMantle-derivedClassification of common igneous rocksClassification of common igneous rocksCompositionCompositionPhaneriticPhaneriticAphaniticAphaniticColor indexColor index(% dark minerals)(% dark minerals)FelsicFelsicGraniteSyeniteMonzoniteRhyoliteTrachyteLatite101520IntermediateIntermediateGranodioriteDioriteDacite Andesite2025MaficMaficGabbro Basalt50UltramaficUltramaficPeridotite95Composition of Igneous RocksComposition of Igneous RocksClassification of Igneous RocksClassification of Igneous RocksFigure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.Classification of Classification of Phaneritic Phaneritic Igneous RocksIgneous RocksFigure 2-2. A classification of the phaneritic igneous rocks. a. Phaneritic rocks with more than 10% (quartz + feldspar + feldspathoids). After IUGS.The rock must contain a total ofat least 10% of the minerals below.Renormalize to 100% (a)Quartz-richGranitoid909060602020Alkali Fs.Quartz SyeniteQuartzSyeniteQuartzMonzoniteQuartzMonzodioriteSyeniteMonzoniteMonzodiorite(Foid)-bearingSyenite5103565(Foid)-bearingMonzonite(Foid)-bearingMonzodiorite90Alkali Fs.Syenite(Foid)-bearingAlkali Fs. Syenite10(Foid)Monzosyenite(Foid) Syenite(Foid)Monzodiorite(Foid) GabbroQtz. Diorite/Qtz. Gabbro510Diorite/Gabbro/Anorthosite(Foid)-bearingDiorite/Gabbro60(Foid)olitesQuartzoliteGraniteGrano-dioriteTonaliteAlkali Feldspar GraniteQAPF60Plutonic rocksClassification of Igneous RocksClassification of Igneous RocksFigure 2-2. A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS.PlagioclaseOlivinePyroxeneGabbroTroctoliteOlivine gabbroPlagioclase-bearing ultramafic rocks90(b)AnorthositeOlivineOlivineClinopyroxeneClinopyroxeneOrthopyroxeneOrthopyroxeneLherzoliteLherzoliteHarzburgiteWehrliteWebsteriteOrthopyroxeniteOrthopyroxeniteClinopyroxeniteClinopyroxeniteOlivine WebsteritePeridotitesPeridotitesPyroxenitesPyroxenites90401010DuniteDunite(c)GabbroicrocksUltramaficrocksClassification of Classification of AphaniticAphaniticIgneous RocksIgneous RocksFigure 2-3. A classification and nomenclature of volcanic rocks. After IUGS. (foid)-bearing Trachyte(foid)-bearing Latite(foid)-bearing Andesite/Basalt(Foid)ites10606035651020206060FAPQRhyolite DaciteTrachyte Latite Andesite/BasaltPhonoliteTephriteVolcanic rocksClassification of Igneous RocksClassification of Igneous RocksFigure 2-4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University Press.Classification of Igneous RocksClassification of Igneous RocksFigure 2-5. Classification of the pyroclastic rocks. a. Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. b. Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1, 287-298. Pyroclastic rocksIgneous TexturesIgneous TexturesFigure 3-5. a. Figure 3-5. a. Compositionally Compositionally zonedzoned hornblende phenocryst with hornblende phenocryst with pronounced color variation visible pronounced color variation visible in plane-polarized light. Field in plane-polarized light. Field width 1 mm. width 1 mm. b.b. Zoned plagioclase Zoned plagioclase twinned on the carlsbad law. twinned on the carlsbad law. Andesite, Crater Lake, OR. Field Andesite, Crater Lake, OR. Field width 0.3 mm.width 0.3 mm. © John Winter and © John Winter and Prentice Hall.Prentice Hall.Figure 3-6.Figure 3-6. Examples of plagioclase zoning profiles determined by microprobe point traverses. Examples of plagioclase zoning profiles determined by microprobe point traverses. a. a. Repeated Repeated sharp reversals