Classifications of igneous rocks
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Igneous rock forms through the cooling and solidification of magma or lava. It is classified based on several properties including genesis, texture, color, and chemical composition. Based on genesis, igneous rocks are classified as plutonic (cooled at depth), hypabyssal (cooled at shallow depth), or volcanic (cooled on the surface). Texture classifications include phaneritic, aphenitic, porphyritic, and poikilitic. Color classifications are based on the percentage of mafic minerals and include leucocratic, mesocratic, melanocratic, and hypermelanic. Chemical composition classifications include peraluminous, metaaluminous, subaluminous, and several
Classifications of igneous rocks
- 2. Igneous rock (derived from the Latin word ignis meaning fire) is one of the three main rock types, the others being sedimentaryand metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface asintrusive (plutonic) rocks or on the surface as extrusive(volcanic) rocks. There are several Classification based on different properties.
- 3. GENETIC CLASSIFICATION BASED ON COLOR TEXTURAL CHEMICAL COMPOSITIONAL CIPW CLASSIFICATION IUGS CLASSIFICATION
- 4. Based on genesis of igneous rock it is mainly classified in to 3 I. Hypabyssal rocks – find at shallow depth (<1km) ,fine grained II. Plutonic igneous rock- depth greater than1 km, medium to coarce grained III. Volcanic rocks- magma which reaches & flow on the surface, is called lava and forms extrusive rocks, they are fine grained
- 5. Here it is classified based on the volume percentage of colored mineral or mafic mineral. Leucocratic-contain lessthan 30% mafic mineral Mesocratic- contain 30%-50%mafic mineral. Melanocratic- contain 60-90% mafic mineral. Hyper melanic-contain more than 90% mafic mineral
- 6. This is based on the relationship of th individual grains in arock 1- Phaneritic texture- in this texture we can identify the individual grains with our naked eye. It showing in intrusive rock body, by slow cooling . 2-Aphenitic texture- individual grains can’t idenitfy with naked eye. Its very fine grained texture seen in fast cooling extrusive rocks. 3-Porphyritic texture- large crystals (phenocryst) are embedded in smaller ground mass. 4-Poikilitic texture- smaller grains(chadacryst) are accommodated in larger grains(oikocryst)
- 7. Peraluminous rocks- the total content Na2O+CaO+K2O<that of alumina. Metaaluminous rock- the content of Na2O+K2O<Al2O3 but the total content of Na2O+K2O+CaO>Al2O3. Subaluminous- Al2O3= K2O+Na2O. Peralkaline- K20+Na2O>Al2O3. Peralkalic –Al2O3<Na2O+K20.
- 8. - Cross ,Iddings,Pirson and Washington. - Two types:-1) Normative (Norm) - 2) Model minerals (Mode) Normative minerals:-Assumed or assemption minerals which are normally present in the rock. Model minerals:- Actual minerals present in the rock,expresed has volume percentage .
- 9. Based on genesis of Igneous rocks it mainly classified in to 3, the are plutonic, hypabysal, &plutonic. Based on texture also it is classified as phaneritic, aphenitic, porphyritic & poikilitic. Based on color index also it is classified as leucocratic ,mesocrstic , melanocratic &hyper melanic. Based on chemical content also it is classified
- 10. Igneous and metamorphic petrology(1962), Francis J.Turner,McGraw-Hill book company. http://en.wikipedia.org/wiki/Granite http://www.thefreedictionary.com/granite