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Rocks.ppt
- 1. 1 SOIL FORMING ROCKS Lecture # 03 7-Feb-23 © ARR
- 2. 2 ROCKS • What are rocks? • How are rocks formed? • How are rocks classified? 7-Feb-23 © ARR
- 3. 3 Rocks Defined • A rock may be defined as “an aggregate of one or more minerals” [An aggregate of single mineral calcite gives rise to crystalline limestone Granite is a combination of several minerals] 7-Feb-23 © ARR
- 4. 4 Classification of Rocks By origin, 3 great divisions of rocks are recognized: • Igneous rocks • Sedimentary rocks • Metamorphic rocks 7-Feb-23 © ARR
- 5. 5 Igneous Rocks • Igneous (Latin) means “made from fire or heat” • When volcanoes erupt and liquid rock comes up to earth's surface, new igneous rock is made • When the rock is liquid & inside the earth, it is called “magma” • Magma comes from the Earth’s core which is molten rock • Igneous rocks form when molten magma cools and turns into solid rock 7-Feb-23 © ARR
- 6. 6 Classification of Igneous Rocks Based on mode of origin 1. Intrusive or Plutonic [Granite, Diorite, Gabbro, Peridotite] 2. Extrusive or Volcanic [Basalt, Rhyolite, Andesite] Intrusive rocks named after Pluto, the Roman God of the underworld. Volcanic rocks named after Vulcan, the Roman God of fire. 7-Feb-23 © ARR
- 8. 8 Classification of Igneous Rocks Based on chemical composition 1. Acidic (65-75% SiO2) [Granite,Rhyolite] 2. Neutral (55-65% SiO2) [Andesite] 3. Basic (45-55% SiO2) [Basalt, Diorite] 4. Ultra basic (40-45% SiO2) [Picrite, Gabbro, Limestone] 7-Feb-23 © ARR
- 9. 7-Feb-23 © ARR 9 GRANITE
- 12. 12 Sedimentary Rocks • Sedimentary rocks cover 75% of the earth’s surface • Most of the rocks found on the Earth’s surface is sedimentary even though sedimentary rocks only make up less than 5% of all the rocks that make up Earth 7-Feb-23 © ARR
- 13. 13 Sedimentary Rocks • When rocks are exposed to the elements – air, rain, sun, freeze / thaw cycle, plants – erosion occurs and the little bits of rock worn away get deposited as sediments • Over time, these sediments harden as they get buried by more sediments and turn into sedimentary rocks • Sedimentary rocks are usually formed in layers (strata) 7-Feb-23 © ARR
- 14. 14 Sedimentary Rocks 7-Feb-23 © ARR
- 15. 15 Kinds of Sedimentary Rocks Based on appearance Sedimentary Rock Composition Conglomerate Pebbles, boulders cemented in a matrix Sandstone Sand grains cemented Shale Clay hardened into a rock Limestone Made of calcium carbonate Gypsum, etc. When seawater evaporates Porphory Jagged rock bits cemented 7-Feb-23 © ARR
- 16. Kinds of Sedimentary Rocks Based on origin Type Description Example Residual Formed in situ Laterite Transported Deposited as solids in suspension Sandstone, Shale Deposited by chemical precipitation Limestone Iron stone Deposited through agency of organic matter Peat Phosphatic deposits 16 7-Feb-23 © ARR
- 17. Kinds of Sedimentary Rocks Based on grain size • Rudaceous: Rocks consisting chiefly of boulders [Conglomerate] • Arenaceous: Rocks consisting chiefly of sand grade materials [Sandstone] • Silt rocks: Rocks consisting chiefly of silt- sized particles [Silt stone] • Argillaceous: Rocks consisting chiefly of clay sized particles [Shale] 17 7-Feb-23 © ARR
- 21. 21 Metamorphic Rocks • Rocks that have changed • Greek "meta" and "morph” “to change form” • Originally these were igneous or sedimentary • Metamorphism brought about by water, heat, pressure or chemically active liquids and gases • Changes brought about are both physical and chemical • Hydro-, thermo-, dynamo-metamorphism 7-Feb-23 © ARR
- 22. 22 Metamorphic Rocks • The least common of the 3 kinds of rocks • Igneous or sedimentary rocks transformed by great heat or pressure • Slate is transformed shale, splits into smooth slabs • Schist, the most common metamorphic rock • Marble is transformed limestone • Quartzite is very hard 7-Feb-23 © ARR
- 23. Metamorphic Rock Sedimentary Rock Metamorphic Form Sandstone Quartzite Limestone Marble Shale Slate Clay Schist Granite Granite gneiss 7-Feb-23 © ARR 23
- 26. 7-Feb-23 © ARR 26 SLATE
- 28. 28 Key References Daji: A Text Book of Soil Science Any book on Geology www.geology.com 7-Feb-23 © ARR