SAC 101 Lecture 3 PPT.ppt
- 1. SAC 101 FUNDAMENTALS OF SOIL SCIENCE (2+1) LECTURE 3 SOIL GENESIS: SOIL FORMING ROCKS-DEFINITION, FORMATION, CLASSIFICATION OF ROCKS- IGNEOUS, SEDIMENTARY AND METAMORPHIC ROCKS
- 2. ROCKS A rock may be defined as a hard mass of mineral matter comprising two or more rock forming minerals – Eg. Granite and Gneiss Rocks are formed from the molten material known as magma. Magma is a mixture of molten or semi- molten rock, volatiles and solids that is found beneath the surface of the Earth.
- 3. Composition of earth crust – Over all ii.Sedimentary rocks - 5 % -Shales 4% -Sandstone 0.75% -Limestone 0.025% i.Igneous rocks - 95 %
- 4. Composition of upper 5 km of earth crust with rocks i.Sedimentary rocks- 74% -Shales 52% -Sandstone 15% -Lime stone- and dolomite 7% ii.Igneous rocks - 18 % -Granite 15% -Basalt 3% iii. Others - 8% Composition of earth crust – Over all ii.Sedimentary rocks - 5 % -Shales 4% -Sandstone 0.75% -Limestone 0.025% I. Igneous rocks - 95 %
- 5. Petrology The study of rocks is called Petrology (in Greek, petra means rock, logos means science) It consists of Petrography deals with the description of rocks - branch of science concerned with the composition and properties of rocks Petrogenesis is the study of the origin / formation of rocks
- 6. Formation of Rock- Various Processes Cooling and consolidation of Magma Within or on the surface of the earth Primary rocks or igneous rocks Disintegration & Decomposition and Transportation and cementation of fragmentary material Disintegrated either compacted insitu or transported by wind, water or ice to low lying areas Sedimentary rocks or secondary rocks Alteration of pre-existing rocks Primary & secondary rocks subjected to earth movement and to high temp and pressure or altered to new forms Metamorphic rocks
- 7. Rock Cycle
- 8. Classification of rocks Primary rocks or Igneous rocks Sedimentary or Secondary rocks Metamorphic rocks
- 9. a) Igneous or Primary rocks - Cooling and consolidation of molten material - magma within or on the surface of earth b) Sedimentary or Secondary rocks- Transportation and cementation of primary rocks a) Metamorphic rocks-Alteration of the existing primary and secondary rocks
- 10. a) Primary / Igneous rocks A.Extrusive or volcanic rocks consolidation of magma on the surface of the earth E.g. Basalt B.Intrusive or plutonic rocks Solidification of magma below the surface of the earth. Plutonic –greater depth Hypabassal -shallow depth Eg. Granite, syenite, diorite, Gabbro etc. Rocks formed in vertical cracks are called dykes Rocks formed in horizontal cracks are called sills. C.Vesicular rocks: Magma cools on the surface. Steam of water is entrapped into rocks and forms vesicles Eg.Pumice i.Based on mode of formation
- 11. Extrusive or volcanic rocks Intrusive or plutonic rocks
- 13. 2. Based on the Chemical Composition / Silica content 1. Acid rocks : >66% SiO2 (Granite, Rhyolite) 2. Intermediate : 56 to 66% SiO2 (Sub acid rocks 60 to 66% SiO2 (Syenite and Trachyte) (Sub basic rocks 56 to 60 % SiO2 (Diorite and Andesite) 3. Basic rocks: 40 to 55% (Gabbro, Basalt)
- 14. High Silica content forms light-colored rocks – Eg.Granite – Light coloured sandy soils with low Sp.gravity Entisols, Inceptisols Lower (but only by about 25%) Silica content forms darker-colored rocks – Eg.Basalt - dark coloured heavy soils with high Sp. Gravity – Black cotton soils- Vertisols
- 15. These Igneous rocks are found in bulks; do not have particles and layers; compact and massive; hard and resistant and have well- developed joints Non laminar massive structure
- 16. S.No Rocks Origin Essential minerals Common minerals Average specific gravity Remarks i. Granite Plutonic holocrystalline Quartz (20 to 30%) Hornblende, Magnetite, Mica 2.64 Light coloured white or reddish ii. Syenite Plutonic Holocrystalline Quartz, Orthoclase Hornblende, Magnetite, Biotite 2.80 Light coloured white or reddish iii. Diorite Plutonic Holocrystalline Quartz Hornblende, Magnetite, Biotite 2.85 Darker iv Gabbro Plutonic Holocrystalline Labradorite, Augite, Olivine Hornblende, Ilmenite 3.0 Blackish v. Dolerite Hypabasal Labradorite, Augite, Olivine Hornblende, Ilmenite 3.0 Blackish vi. Basalt Volcanic crystalline with glassy mass Labradorite, Augite, Olivine Hornblende, Ilmenite 3.0 Igneous rocks
- 17. II.Sedimentary Rock A sedimentary rock is a rock that is made of layers of sediments (sand, clay, mud) close to the earth’s surface. Sandstone
- 18. Sedimentary rocks Formed from the consolidation of sediments , derived from the breaking down of pre-existing rocks – transported through wind or water action at the surface of the earth. Deposited in layers or formed precipitates from aqueous solutions. Sediments with particles cemented together by substances like SiO2, Fe2O3 or lime CaCO3. Also called as clastic rocks. Stratification is the most common feature of these rocks and so these are also termed as stratified rocks.
- 19. A.Based on Mode origin 1.Residual 2.Transported Eg. Laterite a. Deposited as solids in suspension Eg Sandstone, Shale b. Deposited by chemical precipitation Eg Limestone, Ironstone c.Deposited through agency of organic matter Eg.Peat, Phosphatic deposits
- 20. B.Based on mode of formation 1.Fragmental, detrital or mechanically formed These are formed by the deposition and cementation of erosion products of pre-existing rocks – Shale, Conglomerate, Sandstone 2.Chemically formed i)Inorganically formed Formed by the evaporation or precipitation of material dissolved in sea or lake water- Halite, Gypsum Ca (HCO3)2 ---- CaCO3+ CO2 + H2O Limestone , Dolomite ii).Organically or biochemically formed Formed by the accumulation and partial decomposition of organic remains under anaerobic conditions e.g. peat, bituminous and semi bituminous coal.
- 21. C.Based on the grain size 1. Rocks with boulder, pebbles sized minerals (Rudaceous): Conglomerate 2. Rocks with sand size particles (Arenaceous) : Sandstone 3. Rocks with silt size particles (Silt rocks) :Siltstone 4. Rocks with clay size particles (Argillaceous) : Shale
- 22. Formation Weathering Transportation Deposition or Sedimentation Diagenesis
- 23. Formation 1. Weathering The igneous and other rocks disintegrate owing to physical, chemical and biological weathering. 2KAlSi3O8 + H2CO3+ H2O Al2Si2O5 (OH)4+K2CO3+ 4SiO2 Orthoclase Feldspar + Carbonic acid + Water Kaolinite + Potassium carbonate + Silica The products of these weathering provide the basic materials (gravels, sand, silt, mud) for the formation of sedimentary rocks.
- 24. 2. Transportation The disintegrated material is transported by the agencies such as water, wind, glaciers, runoff, and gravity. Dust of finer fractions carried by Wind-Saltation Deposition of colluvium (material which accumulates at the foot of a steep slope) at foot hillls- gravity - Solifluxion or Soil creep
- 25. 3. Deposition or Sedimentation The detrital materials, comprising minerals and rock fragments are deposited when the carrying agent has no longer energy enough to move further. Then Coarser particles settle first Finer particles settle later Deposition is called Graded Bedding
- 26. 4.Diagenesis Transformation of unconsolidated sediments into hard rock Compaction: compression of layers- water squeezed out. Clays, Shales Cementation: lime, silica, iron oxide Water that percolates carries the binding materials get deposited in voids of loose sediments and that on desiccation, binds to form rocks
- 27. Conglomerate –from cemented gravel Sandstone from sand Limestone Shale –from clay
- 28. c) Metamorphic rocks The primary and the secondary rocks when subjected to earth’s movement and to high temperature and pressure are altered to new rocks called Metamorphic rocks These are formed from igneous and sedimentary rocks under the influence of heat, pressure, chemically active liquids and gases. Change may occur in mineral composition or texture or both. The changes due to water is called hydro metamorphosim and due to pressure is called dynamo metamorphosim
- 29. Metamorphic rocks Formation The structure and mineral composition of metamorphic rocks depend on the composition of the original rock and the kind of metamorphism The banded or the laminated character is the most peculiar feature of metamorphic rocks Hydro metamorphism Dynamo metamorphism In thermal metamorphism, heat is the dominant factor which bring changes- also known as contact or additive metamorphism because there is an addition of magmatic material to the metamorphosed rock. In the case of dynamo-thermal metamorphism, the combination of pressure and heat forms one of the most powerful metamorphic forces leading to more or less complete recrystallization of minerals with new structures
- 30. Based on the texture and structure, MR divided into three groups 1.Foliated – Gneiss, Schist, Slate 2.Non foliated - Anthracite 3.Granular – Marble, Quartzite Foliation in geology refers to repetitive layering in metamorphic rocks Each layer can be as thin as a sheet of paper, or over a meter in thickness. The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure
- 31. Gneiss - a foliated metamorphic rock
- 32. Metamorphic Rocks Sand stone (SR) : Quartzite Shale (SR) : Slate, Schist Lime stone / Dolomite : Marble (SR) Granite (IR) : Granite Gneiss Dolerite (IR) : Hornblende Gneiss
- 33. Quartz (Mineral) and Quartzite
- 35. how heat and pressure changes these rocks … Sedimentary Metamorphic Shale Slate
- 36. Check out how heat and pressure changes these rocks … Igneous Metamorphic Granite Gneiss
- 37. Gneiss Bands