SAC 101 Lecture 4 PPT.ppt.pdf about soil
- 1. Lecture No.4 Brief description of important rocks-Mineralogical composition
- 2. Igneous Rocks ❖Igneous rocks are defined as types of rocks that are formed when molten rock (rock liquefied by intense heat and pressure) cools to a solid-state. ❖Lava is molten rock flowing out of fissures or vents at volcanic centers. ❖Pyroclastic deposits are accumulations of fragmented material ejected during volcanic eruptions. ❖Igneous rocks can be easily identified with their texture, density, color, and mineral composition. ❖Its texture depends on the shape, size, time period to cool down and solidify, and the arrangement of crystals in the rock.
- 3. ❖ Igneous Rocks are formed by crystallization from a liquid, or magma. ❖ Magmas are less dense than surrounding rocks, and will therefore move upward. ❖ If magma makes it to the surface it will erupt and later crystallize to form an extrusive or volcanic rock. ❖ If it crystallizes before it reaches the surface it will form an igneous rock at depth called a plutonic or intrusive igneous rock.
- 5. Sedimentary rocks Formed by/from • Agency of water- Called as aqueous rocks. • Sediments brought by water. • Sediment contain various types of substances and sizes of particles. • Particles are cemented by silica, iron oxide or lime to a consolidated form. • Rocks deposited in layers or strata –called as stratified rocks. • formed by cooling, evaporation or by direct chemical precipitation. • Secondary of origin
- 7. Sedimentary rocks-Six groups • Arenaceous • Argillaceous rocks • Calcareous rocks • Carbonaceous rocks • Siliceous rocks • Precipitated salts
- 8. Arenaceous: • Formed of the deposits of coarse grained particles. • Composed of siliceous material derived from disintegration of older rocks. • Fragmental material s deposited in beds of varying thickness by water. • E.g. Sandstone, grit, conglomerate and breccia.
- 10. Argillaceous rocks • Composed of hydrated silica of alumina in admixture with sand, other silicates & calcareous matter. • Clay deposited mainly of silicate of alumina - kaolin or China clay. • E.g. clay, Mudstone, Shale and Fuller’s earth.
- 11. MUD STONE Shale
- 12. Calcareous rocks • Consists of carbonate of lime or lime and magnesia. • May be of sedimentary origin or formed by chemical precipitation or by organic agency (debris from plant and animal life). • Found in layers • Layers vary in depth of thickness.
- 13. • Formed by chemical precipitation, the calcareous material is deposited in the form of layers/sheets from waters containing calcium carbonate in solution. • The precipitate when first formed is usually soft and chalky, but soon acquires a hard, compact structure and crystalline texture. • E.g: limestone, chalk, magnesia, ferruginous lime stones, dolomite, marls of various varieties and coral.
- 14. Carbonaceous rocks • Formed from decomposing vegetation under anaerobic conditions. • When plants undergo decomposition under restricted air supply, greater portion of the carbonaceous matter is retained and the material is slowly converted into coal. • E.g. peat, lignite, coal, anthracite.
- 15. Siliceous rocks • Siliceous rocks of organic origin formed from parts of minute plants and animals like diatoms, radiolaria etc., • Some are soft and friable and crumble to powder very easily. • Others like flint and chert are hard and compact.
- 16. Precipitated salts • Consist mainly of deposits formed as rock masses either by cooling, evaporation or by chemical precipitation. • Water charged with acid or alkaline material, acting under pressure under subterranean regions, dissolves various mineral substances from rocks. • The salts thus formed deposit as rocks and such rocks vary in composition.
- 17. Oxides : e.g. hematite, limonite, bauxite and quartz. Carbonates: e.g. stalactite, stalagmite, magnetite and limestone. Sulphates: e.g. gypsum Phosphates: e.g. phosphorite Chlorides: e.g. rock salt.
- 18. Metamorphic rocks • The igneous and sedimentary rocks after they were first formed sometimes undergo a change. • When the change is considerable, the rock is said to have undergone metamorphosis and the new rock is known as a metamorphic rock. • The metamorphism brought about by the action of water, heat or pressure or by the combined action of any one of these or all.
- 19. • Change brought by water is hydro-metamorphism. heat is thermo-metamorphism. pressure is dynamo- metamorphism.
- 20. Examples • By the introduction of a cementing material like silica, lime or iron oxide, loose sand may be turned into a sandstone or a sandstone into a quartzite. • By the removal of certain constituents by percolating waters, basalt or granite may be converted into a laterite.
- 21. • Due to pressure, the crystals of the original rock get pressed or flattened & new rock is foliated. • When foliation is slight, the layers are inseparable it is called as gneiss. • If foliation is complete with distinct & separable layers it is called as schist.
- 22. Mineralogical composition of important rocks S. Rocks Grain size Essential minerals Most common accessory minerals Avg. sp. Gr. Remarks (i) Igneous rocks 1. Granite Plutonic Holocryst alline Predominant quartz 20-35 orthoclase Hornblende mica, magnetite 2.64 Light coloured, White or reddish 2. Syenite - do - Predominance quartz 100% plus of orthoclase, nepheline and albite Hornblende , biotite, magnetite 2.08 - do - 3. Granodiorite - do - Intermediate quartz plagioclase exceeds orthoclase - do - 2.07 Medium coloured reddish
- 23. 4. Diorite - do - Intermediate quartz absent plagioclase - do - 2.85 Darker 5. Gabbro - do - Labradorite augite + olivine Hornblende, ilmenite 3.00 Blackish 6. Dolerite Hypabyssal ophitic texture - do - - do - 3.00 -do – 7. Basalt Volcanic micro crystalline with glassy mass - do - - do - 3.00 - do -
- 24. S. N o Name of the type Mineral composition Colour and structure (ii) Sedimentary rocks 1. Sandstone Mainly quartz with same contents, such as calcium carbonate, iron oxides and clays Light to red, usually granular in structure 2. Shale Clay minerals, quartz and some organic matter Light to dark thinly laminated structure 3. Limestone Mainly calcite or calcite and dolomite with some iron oxides, clay, phosphate and organic matter Usually light grey to yellow usually fine grained and compact
- 25. iii Metamorphic rocks 1. Gneiss Formed from granite, mineral composition like that of granite Alternating light and dark colours. Banded and foliated structure 2. Schist Formed from basalt or shales. Mineral composition much as that of original rock Much as original rock, foliated structure 3. Quartzite Formed from sandstone and of same composition Light to brown. Compact and uniform texture, foliated structure 4. Slate Formed from shale and of same composition Grey to black, compact, and uniform texture foliated structure 5. Marble Formed from limestone Light red, green, black, compact, fine to coarse texture, non-foliated structure SI. No Type Mineral composition Colour and structure