Soil Genesis: Soil Forming Rocks - Lecture Notes

Soil genesis: Soil forming rocks- Definition, Formation, Classifi cation of rocks-Igneous, Sedimentary and Metamorphic rocks 1 Rock s ⚫ The rocks which form the earth are made up of minerals ⚫ Defined as a hard mass of mineral matter...

Soil genesis: Soil forming rocks- Definition, Formation, Classifi cation of rocks-Igneous, Sedimentary and Metamorphic rocks 1 Rock s ⚫ The rocks which form the earth are made up of minerals ⚫ Defined as a hard mass of mineral matter comprising two or more rock forming minerals (eg) Granite and Gneiss ⚫ Physical and chemical composition vary with the characteristics of the minerals ⚫ Formed from the molten material known as magma. Magma is a mixture of molten or semi- molten rock, volatiles and solidifies that is found beneath the surface of the Earth. 2 Roc ks ⚫ Petrology is the study of rocks (in Greek, petra means rock, logos means science ⚫ 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 ⚫ Monomineralic minerals are rocks that are composed of only one mineral. Eg. Dunite 3 Occurrence of rocks Sediment Shales (52%) 74% ary Sandstone (15%) rocks Limestone dolomite (7%) Igneous Granite (15%) 18 % rocks Basalt (3%) Others 8% 4 Formation – 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 5 Types of rocks 1. Based on the mode of formation ⚫ Primary rocks or Igneous rocks ⚫ Sedimentary or Secondary rocks ⚫ Metamorphic rocks 6 Igneous rocks ⚫ Solidification of moltenmagma, N on laminar massive structure 7 Sedimentary rocks ⚫ These rocks are 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 ⚫ These rocks are also called as clastic rocks. ⚫ Also known as stratified rocks 8 Sedimentary rocks ⚫ Formed through four stages 1. Weathering 2. Transportation 3. Deposition 4. Diagenesis (Transformation of unconsolidated sediments into hard rocks) 9 Metamorphic rocks ⚫ Undergone somechemical or physical change from its original form ⚫ They are formed the transformation of from subsequent igneous rocks and sedimentary ⚫ There are two broad classes of metamorphism ⚫ Thermal: Dominant factor heat ⚫ Dynamothermal: C ombined effect of pressure and heat 1 0 Metamorphic rocks Rocks Metamorphic rock Sandstone : Quartzite Shale : Slate/ Schist Limestone : Marble Granite : Granite gneiss Dolerite : Hornblende 1 1 Thank you…… 1 2