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Primary silicate minerals

Important Primary minerals

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Important Primary minerals

=>Quartz – SiO2.

=>Potash feldspar (Orthoclase) – KAlSi3O8, Soda feldspars (Albite) – NaAlSi3O8

=>Lime feldspar (Anorthite) – CaAl2Si2O8; Albite and anorthite combine to form plagioclase or soda lime feldspars.

=>Feldspars are easily attacked by “water containing H2CO3”. The weathering process is called as carbonation.

=>Plagioclase weathers more rapidly than orthoclase.

=>Orthoclas is commonly occurring feldspar mineral in acid igneous rocks.

=>Micas are the double silicates of K and Al with or without iron. These are plate like structures.

1. Muscovite (white mica) – KAl3Si3O10(OH)2
2. Biotite (black mica) – occurs both in acidic and basic rocks.
3. Phlogopite – Occurs as a primary mineral in igneous rocks.

=>Biotite is easily weatherable than muscovite.

=>Pyroxenes and amphiboles: These are the double silicates of Fe, Mg, Al and Ca.

=>Pyroxene – Augite (dark green)

=>Amphibole – Hornblende (green – black)

=>Olivines are the “thin silicates of Fe and Mg”. Eg: Fayalite, forsterite.

=>Sedimentary rocks have more of secondary minerals.

=>Muscovite alters to “hydrous mica”.

=>The insoluble residual material left behind during weathering is called as “saprolite”.

=>The phenomenon of weathering of surface layer of rocks due to differential co-efficient of
expansion and contraction leading to ultimate disintegration is called “exfoliation”.

=>The material deposited due to melting of ice or glacier in warm regions forms a structureless mass and is termed “moraine or till”.

=>Chemical weathering of feldspar produces clay mineral.

=>Basalt decomposes more easily than granite.

=>Ease of weathering of minerals

=>Quartz > Feldspar > Micas > Olivines > Hornblende.

=>Weathering is a denstructive process whereas soil formation is a constructive porcess in nature.

=>Relief: It is defined as the elevations and inequalities of a land surface considered collectively. “Topograpy” is similar to relief to be used on contour maps.

=>The time devoted by nature to the formation of soil is known as “pedogenic time”.

=>The process leading to the development of “soil profile” is called “pedogenic process”.

=>“Humification” is the process of decomposition of raw O.M into humus. This process usually takes place in surface or O horizon.

=>‘Eluviation” is the process of removal of constituents by percolation from upper layer to lower layer (wash out).

=>“Illuviation” is the deposition of dissolved material in the lower layers (wash in).

=>“Podzole” means ash like under. Podzolisation is humid temperate type of soil forming process. It is opposite to “calcification”.

=>Laterization is the process of soil formation in tropics and sub-tropics. Laterization is the process of removal of “silica” instead of “sesquioxides” from the upper layers.

=>Laterization and podzolisation form soils belonging to the group of “pedalfer”.

=>“Calcification” occurs in areas where there is insufficient rainfall.

=>The soils which are having high saturation of ‘Ca’ are called as “pedocals”.

=>“Decalcification” is the removal of ‘Ca’ ions (or) CaCO3 by leaching.

=>“Cation exchange capacity” is expressed as me/100 g of soil or cmol (p) kg-1 soil.

=>Soil cations are sometimes called as “swarm ions” because they resemble swarm of bees around a beehive.

=>The area in which the ions are moving around root (or) clay particle in soils is called “oscillation zone”.

=>CEC of kaolinite increases as the pH of soil increases.

=>Total exchangeable bases (m.e/100 g.soil) % of base saturation = X 100 CEC

=>Arid region soils have high B.S than soils of humid region.

=>Soils which have higher B.S one dominated by 2:1 clay minerals like montmorillonite, vermiculite, chlorite, micas.

=>Anion exchange is more in soils high in 1:1 clay

=>Acid soils are poor in available Ca and Mg.

=>Availability of ‘S’ is not affected by soil reaction as the sulphur compounds are soluble in
whole pH range.

=>When pH is low, solubility of Fe, Mn, Al increases.

=>Availability of B, Cu, Zn is reduced when the pH is increased.

=>Availability of Mo is reduced in acid soils.

=>“Buffering” refers to resistance to slight change in pH.

=>The power to resist slight change in pH is called “buffer action”.

=>Horizons in a soil profile are broadly divided into 4 groups and are called A, B, C, D.

=>AB horizons are collectively called as ‘solum’. The solum together with parent material is
called “soil profile”.

=>“Horizon” – A layer of soil approximately parallel to the land surface.

=>The diagnostic surface horizons are called “epipedons”.

=>When larger mineral particles dominate, soil is said to be “gravelly” (or) sandy. When the
mineral colloids dominate it is “clayey”.

=>Compact soils and sandy soils have high bulk density.

=>B.D. is more in lower layers of the profile because of less O.M.

=>Addition of organic matter lowers the B. D and increases the porespace.

=>Due to leaching of Fe compounds due to high rainfall, “grey (or) grey brown” soils are formed.

=>Hue – refers to the dominant spectral colours.

=>Value – refers to the relative lightness (or) darkness of colour.

=>Chroma – relative purity of a colour.

=>“Soil consistence” is a dynamic property of soils which is expressed by the degree and kind
of “cohesion and adhesion”.

=>Non – exchangeable cations in montmorillonite – Mg, illite – K.

=>The organic matter on decomposition gets modified and acquires the properties of
“Colloids”.

=>“Soil survey” is the study and mapping of soils in their natural environment.

=>“Remote sensing” is the science and art of acquiring the information about objects from distance without physically going in contact with the object.

=>Pedalfers – Accumulation of iron – aluminium in soils under high rainfall.

=>Pedocals – Accumulation of ‘Ca’ – in areas of low rainfall

1. Alfisols – They are characterized by clay enriched Bt horizon.

2. Vertisols – These soils are black soils – Inversion of soil occurs in the profile.
3. Aridisols – These are the soils of dry regions.
4. Mollisols – These are developed under grassland vegetation.
5. Histols – These are the organic soils developed under water saturated environment.
6. Oxisols – These are very strongly weathered mineral soil.
7. Ultisols – These are the soils of low base status.
8. Spodosols – These are the mineral soils with accumulation of humus and sesquioxides.
9. Entisols – These are recently developed mineral soils horizonisation.

=>In soils, bauxite is the dominant oxide of aluminium.

=>Bluish and greenish colour of soil indicate ill drained condition.

=>The porosity and permeability of 1:1 clay mineral is high.

=>Ca & Mg have specified role of flocculation.

=>Total pore space is more in “clayey soils”.

=>Many fungi are soil inhabitants living as saprophytes on dead organic matter.

=>A larger proportion of plant nutrient present in the soil are in organic form.

=>The CEC of inorganic colloids is less than organic colloids.

=>Saline woils are dominated by chlorides and sulphates.

=>The hydrogen ion concentration of soil solution is called – Active acidity.

=>Limonite – 2Fe2O3. 3H2O.

=>Climate and biosphere are the active factors involved in the soil formation.

=>Humus theory was proposed by “von Liebig”.

=>The number of textural classes in the textural triangle is 12.

=>The steps involved in the development of soil structure are flocculation and aggregation.

=>In the arid regions with imperfect drainage, the most preferred cation for adsorption on soil
colloid is Na.

=>The soil/parent material is said to be colluvial if it is formed due to gravity.

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