Introduction
The Materials of crust or lithosphere is Called rocks. The smallest components of the earth’s crust is Called elements. As regards to earth the eight most abundant elements of earth are (iron, oxygen, silicon, Magnesium, nickel, sulphur, Calcium and ammonium) constitute 99% of the total mass of the earth whereas only four elements (iron, oxygen, Silicon and magnesium) account for 90% of the total mass of the earth. On the other hand, the eight most abundant elements which constitute 99% of total mass of the Crust are oxygen, silicon, aluminum, iron, magnesium, Calcium, Potassium, and Sodium.
Table 1 Whole Earth
Elements |
Percentage |
Iron |
35 |
Oxygen |
30 |
Silicon |
15 |
Magnesium |
13 |
Nickel |
2.4 |
Sulphur |
1.9 |
Calcium |
1.1 |
Aluminium |
1.1 |
Others,less than |
1.0 |
Table 2 Earth’s Crust
Elements |
Percentage |
Oxygen |
46 |
Silicon |
28 |
Aluminium |
8 |
Iron |
6 |
Magnesium |
4 |
Calcium |
2.4 |
Potassium |
2.3 |
Sodium |
2.1 |
Others, lessthan |
1.0 |
More than one elements of the earth’s crust are organized to form Compounds which are known as minerals and minerals are organized to form rocks. The important mineral groups are silicates, Carbonates, Sulphides, metal oxide etc.
The Silicate Minerals
These are very important rock making minerals. The most outstanding rock forming silicate mineral groups are quartz, feldspar and ferromagnesium.Quartz is composed of two elements viz. silicon and oxygen and is generally a hard and resistant mineral .The most abundant and the most important rock forming silicate mineral is feldspar which is also very important economically because it is used in ceramics and glass industry. Feldspar is very weak mineral and is easily broken down due to Chemical weathering and is changed into Clays as hydrated alumino silicates. When silicon and oxygen combine with iron and magnesium, ferromagnesium minerals formed. Ferromagnesium minerals are easily weathered and are eroded away .The rocks having abundant ferromagnisium minerals Provide weak structure for the Construction of of building roads, dams, reservoirs etc.
Carbonate Group of Minerals
This group of minerals is very much susceptible to chemical weathering and erosion in humid areas. Calcite is the most important mineral of this group. Limestones and marbles having abundant Calcite are corroded by the surface and the groundwater and extensive Caves are formed below the ground surface. Such areas provide very weak structures for construction sites.
Sulphide Minerals
Includes Pyrites, iron Sulphides etc. when these minerals come in Contact with water or air, these form ferric hydroxides and sulfuric Acids which causes serious environmental problems.
Metallic elements
Iron, Aluminium etc. after reacting with atmospheric oxygen form metal oxides which are commercially Very important.
Rocks, thus, representing the geomaterials of the earth’s crust, are composed of two or more minerals.
Classification of Rocks
Rock Cycle
‘The landscape is a function of structure, process and time (stages)’-W.M.Davis
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