Read this article to learn about Soil Types: Igneous, Sedimentary and Metamorphic Rocks!
Rocks are generally classified into three types on the basis of their origin and structure.
These are as under:
(1) Igneous rocks,
(2) Sedimentary rocks,
(3) Metamorphic Rocks
1. Igneous Rocks:
These are formed by cooling and solidification of molten magma or lava which escapes through fissures from the interior of the earth. The solidification may occur at great depths resulting in the plutonic rocks, or at moderate depthinthe earth forming the so-called intrusive rocks or on the surface of the earth forming the extrusive or effusive rocks. Extrusive rocks are formed as a result of volcanic activities. Important igneous rocks involved in the weathering process are Granite, Basalt, Gabbro Diabase, Syenite, Andesite etc. They are composed of primary minerals such as quartz, feldspars and biotite, augite and hornblende.
2. Sedimentary Rocks:
These develop due to gradual accumulation and consolidation of weathering product or mineral particles brought by wind or water on the surface of earth. Such rocks are characterised by the presence of distinct sediments or layers in them. Some examples of sedimentary rocks are limestone, shale, conglomerate, clays, quartz and dolomite are the common dominant mineralsinthem. Sedimentary rocks do not weather as rapidly as the igneous rocks.
3. Metamorphic Rocks:
These are formed after transformation of igneous and sedimentary rocks when they are subjected to intense heat and pressure and are influenced chemically by active and gases. Important metamorphic rocks which take part in weathering process are formed from shale’ marble (formed from limestone), schist(formed from shale) and quartzite (from sandstone). Dominant minerals are quartz, clays and calcite.
Wallwork (1970) has summarized the details of the principal soil forming rocks in Table 22.2: