Rocks are the chief sources for the parent materials over which soils are developed. There are three main kinds of rocks:
(i)igneous rocks,
(ii)sedimentary rocks, and
(iii)metamorphic rocks.
Igneous rocks. They are formed by the cooling, hardening and crystallizing of various kinds of lavas and differ widely in their chemical composition. They chiefly contain feldspars, maphic minerals and quartz. Rocks containing a high proportion of quartz (60-75%) are classified as acidic, whereas those containing less than 50% quartz are classified as basic. The common igneous rocks found in India are the granites(acidic) and basalts or the Deccan Trap (basic)
Sedimentary rocks. They are derived from igneous rocks and are formed by the consolidation of fragmentary rock materials and the products of their decomposition deposited by water. The common sedimentary rocks are conglomerate, sandstone, shale and limestone. Alluvial, glacial and aeolian deposits form the unconsolidated sedimentary rocks.
Metamorphic rocks. They are formed from the igneous or sedimentary rocks by the action of intense heat and high pressure or both resulting in considerable change in the texture and mineral composition. The common metamorphic rocks are gneis from granite, quartzite from quartz or sandstone, marble from limestone and slate from shale.
(i)igneous rocks,
(ii)sedimentary rocks, and
(iii)metamorphic rocks.
Igneous rocks. They are formed by the cooling, hardening and crystallizing of various kinds of lavas and differ widely in their chemical composition. They chiefly contain feldspars, maphic minerals and quartz. Rocks containing a high proportion of quartz (60-75%) are classified as acidic, whereas those containing less than 50% quartz are classified as basic. The common igneous rocks found in India are the granites(acidic) and basalts or the Deccan Trap (basic)
Sedimentary rocks. They are derived from igneous rocks and are formed by the consolidation of fragmentary rock materials and the products of their decomposition deposited by water. The common sedimentary rocks are conglomerate, sandstone, shale and limestone. Alluvial, glacial and aeolian deposits form the unconsolidated sedimentary rocks.
Metamorphic rocks. They are formed from the igneous or sedimentary rocks by the action of intense heat and high pressure or both resulting in considerable change in the texture and mineral composition. The common metamorphic rocks are gneis from granite, quartzite from quartz or sandstone, marble from limestone and slate from shale.
