(a) Sedimentary rock is the type of rock formed from the accumulation of layers of deposits of sediments in water or on land. These sediments later join or cement together in layers to form sedimentary rock.
Two processes of sedimentary rock formation are:
(i) Mechanical Process: Involves the formation of sedimentary rock from sediments accumulated from other rocks such as igneous and metamorphic rocks. These rocks settled in layers to form sedimentary rock E., J, formation of sandstone, shale, conglomerate.
(ii) Chemical Process: Pre-existing igneous and metamorphic rocks are precipitated chemically from solution of one kind or the other. Rock salt are derived from strata which once formed the beds of seas or lakes. Examples of rocks formed by chemical process include sodium chloride, gypsum, etc.
(b) Three ways in which sedimentary rocks are important to man are:
(i) Some sedimentary rocks are sources of some useful minerals such as coal and petroleum which serve as fuel energy to man.
(ii) Some sedimentary rocks are used for road construction and for building houses.
(iii) Rock salt, e.g sodium chloride (table salt) is a source of body mineral needed for maintaining osmotic pressure in the blood.