(a) Enumerate four economic importance of rocks: (i) to man; (ii) in agriculture. (b) State two characteristics of each of the following (1) igneous rock (ii) metamorphic rock. (c) Describe the mode of formation of sedimentary rocks.
Explanation
(a) Economic importance of rocks: (i) To man:
(1) Used as grinding and sharpening stones.
(2) Used for breaking hard kernels and other hard seeds.
(3) Precious minerals are mined from rocks.
(4) When polished, rocks like marble and gemstones are used for decorative purposes and as jewellery.
(5) Organic rocks like peat, coal and lignite are sources of fuel.
(6) Salt-based rocks like sodium chloride and potassium chloride supply minerals used in cooking food, e.g. table salt and potash.
(7) Rocks such as granite and limestones are used for construction, e.g. roads, buildings, etc.
(8) Rocks are used as centers of tourism, e.g. Olumo rock.
(9) For research purposes.
(ii) In Agriculture:
(1) Soil formation.
(2) Used for farm roads and building construction.
(3) Used to reduce soil erosion.
(4) Used for sharpening farm tools like knives and cutlasses.
(5) Used for breaking hard kernels and seeds.
(6) Used as grits in livestock feed formulation.
(7) Used in fertilizers blending.
(8) Rocks containing calcium and magnesium are used as liming materials.
(9) As feed additives, e.g. salt lick.
(10) Source of plant nutrient (mica releases potassium).
(b) Characteristics of rocks: (i) Igneous rock: (1) They are crystalline in nature. (2) Some have little holes on the surface e.g. pumice rock. (3) Some may be massive. (4) They are very hard.
(ii) Metamorphic rock: (1) They are multi-coloured. (2) They are granular. (3) They may be massive. (4) They are hard. (5) May contain fossils. (6) Sometimes show the appearance of igneous or sedimentary rocks.
(c) Description of the mode of formation of sedimentary rocks:
(1) Derived from pre-existing rocks of all types/dissolved minerals/organic materials.
(2) The disintegrated materials are moved from site of origin and deposited elsewhere by agents such as water, glacier, wind, etc.
(3) The particles are deposited in layers/strata.
(4) Cemented together by colloidal materials, e.g CaCO3, silica, iron oxides, mineral gellies, etc.