Question

Which of the following minerals is formed by decomposition of rocks leaving a residual mass of weathered material?
(A) Coal
(B) Bauxite
(C) Gold
(D) Zinc
(E) None of these

Answer 1

Hint: It is the major mineral used as an ore for the extraction of Aluminium. They are mainly found in tropical and subtropical regions where laterite soil or clay is present in abundance.

Complete answer: The mineral Bauxite is generated by decomposition of rocks that leaves a residual mass of weathered material. It is chemically an oxide of aluminium and is an important ore which is formed by both physical and chemical weathering. In physical weathering bauxites are formed by breaking down of aluminium silicate rich rocks on the earth surface. In chemical weathering, Bauxite is formed by lateralization, which is also known as tropical weathering where the laterite soil undergoes chemical reactions and forms bauxite precipitates. The quality of so formed bauxites through the weathering process depends on the location where it formed, the climate of the region, environmental features of the region, characteristics of the soil etc. Generally, the texture of Bauxite is clay-like and it can be found in various colours, particularly pink, white or red, respective of the amount of iron content present in it.

Option (A): Coal is a black sedimentary rock that is composed of carbon and hydrocarbons and it is a nonrenewable resource because of its limited amount of availability. Hence this option is incorrect.
Option (B): Bauxite is a mineral formed through chemical and physical weathering. Decomposition of rocks leaving a mass of weathered material leads to the formation of Bauxite. Thus this option is correct.
Option (C): Gold is formed by the deposition of minerals from hot fluids that flows through cracks under Earth's crust and it can be formed also by the nuclear processes such as fission, fusion and radioactive decay. Hence this is an incorrect option.
Option (D): Zinc is one of the most commonly found elements in the Earth’s crust, but it has never been found naturally as particularly in the form of metal, thus it is produced mainly through the refining process. Thus this option is incorrect.

The option (B) is correct.

Note: In industries, the extraction of Aluminium from Bauxite ore is done on a large scale through the chemical method known as the Bayer process. More than half of the Bauxite production in India is done in the state of Orissa alone.