Question

Which of the following is called ‘primary rocks’?
(A) Metamorphic rocks
(B) Sedimentary rocks
(C) Igneous rocks
(D) Stratified rocks

Answer 1

Hint: Rocks are a hard material made up of one or more minerals. Minerals are naturally occurring solid inorganic substances having definite chemical composition and physical properties. Monomineralic refers to composed of one mineral and polymineralic is composition of two or more minerals.

Complete step by step solution
Rocks are found in earth’s mantle and crust. Rocks are generally changing. The rock cycle is the process by which new rock forms from old rock materials. Rocks are geologically classified into igneous rock, sedimentary rock, metamorphic rock.

Rock cycle
1. Equilibrium
2. Interrelationship between- igneous rocks, sediment, sedimentary rocks, metamorphic rocks, weathering and erosion.

Types
1. Igneous rocks- formed by the cooling and solidification of magma (molten rocks). It begins the rock cycle. So, it is known as primary rocks. The categories of igneous rocks are extrusive and intrusive. Examples of igneous are pumice. Scoria, granite, obsidian.
2. Sedimentary rocks- formed by the composition and cementation of layers of sediments (rock, fragments, organic remain, chemical deposition). Examples of sedimentary rocks are conglomerate, shale, sandstone, gypsum, limestone.
3. Metamorphic rocks- formed when existing rocks are changed by intense heat and pressure. It does not melt. Examples of metamorphic rocks are gneiss and schist.

Thus the option (C) is correct

Note Rocks are divided based on three major factors, they are geological classification, physical classification, chemical classification, chemical classification. Physical classification is classified into stratified rocks, Unstratified rocks, foliated rocks. Chemical classification is classified into argillaceous rocks, calcareous rocks, siliceous rocks.