Question

Primary rocks that are of thermal origin are ?
a. Metamorphic rocks
b. Sedimentary rocks
c. Igneous rocks
d. None of these

Answer 1

Hint:
Primary rock is an introductory term in geology, which refers to the first crystalline rock formed in geologic time, which does not contain any biological remains, such as granite, gannis, and schist, as well as igneous from all ages and magmatic structures.

Complete solution:
Igneous rock or magmatic rock, is one of the three main rock types, which are sedimentary and metamorphic. Igneous rock is cooled and formed only through solidification of magma or lava.

Magma can be obtained from partial melting of existing rocks, either from a planet's particle or crust. Typically, melting is caused by more than one or three processes: an increase in temperature, a decrease in pressure, or a change in composition. The freezing of the rock occurs either as intrusive rocks below the surface or as external rocks on the surface. Igneous rock can be used as granular, crystalline rocks with or without crystallization to form natural glass without crystallization. Igneous rocks occur in a wide range of geological settings: shields, platforms, organisms, basins, large igneous provinces, elongated crusts, and oceanic crusts.

Igneous rocks are also important geologically because:

- Their mineralogy and global chemistry give information about the composition of the lower crust or upper mantle from which their original magma was extracted, and the temperature and pressure conditions that allow this extraction.

- Their absolute ages can be derived from various forms of radiometric dating and can be compared to adjacent geological strata, thus allowing the calibration of geological time scales.

- Their characteristic square measure is sometimes characteristic of a particular tectonic atmosphere, permitting tectonic reconstruction.

 - In bound special circumstances they host vital mineral deposits for instance, tungsten, tin and metallic element square measure sometimes related to granite and igneous rock, whereas ores of atomic number 24 and atomic number 78 square measure something related to gobbos.

Hence, the correct answer is option C.

Note:
Igneous and metamorphic rocks make up 90–95% of the top 16 kilometers of the Earth's crust by volume. Igneous rocks are about 15% of the Earth's present land surface. Most of Earth's oceanic crusts are made of igneous rock.