Question

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

Answer 1

Hint:
The molded rocks are made from the molten rock called Magma. They are called primary rocks because they start the rock chakra. Other rocks are made from these rocks. This is the reason that these rocks are often known as original rocks.

Complete answer:
Primary rocks which are of thermal origin are called igneous rocks.

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 causes 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 marine crusts.

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. 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 characteristics are typically characteristic of a specific tectonic environment, allowing tectonic reconstruction.

- In certain special circumstances they host important mineral deposits (ores): for example, tungsten, tin, and uranium are usually associated with granite and diorite, while ores of chromium and platinum are usually associated with gabbros.

Hence, the correct answer is option C.

Note:
Earth's crust averages about 35 kilometers below the continents, but averages only 7-10 kilometers below the oceans. The continental crust is composed mainly of sedimentary rocks, resting on a great metaphor including granite and granite and a crystalline basement made of a great variety of igneous rocks. The oceanic crust is mainly composed of basalt and gabbro. Both continental and oceanic crusts rest on continental peridotites.