Some important MCQs with explanations related to Petrology for the Jharkhand Academic Council (JAC) 12th Exam -1

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1. Which of the following rocks is an igneous rock?

a) Granite
b) Sandstone
c) Marble
d) Quartzite

Answer: a) Granite
Explanation:
Igneous rocks form from the solidification of magma or lava. Granite is an intrusive igneous rock formed when magma cools slowly inside the Earth. Sandstone is sedimentary, and Marble and Quartzite are metamorphic rocks.


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2. Which process is responsible for the formation of sedimentary rocks?

a) Crystallization
b) Lithification
c) Melting
d) Metamorphism

Answer: b) Lithification
Explanation:
Sedimentary rocks form through the process of lithification, where sediments are compacted and cemented over time. Crystallization is associated with igneous rocks, and metamorphism forms metamorphic rocks.


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3. What type of texture is commonly found in volcanic igneous rocks?

a) Coarse-grained
b) Porphyritic
c) Glassy
d) Foliated

Answer: c) Glassy
Explanation:
Volcanic igneous rocks cool quickly on the Earth's surface, leading to the formation of glassy textures (e.g., obsidian). Coarse-grained textures are typical of intrusive igneous rocks, and foliated textures are found in metamorphic rocks.


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4. Which rock is known as the "Parent Rock" for Marble?

a) Sandstone
b) Shale
c) Limestone
d) Granite

Answer: c) Limestone
Explanation:
Marble is a metamorphic rock formed by the metamorphism of Limestone under heat and pressure. Sandstone and Shale metamorphose into Quartzite and Slate, respectively.


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5. What is the main mineral composition of Basalt?

a) Quartz and Feldspar
b) Calcite and Dolomite
c) Pyroxene and Plagioclase
d) Muscovite and Biotite

Answer: c) Pyroxene and Plagioclase
Explanation:
Basalt is a mafic igneous rock rich in minerals like pyroxene and plagioclase. Quartz and feldspar are common in granite, while calcite and dolomite are typical of sedimentary rocks like limestone.


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6. Which of the following is a clastic sedimentary rock?

a) Limestone
b) Sandstone
c) Coal
d) Marble

Answer: b) Sandstone
Explanation:
Clastic sedimentary rocks form from fragments of pre-existing rocks. Sandstone is made of compacted sand particles. Limestone is a chemical/organic sedimentary rock, and coal is organic.

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7. What is the characteristic feature of metamorphic rocks?

a) Foliation
b) Vesicles
c) Bedding planes
d) Porosity

Answer: a) Foliation
Explanation:
Foliation refers to the alignment of minerals in metamorphic rocks, giving them a layered appearance. Vesicles are found in igneous rocks, and bedding planes are features of sedimentary rocks.


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8. The Deccan Traps in India are made of which type of rock?

a) Granite
b) Basalt
c) Shale
d) Gneiss

Answer: b) Basalt
Explanation:
The Deccan Traps are large igneous provinces in India formed by extensive volcanic eruptions. They primarily consist of basalt, an extrusive igneous rock.


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9. Which rock type is most likely to contain fossils?

a) Igneous rocks
b) Sedimentary rocks
c) Metamorphic rocks
d) All of these

Answer: b) Sedimentary rocks
Explanation:
Fossils are primarily found in sedimentary rocks like limestone and shale, as these rocks form from sediments that often preserve remains of organisms.


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10. Which type of metamorphism occurs due to heat from a nearby magma body?

a) Regional metamorphism
b) Contact metamorphism
c) Dynamic metamorphism
d) Hydrothermal metamorphism

Answer: b) Contact metamorphism
Explanation:
Contact metamorphism occurs when rocks come into contact with heat from nearby magma, leading to changes in texture and mineral composition. Regional metamorphism involves both heat and pressure over large areas.

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