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General Studies 2022 GS Paper I 10 marks 150 words Compulsory Describe

GS Paper I — Q4

Describe the characteristics and types of primary rocks. (Answer in 150 words) 10

हिंदी में प्रश्न पढ़ें

प्राथमिक चट्टानों की विशेषताओं एवं प्रकारों का वर्णन कीजिए। (150 शब्दों में उत्तर दें)

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Model answer

Written by UPSC Answer Check against this question's marking rubric, to the 150-word length. UPSC does not publish answers for Mains — this is one way to score well, not an official key.

Primary rocks are igneous rocks formed by the cooling and solidification of magma or lava; they are the parent rocks from which sedimentary and metamorphic rocks derive. They are generally crystalline, hard and massive, lack fossils and stratification, and contain chemically active ferromagnesian minerals such as olivine and pyroxene, while quartz is chemically resistant. Their texture records cooling history: intrusive/plutonic rocks cool slowly beneath the surface and develop coarse, phaneritic grains, including granite, syenite, diorite, gabbro and peridotite. Extrusive/volcanic rocks cool rapidly at the surface, producing fine-grained, aphanitic or glassy textures, including basalt, andesite, rhyolite, obsidian and pumice. In India, Deccan Trap basalt is the world’s largest flood basalt, and granites occur in Rajasthan/Gujarat; Tamil Nadu’s charnockite is metamorphic, not primary. Thus primary rocks constitute the fundamental framework of the crust and record tectonic and volcanic history, and are essential for geological mapping and mineral exploration.

What "Describe" is asking you to do

Give a full, ordered account of the thing named — its parts, stages or mechanism — in the sequence in which it actually exists or occurs. Most describe questions come from the science optionals, where the marks sit in correct technical detail and, where the stem says so, a labelled diagram.

Structure that answers it

One-line identification of the subject → the parts or stages in their real order, each with its defining detail → labelled diagram where the subject is structural → closing line on function or significance

Where marks are lost

Loose general prose where the examiner is ticking named parts, correct terminology and their sequence; and in the General Studies papers, turning to evaluation before the description is finished.

All UPSC directive words, compared →

How this answer will be evaluated

Approach

Framework: Geography: explain the mechanism, then location follows. describe: define > structure or process in order > labelled diagram > significance Full marks: Clear definition, distinct mechanism, and accurate classification with examples.

Key points expected

  • Define primary rocks as igneous rocks formed from cooling magma.
  • Explain the mechanism of solidification of molten material.
  • Classify into intrusive (plutonic) and extrusive (volcanic) types.
  • Distinguish between intrusive and extrusive based on cooling rate.

Evaluation rubric

Each sub-part is marked on its own, against the marks and word limit printed on the paper.

  1. The answer Define primary rocks and detail their formation process and classification. 10 marks · 150 words

    describe— define → structure or process in order → labelled diagram → significance

    Must cover

    • Define primary rocks as igneous rocks formed from cooling magma.
    • Explain the mechanism of solidification of molten material.
    • Classify into intrusive (plutonic) and extrusive (volcanic) types.
    • Distinguish between intrusive and extrusive based on cooling rate.

    Loses marks

    • Confusing primary rocks with sedimentary or metamorphic rocks.
    • Narrating geological history instead of describing rock characteristics.
    • Failing to distinguish between intrusive and extrusive types.

    Earns more

    • Mention specific examples like granite or basalt.
    • Note the interlocking crystal structure of intrusive rocks.
    • Reference the 'Joints' or 'Columnar' structures in basalt.
    • Mention the lack of fossils in primary rocks.

    Extra mark

    • 30-second sketch map showing intrusive vs extrusive formation.
    • Mention specific mineral composition (e.g., silica content).

Practice this exact question

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