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QUESTION 4
GS1
10 marks

Describe the characteristics and types of primary rocks.

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7 min
150 words
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What the examiner wants

Describe the defining traits of primary (igneous) rocks and classify them by origin and composition with examples.

DescribeGive a clear, detailed account of the main features.

Demand-wise check

  1. 1Characteristics: formed from cooling magma or lava, crystalline, no fossils, generally hard and non-layered≈35 words
  2. 2Types by place of formation: intrusive (plutonic, hypabyssal) and extrusive (volcanic)≈35 words
  3. 3Types by composition: acidic (granite) and basic (basalt), with Indian examples≈35 words

Open in about 20 words and close in about 20.

Answer plan

DefinitionKey characteristicsClassification by originClassification by compositionIndian examples and economic use

Where marks usually go

  • Confusing primary rocks with sedimentary layers
  • Listing types without examples such as granite, basalt, gabbro

Draw this

  • Diagram of intrusive bodies (batholith, laccolith, sill, dyke) and a lava flow

Value addition

  • Indian exampleThe Deccan Traps are basaltic lava flows (extrusive, basic) covering a large part of western and central India.Geological Survey of India
  • Indian exampleGranite of the Peninsular gneissic complex is used widely as building stone in Karnataka, Tamil Nadu and Andhra Pradesh.Geological Survey of India

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