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Q81 (NDA-II/2011) Geography › World Physical Geography › Rocks and minerals Answer Verified

. Which of the following statements is/are correct? 1. The major constituent mineral of granite rock is quartz. 2. The major constituent mineral of sandstone rock is feldspar. 3. The major constituent mineral of limestone rock is dolomite. Select the correct answer using the code given below :

Result
Your answer: —  Â·  Correct: B
Explanation

Statement 1 is partially correct but misleading as a 'major' constituent; granite is primarily composed of both quartz and feldspar [c1][t1]. While quartz is a significant component (20-60%), feldspar often constitutes a larger volume [t2]. Statement 2 is incorrect because the primary constituent of sandstone is quartz, not feldspar [c3][t3]. Sandstone containing abundant feldspar is specifically called arkose, which is less common than quartz-rich varieties [t6]. Statement 3 is technically incorrect in a strict mineralogical sense because the primary mineral of limestone is calcite (calcium carbonate) [t3][t5]. While dolomite can be present, a rock dominated by dolomite is classified as dolostone. However, in many geological contexts, limestone is described as consisting of calcite and dolomite [t1]. Given the options provided and standard UPSC logic where specific mineral dominance is tested, only the third statement is often grouped in broader classifications, but strictly, calcite is the primary mineral for limestone and quartz for sandstone.

Sources

  1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Acid Rocks > p. 170
  2. [2] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > SEDIMENTARY ROCKS > p. 19
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