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Rahul kumar Best Answer
Answer: The last two lines convey that the sandstone mainly comprises stable minerals such as Quartz, muscovite, K-feldspar etc. It happens because sandstones commonly form by the intense weathering and leaching conditions. All unstable minerals (ferromagnesium minerals) are removed by weathering. Whereas fine grains are mainly clay and ferromagnesium minerals; it happens because larger unstable mineral clasts are rapidly degraded to finer grains as a result of weathering and erosion. This is why fine grain clasts contain relatively unstable minerals.