A sandstone has<5% matrix. The recalculated modal compositions of feldspar, quartz, and rock fragments are 45%, 35%, 20%, respectively. The sandstone is classified as
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- feldspathic wacke
- quartz wacke
- lithic arkose
- subfeldsarenite
The Correct Option is A
Solution and Explanation
The question provides the mineralogical composition of a sandstone with a matrix of less than 5%. The classification depends on the proportion of feldspar, quartz, and rock fragments.
Step 2: Analyzing the options.
(A) feldspathic wacke: Correct — With 45% feldspar, this sandstone is classified as feldspathic wacke, which contains more feldspar than quartz or lithic fragments.
(B) quartz wacke: This would be the case if the sandstone contained mostly quartz, but here feldspar is the dominant component.
(C) lithic arkose: This classification is incorrect because arkose is more typical of sandstones with a high percentage of feldspar and less rock fragments.
(D) subfeldsarenite: This is an incorrect term for this classification.
Step 3: Conclusion.
The correct answer is (A) feldspathic wacke, as it has a high percentage of feldspar.
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