Question

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

• A. feldspathic wacke
• B. quartz wacke
• C. lithic arkose
• D. subfeldsarenite

Hint:

Sandstones are classified based on their mineral composition, with feldspathic wackes containing more feldspar than quartz or lithic fragments.

Answer 1

The Correct Option is A

Step 1: Understanding the question.
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.