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 lithic arkoses having a significant amount of feldspar and rock fragments.

Answer 1

The Correct Option is C

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: This classification is incorrect because feldspathic wacke typically has more feldspar than the quartz or lithic fragments, but here the feldspar proportion is 45%.
(B) quartz wacke: This would be the case if the sandstone contained mostly quartz, but here feldspar is the dominant component.
(C) lithic arkose: Correct — Lithic arkose has a significant proportion of feldspar, and it contains a fair amount of rock fragments, making this the correct classification for this sandstone.
(D) subfeldsarenite: This is an incorrect term for this classification.
Step 3: Conclusion.
The correct answer is (C) lithic arkose, as it has a high percentage of feldspar and rock fragments.