A volcanic rock consisting of alkali feldspar (70%), sodic plagioclase (10%) and nepheline (20%) is named as
Show Hint
- Phonolite
- Tephrite
- Trachyte
- Andesite
The Correct Option is A
Solution and Explanation
Step 1: Understanding the composition of volcanic rocks.
Phonolite is a volcanic rock with a composition rich in alkali feldspar and nepheline. It typically contains more than 60% alkali feldspar and a substantial amount of nepheline.
Step 2: Analyzing the options.
(A) Phonolite: Correct — Phonolite is characterized by a composition of alkali feldspar and nepheline, as described.
(B) Tephrite: Tephrite is a basaltic rock that contains a higher proportion of plagioclase than phonolite.
(C) Trachyte: Trachyte is similar to phonolite but contains less nepheline.
(D) Andesite: Andesite is an intermediate volcanic rock, not matching the given composition.
Step 3: Conclusion.
The correct answer is (A) Phonolite.
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