Question:
Identify the rocks P and Q in the diagram as per the IUGS classification.
Identify the rocks P and Q in the diagram as per the IUGS classification.
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In the IUGS classification, the key is to identify the mineral composition of the rocks, particularly the ratios of olivine, pyroxenes, and other minerals.
Updated On: Dec 14, 2025
- P – Webstetite, Q – Wehrlite
- P – Dunite, Q – Webstetite
- P – Webstetite, Q – Dunite
- P – Harzburgite, Q – Wehrlite
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The Correct Option is D
Solution and Explanation
The ternary diagram is Olivine–Orthopyroxene–Clinopyroxene (IUGS ultramafic classification).
Key fields:
Dunite: >90% olivine
Harzburgite: Olivine + orthopyroxene (low clinopyroxene)
Wehrlite: Olivine + clinopyroxene (low orthopyroxene)
Websterite: Orthopyroxene + clinopyroxene (low olivine)
Point P
Lies near the olivine–orthopyroxene side, with high olivine but very little clinopyroxene
→ Harzburgite
Point Q
Lies near the olivine–clinopyroxene side, with significant clinopyroxene and olivine, little orthopyroxene
→ Wehrlite
Answer: (D)
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