Question

A coarse-grained igneous rock consists of 55% olivine, 25% augite, and 20% enstatite. According to the IUGS classification, the rock is

• A. websterite
• B. lherzolite
• C. wehrlite
• D. harzburgite

Hint:

In the IUGS classification of igneous rocks, lherzolite is characterized by its high olivine content, typically around 50% or more, along with significant pyroxenes like augite and enstatite.

Answer 1

The Correct Option is B

The IUGS classification system for igneous rocks is based on the mineral composition of the rock. In this case, the rock consists of:
- 55% olivine,
- 25% augite (a pyroxene),
- 20% enstatite (another type of pyroxene).
According to the classification, when the rock contains olivine, augite, and enstatite, it typically falls under the category of lherzolite. This rock is a type of peridotite, which is an ultramafic rock. Lherzolite is characterized by a higher percentage of olivine compared to other related rocks like harzburgite, which contains less olivine and more pyroxenes.
Thus, the correct answer is (B) lherzolite.