Discussion
Match the following rock types with their essential mineral composition :
| Rock | Essential Mineral |
|---|---|
| (a) Monzonite | (i) Potash feldspar + plagioclase |
| (b) Norite | (ii) Labrodorite + orthopyroxene (enstatite, hypersthene, bronzite) |
| (c) Picrite | (iii) Olivine + augite + Calc-plagioclase |
| (d) Rhyolite | (iv) Quartz + alkali feldspar \(\gt\) plagioclase |
Answer: D
The correct matching is (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv).
- Monzonite has roughly equal potash feldspar and plagioclase.
- Norite is a gabbroic rock of calcic plagioclase (labradorite) with orthopyroxene such as hypersthene.
- Picrite is an olivine-rich basaltic rock with augite and calcic plagioclase.
- Rhyolite is the volcanic equivalent of granite: quartz with alkali feldspar exceeding plagioclase.
Option A gives monzonite the norite assemblage, option B gives rhyolite the monzonite assemblage, and option C gives monzonite the rhyolite assemblage.
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