Answer:
The rock containing clinopyroxene and plagioclase (a type of feldspar) is called either basalt (fine grained extrusive rock) or gabbro (coarse grained intrusive rock). The plagioclase is generally calcium rich i.e. anorthite rich. But rock contains sodium rich feldspar. This means the sodium has replaced calcium. This replacement occurs in underwater (in oceans/seas) extrusion of basalt where sodium from seawater replaces the calcium in anorthite rich plagioclase feldspar. The altered basalt due to sodium exchange is called spilite which contains sodium rich feldspar and pyroxene.
Explanation:
