Discussion
Mineral pigeonite typically occurs in the volcanic rocks because :
Answer: B
Pigeonite typically occurs in volcanic rocks because at deeper conditions it exsolves into other pyroxenes.
Pigeonite is a low-calcium clinopyroxene stable only at high temperature. In rapidly cooled lavas it is quenched and preserved. In slowly cooled plutonic rocks it does not survive: it exsolves lamellae of augite and inverts to orthopyroxene, so plutonic rocks contain 'inverted pigeonite' instead of pigeonite itself.
Pigeonite is not light enough to float in magma, and its loss at depth is due to slow cooling and exsolution rather than to pressure destabilising it or to rapid reaction with other minerals.
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