Discussion
An ultrabasic rock consisting of phenocrysts of olivine and minor pyroxene in a groundmass of diopside and kalsilite with small amounts of perovskite, olivine and biotite :
Answer: C
The rock is mafurite.
Mafurite is a rare ultrapotassic volcanic rock from the Toro-Ankole field of south-west Uganda. It consists of olivine and pyroxene phenocrysts in a groundmass of clinopyroxene and kalsilite, with minor perovskite and biotite. The presence of kalsilite, a potassium feldspathoid, with no feldspar, is its defining feature.
Katungite, from the same region, is an olivine melilitite in which melilite takes the place of kalsilite. Kimberlite is an olivine-rich breccia with phlogopite and carbonate but no kalsilite groundmass, and pyroxenite is a plutonic rock of pyroxene alone.
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