which mineral assemlage and relative abundaces are typical of gabbro and basalt?

Question

olivine/pyroxene/amphibloe or
biotite/muscovite/amphibole?

Answer 1

Basalt is the extrusive equivalent of gabbro, therefore both of these rock types have equivalent mineral assemblages consisting of plagioclase (a feldspar) and pyroxene, and possibly olivine and magnetite. You will not find biotite or muscovite in basalt or gabbro, so the best answer from your two choices is "olivine/pyroxene/amphibole".

As for abundances, that depends on whether the rock is tholeiitic or alkali, but in general you can look for 60% plagioclase, 35% pyroxene, and 5% accessory minerals such as magnetite and augite.

Answer 2

Because Gabbro and Basalt have the same composition and vary only in crystal size, it is fair to say that they have the same mineral assemblages and relative abundances--the guy above me is correct.

He is also correct in stating that they are typically composed of olivine, pyroxene, and amphibloe because they are mafic.

Answer 3

olivine/pyroxene/amphibole