Final answer:
The described rock is vesicular and fine-grained, indicative of a volcanic origin and rapid cooling. It is likely basalt, which is the fine-grained equivalent of gabbro and is characterized by small vesicles from trapped gas bubbles.
Step-by-step explanation:
The question seems to describe a type of volcanic rock that is fine-grained and vesicular, which implies that it contains small cavities or vesicles that were formed by trapped gas bubbles during the solidification of the rock. Given the description of 'fine-grained equivalent of gabbro,' the rock in question is likely to be basalt.
Basalt is a common extrusive igneous rock that is typically dark grey to black, often characterized by a vesicular texture due to its volcanic origin and rapid cooling, which traps gas bubbles within the rock.
This fine-grained nature contrasts with the coarse-grained nature of gabbro, its intrusive counterpart, which cools slowly beneath the Earth's surface, allowing for the growth of larger crystals.