What does this texture indicate about the formation of this rock?

Question

Quizplus · Accepted Answer

The texture shown in the image suggests that the rock is a porphyritic one, meaning that it has two distinct crystal sizes - larger ones (phenocrysts) and smaller ones (groundmass). This indicates that the magma had already started to cool and form crystals before rising closer to the surface and undergoing further cooling to solidify into a rock. The presence of a groundmass suggests that the cooling process may not have been too rapid, eliminating option A (explosive pyroclastic eruption) and D (abundant dissolved gas) as possible answers. Option B (rock solidifying at great depth) is also unlikely as the texture suggests that the rock formed from magma cooling relatively quickly after rising closer to the surface.

What Does This Texture Indicate About the Formation of This