Final answer:
Rhyolite is an igneous rock with an aphanitic texture that is the extrusive equivalent of granite. It often presents a porphyritic texture, with larger crystals (phenocrysts) embedded in a fine-grained matrix and can come in various colors.
Step-by-step explanation:
The rock described in the question is likely to be rhyolite, which is the fine-grained equivalent of granite and has an aphanitic texture. Rhyolite's fine grain size comes from the rapid cooling of high-viscosity lava, resulting in very small crystals that are less than 1 mm in size. This rock can exhibit a variety of colors, commonly including gray, pink, and sometimes red with black. Rhyolite may also exhibit a porphyritic texture, indicating that it contains larger crystals, also known as phenocrysts, embedded within its finer-grained matrix.