Final answer:
Rhyolite porphyry is an igneous rock with an aphanitic texture and porphyritic pattern due to its large phenocrysts within a fine-grained groundmass. It is commonly light gray, pinkish, or reddish, and contains felsic minerals such as quartz and potassium feldspar.
Step-by-step explanation:
Rhyolite porphyry is a type of igneous rock known for its aphanitic texture, which means it has crystals that are generally less than 1 mm in size and are too fine to identify with the neked eye. The color of rhyolite can vary from light gray to pinkish or somewhat reddish hues.
In terms of mineral content, rhyolite is felsic and includes minerals such as quartz, potassium feldspar, and sometimes mica. Porphyritic rhyolite has larger crystals, known as phenocrysts, embedded within a finer-grained matrix, giving it a distinct appearance.
When examining rhyolite porphyry, one can expect a texture that includes both fine-grained groundmass and larger phenocrysts if present.
The rock is typically very hard but may become crumbly if weathered. Due to its high silica content, rhyolite serves as a good indicator of explosive volcanic activity, as its high viscosity tends to trap gases leading to powerful eruptions.