What type of volcanic rock is characterized by its light, sponge-like texture and gas bubbles?

Pumice is a type of volcanic rock known for its light, sponge-like texture, which is a result of the rapid cooling and depressurization of volcanic lava that is rich in gas bubbles. During the eruption process, gas trapped in the lava expands and creates a frothy, porous structure as it solidifies. This unique texture not only makes pumice very lightweight but also allows it to float on water.

In contrast, basalt, which is also a volcanic rock, has a dense and fine-grained texture due to the rapid cooling of lava but lacks the significant gas bubble structure that characterizes pumice. Obsidian is a volcanic glass that forms when lava cools so quickly that crystals do not have time to form, resulting in a smooth, glassy appearance rather than a porous texture. Tuff, on the other hand, is formed from volcanic ash and rock fragments that have been compacted together, and it does not possess the same spongy quality as pumice.

Thus, pumice is distinguished by its unique characteristics and the processes of its formation, making it the correct answer.