What distinguishes basalt from other volcanic rocks?

Basalt is primarily distinguished from other volcanic rocks by its composition and physical characteristics, particularly its texture. The presence of gas bubbles is significant, as basalt often forms from lava that has erupted at the surface and cooled quickly. During this rapid cooling, gas can become trapped in the solidifying lava, leading to the formation of vesicles—small cavities or bubbles in the rock. This textural feature is a key characteristic that differentiates basalt from other volcanic rocks, which might not exhibit this level of gas-induced porosity.

While other volcanic rocks, such as pumice, can also have gas bubbles, the context of basalt specifically emphasizes the manner in which these bubbles can affect its overall texture and density. Other characteristics mentioned, like the presence of abundant quartz or light color, do not apply to basalt as it typically lacks quartz and is, in fact, usually dark. Moreover, basalt's porosity can vary, but it is not universally characterized by high porosity like pumice or scoria. Thus, the presence of gas bubbles serves as a distinct identifier for basalt among volcanic rocks.