What makes a pumice rock different from granite and rhyolite??

All these rocks have the same composition, but they have different texture. Granite is a plutonic rock so it is formed by well crystallized mineral, contain no gl, no vessicles. Rhyolite contain some small crystal, abundant gl, but no vessicles (gas bubbles). Pumice is formed mostly by gl with abundant vessicles, so much gas bubbles in fact that is less dense than water.