What are the three common types of pyroclastic volcanic rock? How to tell the difference between them?

-Tuff: Mostly Rhyolite, very porous, lots of cavities and bubbles, many different rock fragments and crystals (the matrix is almost white, the phenocrystals are multi-colored) -Pozzolan: Very porous, some small bubbles and cavities, texture has layers, some crsytals and rock fragments. -Bentonite: Clay-like due to weathering, usually white, light blue, yellow or green. Extremely fine grain, ashy.