For 10 points, name this light colored spongy rock often used in concrete, but better known as a powder or an abrasive.
When combined with calcium hydroxide, this rock is called pozzolan and has industrial uses as a form of cement. This rock can form a namesake cone around volcanoes that is similar to a cinder cone, but is filled with vesicles. These igneous rocks are formed when lava high in (*) volatiles cools quickly above ground and are sometimes given the name "volcanic froth," and they are one of the few rocks to float in water.  For 10 points, name this light colored spongy rock often used in concrete, but better known as a powder or an abrasive.
When combined with calcium hydroxide, this rock is called pozzolan and has industrial uses as a form of cement.
{Pumice}