Gerard LEwkawich, age 12, of Winnipeg, Canada, for his question:

What is Pumice stone?

When you toss a stone into a pond, you expect it to sink, because stones are much heavier than water.  But this fact does not apply to certain samples of pumice stone.  These 1ighter than water stones will float on the surface.  They look and they feel like pebbles of frozen foam, and in a way: that is just what they axe

Pumice starts out as lava, from an erupting volcano.  Its minerals are like those in solid granite.  but the molten mixture is frothy with bubbles of gas. The hot, foamy mixture cools rapidly in the air and becomes solid before the frothy bubbles have had time to escape.  And the solid pumice stone is full of tiny holes, which make it light enough to float on the water.