Richard Savoles, age 11, of Albany, New York, for his question:

How did the holes get into pumice stone?

Pumice stone is rough and usually pale, pearly grey. It is a light weight stone and feels like a feather in your hand. The rough stone is riddled with holes like bubbles. Under a magnifying glass you can see still smaller bubbles in the stone. In fact, a lump of pumice stone seems to be a gob of frozen foam.

And this is just what it is. Pumice is a lava stone, born in a seething volcano. Down below the ground it was part of a pool of magma, a deep reservoir of molten rock and gases. The volcano erupted and poured a river of this boiling bubbling mixture down its sloping sides.

Sometimes the hot lava cooled fast. It became solid stone before the gases had a chance to seep up and escape into the air. The molten rock became solid with bubbles of gas still trapped within it. When this happened, we got rock like frozen foam, pumice stone riddled with frothy bubbles.