Diane Gallano, age 14, of Fredericton, New Brunswick, Canada, for her question:

Is it true that some rocks actually grow?

Rocks, of course, are inorganic or non living minerals. They cannot multiply and grow as living things do. Nevertheless, in a sense, some rocks do grow from other rocks. Perhaps it is more correct to say that they form from other minerals. A region of swampy flats may become dry. In time its soft muds change into stiff beds of hard shale. With still more time, the shales may change into more oompact layers of hard slate. You might say that the slate grew from the original mud even though it shrank during the process as it became heavier and more dense.

People who farm rocky soils often suspect that rocks grow in the ground like crops. They removed loads of pebbles from the surface, expecting that this is the end of them. But next season, more rocky pebbles have arrived to take their places. Actually, they were there all the time, down lower in the soil. Rain and melting snows moved the plowed and loosened soil and a new crop of rocks appeared on the surface. But they did not grow as plants and living animals grow.