Gail Watters, age 12, of Oak Park, 11, for her question:

What is marble made of?

Waxy marble is made from more or less the same basic materials as limestone and crumbly white chalk. All these rocky deposits are made from the shells and crusty remains of tiny creatures that lived ages ago in the ancient shallow seas of the world. Through the ages, piles of this chalky debris sifted down through the water and massed in thick layers. The seawater later receded or the sea floor was uplifted, and the limy deposits became dry land. In time they formed layers of limestone and chalk.

In some cases these sedimentary rocks became changed by heat and pressure. Their limy chemicals were remade into crystals which became metamorphic or changed rocks. Marble is a metamorphic rock remade from limy chalks, but it is made from the same basic ingredients as chalk and limestone.