Scott Smith, age 11, of Tulsa, Oklahoma, for his. question:

How do minerals differ from rocks?

Bricks are bricks and houses are houses. Leaves are leaves and trees axe trees. So it goes with the minerals and the rocks, at least for most of the way. However, in a few cases a rock may be called a mineral and a reasonably pure mineral may occur in rock form. But most rocks in the earth's crust are composed of assorted chemicals called minerals. An amateur rockhound may refer to any sample as either a rock or a mineral. A real pro knows which is which.

The solid globe and the fluid seas are composed of inorganic chemicals called minerals. Altogether, the earth contains about 2,000 different minerals, though only about 100 of them are here in large amounts. Most of them are chemical compounds made from molecules    and all the earth's compounds are built from fewer than 100 atomic elements. Most of our familiar minerals are found in rocks    though water is classed among the most common minerals.

A sample of ordinary granite is classed as a rock because it is built from a little of this and a little of that. Its plum pudding texture is a mixture of assorted small chunks of various minerals. It may contain raisin or blueberry type nodules of the minerals hornblende or feldspar. Gritty grains of hard silica are mixed in the recipe and perhaps a few flakes of glassy mica that sparkle like diamonds when sunbeams strike at just the right angle.

There are about 100 different types of rock and granite is one of the best examples. It is found everywhere    as pebbles and boulders, in massive hulks uplifted to build mountains and in massive layers underlying whole continents.

It was formed when molten magma erupted from the bowels of the earth. As it cooled, the various chemicals in the molten mixture solidified at different temperatures and formed nodules of different minerals. Each batch forded from a unique mixture and though all granite is rated as rock, no two deposits are exactly alike.

This is not true of the mineral ingredients in the granite rock. Take for example the silica. It is made of molecules, each of which is a specifically constructed package of one atom of silicon and two atoms of oxygen. Silica molecules may be used in gritty sand, clear quartz crystal and dozens of other substances. All of them have similar properties because all are the same basic mineral with the same basic molecules.

Pocks are made from minerals and the majority of minerals are made from molecules. Of the 2,000 or so minerals, fewer than 100 are made not from molecules, but from atoms. These are basic chemical elements, such as pure gold and silver. All the atomic elements in the earth are rated as minerals    so are all the inorganic chemical compounds. The 100 or so rocks are mixtures of these various elements and compounds.