Marc Naylor, age 10, of South Jordan, Utah, for his question:
WHAT EXACTLY IS A MINERAL?
Some people use the term ''mineral'' for an substance taken from the earth. Such substances include coal, petroleum and sand. But none of these are minerals. A number of different substances in food and water, such as calcium, iron and phosphorus, are also called minerals by many people. But mineralogists, the scientists who study minerals, do not consider any of them minerals.
Mineral is the most common solid material found on earth. All rocks found on the earth's surface contain minerals.
There are more than 2,000 kinds of minerals, but only about 100 of them are common. Most of the others are harder to find than gold.
A mineral is a substance that has the four following features:
1 A mineral is found in nature. A man made diamond is not a mineral, but a natural diamond is.
2 A mineral is made up of a substance that was never alive. This eliminates coal, petroleum and natural gas.
3 A mineral has the same chemical makeup wherever it is found. Sand is not a mineral because samples from different locations usually have different chemical makeups.
4 The atoms of a mineral are arranged in a regular pattern, and form solid units called crystals. Calcium and phosphorus found in milk are not minerals because they are dissolved in a liquid and are not crystals.
Some minerals have glasslike surfaces that sparkle with color while others look dull and feel greasy. Mineral crystals can also occur in many sizes. A giant crystal may weigh several tons while some are so small they have to be studied under a microscope.
Most minerals are made up of more than one kind of atom. Some have as many as five kinds of atoms in complicated arrangements. Some unit cells have six walls instead of four and others have slanted walls. Such differences in the shape of unit cells produce differences in the shape of mineral crystals.
Minerals were among the first substances to be used and described by man. The ancient Egyptians used minerals in weapons and jewelry more than 5,000 years ago.
By the late 1700s chemists began to develop correct ideas about the nature of chemical elements and other substances. These ideas helped scientists understand the chemical makeup of minerals, but did not remove the mystery about crystal shape and internal structure.
During the early part of the present century, with the development of the X ray, scientists have been able to provide the key to the internal structure of minerals.