Lets Collect Rocks and Shells | Page 5

then slowly hardens into a vein.
2. NONMETALLIC MINERALS. These are of great importance to certain industries. You will find them in insulation and filters. They are used extensively in the ceramic and chemical industries. They include sulfur, graphite (the "lead" in pencils), gypsum, halite (rock salt), borax, talc, asbestos and quartz. Undoubtedly, you'll have some nonmetallic minerals in your collection. Rocks containing asbestos are especially handsome and varied.
3. ROCK-FORMING MINERALS. These are the building materials of the earth. They make mountains and valleys. They furnish the ingredients of soil and the salt of the sea. They are largely silicates--that is, they contain silicon and oxygen. (Silicon is a nonmetallic element, always found in combination with something else. It is second only to oxygen as the chief elementary constituent of the earth's crust.)
Other rock-forming minerals are the large family of micas, with names like muscovite and phlogopite. There are the feldspars, including albite and orthoclase. Others are amphiboles, pyroxenes, zeolites, garnets and many others you may never find or hear about unless you become a true mineralogist.
A rock may be made almost entirely of one mineral or of more than one mineral. Rocks containing different combinations of the same minerals are different. Even two things made of the same single mineral can be quite different. Carbon may turn up as a lump of coal or a diamond.
How Minerals Got Their Names
Names of most minerals end in "ite"--apatite, calcite, dolomite, fluorite. But many do not: amphibole, copper (the most common pure metal in rocks), feldspar, galena, gypsum, hornblende, mica, quartz.
Many minerals take their names from a Greek word referring to some outstanding property of the mineral. For example, hematite, an oxide of iron, was named about 325 B.C. from the Greek HAIMA, or blood, because of the color of its powder.
Some minerals are named for the locality in which they were first discovered. Coloradoite was first found in Colorado. Benitoite turned up in San Benito County, California. And so with labradorite and brazilite.
Other minerals got their names from famous people. Willemite was named in honor of Willem I, King of the Netherlands. The great German poet-philosopher, Goethe, could turn up in your collection as goethite. And there's smithsonite, named for James Smithson, founder of the Smithsonian Institution.
[figure captions]
Gold, jasper, uncut diamond, quartz (violet in color), halite (Carlsbad N.M.), calcite (S. Dakota), copper, turquoise (brilliant color)
Out Of This World
Some minerals come from outer space. They're meteorites, which are rock fragments. Every day, hundreds of millions of them enter the earth's atmosphere. Most of them, however, are burned up by the heat from air friction and never reach the ground. Meteors large enough to reach the earth are called meteorites. Most minerals found in meteorites are the same as those we have on earth. But, there are some rare minerals known only in meteorites. Two of them are cohenite and schreibersite.

MAIN KINDS OF ROCKS

Rocks are the building blocks of the earth's crust. They may be massive, as in granite ledges, or tiny. Soil, gravel, sand and clay are rocks. THERE ARE THREE MAIN TYPES OF ROCKS.
1. IGNEOUS rocks are those formed at very high temperatures or from molten materials. They come from magmas--molten mixtures of minerals, often containing gases. They come from deep below the surface of the earth. If they cool off while below the surface, they form intrusive rocks, which may later be revealed by erosion. When magmas reach the surface red hot, they form extrusive rocks, such as volcanic rocks. Thus, granite is an igneous, intrusive rock; lava is an igneous, extrusive rock. (Notice how the type of rock tells its past history--if you know what to look for.)
2. SEDIMENTARY rocks are formed by the action of wind, water, or organisms. They cover about three quarters of the Earth's surface. Most are laid down--as sediments--on the bottom of rivers, lakes and seas. Many have been moved by water, wind, waves, currents, ice or gravity. The most common sedimentary rocks are sandstones, limestones, conglomerates and shales. Oil is found in sedimentary formations.
3. METAMORPHIC rocks are those that have been changed from what they were at first into something else--by heat, pressure, or chemical action. All kinds of rocks can be changed. The result is a new crystalline structure, the formation of new minerals, or a change in the rock's texture. Slate was once shale. Marble came from limestone. Gneiss (pronounced "nice") is perhaps reworked granite.
[figure captions]
Igneous rocks are formed at high temperatures or from molten materials. They come from deep beneath the earth. They can be intrusive or extrusive--depending on where they cooled off.
Sedimentary rocks are formed by the action of wind, water, or organisms. They usually are laid down on the bottom of rivers, lakes and seas. Most of the earth's surface is covered by these rocks. Oil is found in