Lets Collect Rocks and Shells | Page 7

have colored pictures that help.
But identification is best made by noting the physical characteristics of the rock or mineral. For minerals, there's a hardness scale in which a mineral of the higher number can scratch a mineral of the lower number but not be scratched by it. The scale is: 1) talc; 2)gypsum; 3) calcite; 4) fluorite; 5) apatite; 6) orthoclase; 7) quartz; 8) topaz; 9) corundum; 10) diamond. Remember it by this silly sentence: "The girls can flirt and other queer things can do."
When on a trip, remember that a fingernail has a hardness of 2.5; a penny, 3; a knife blade, 5.5; and a steel file, 6.5. Use these to scratch your sample and you can get an approximate idea of its hardness.
You can buy a set of hardness points. They're pointed pieces of minerals set in brass tubes, each marked with its hardness scale. The set costs about $30 (half that if you assemble your own).
Other tests for identifying minerals include specific gravity (weight of mineral compared to the weight of an equal volume of water), optical properties and crystal form, color and luster. Minerals differ in cleavage and fracture (how they come apart when cut). They leave distinctive streaks on unglazed porcelain. Some are magnetic, some have electrical properties, some glow under ultraviolet or black light, some are radioactive, some fuse under a low flame while others are unaffected. Many studies with the dissolved mineral can identify it beyond doubt.
But most of these are too complicated for the beginner. As you read, look at pictures and samples, and talk with other rockhounds or leaders of mineralogy clubs, you'll get better at identifying rocks. Museum experts and your state's geologist can help, too.
[figure captions]
Specific gravity balance
Blowpipe analysis

GEMS FOR THE LUCKY FEW

If you're lucky, you'll find gems or semiprecious stones. Gems are the finer, more crystalline forms of minerals which are ordinarily less beautiful and spectacular. The true gems are diamonds, emeralds, rubies and sapphires. All others are semiprecious and ornamental.
Diamonds are pure carbon, but did you know that rubies and sapphires are corundum minerals--rare forms of alumina. In slightly different form, they'd turn up on emery paper.
Other stones you might find are the quartz gems: rose quartz, amethyst, rock crystal, agate, jasper, bloodstone. Or opaque gems such as jade, moonstone, lapis-lazuli, obsidian, and turquoise.
You don't have to find them. You can buy gems in the rough or in blanks, then cut and polish them to make your own jewelry or decorations. This takes practice, plus a cutting and polishing outfit, wood vise, maybe a diamond wheel. (Or you can join a lapidary club that might already have the equipment).
First learn to make cabochons--stones with round or curved surfaces. Then try cutting facets (or faces) in transparent gems. Learn by reading, working with an expert, trial and error. Making jewelry is fun, and collecting gems is as interesting as collecting rocks and minerals; it brings the world into your home. From the West come agates, jaspers, petrified woods; from the East, colorful marbles, serpentines, granites. Alaska, Idaho, Connecticut or Austria will yield dark red garnets. Fine moonstones come from Ontario; quartz crystals from Hot Springs, Arkansas, can be compared with similar ones from the Swiss Alps or Brazil.
Rock collecting is a hobby you can tailor to your taste. But whether you concentrate on an area close to home or travel across whole continents, you'll find that the pleasure and knowledge you gain from your collection are matched by the fun and adventure of the search.
[figure captions]
Drop sticks to hold stones
Diamond cutting wheel

[BACK COVER]

A Brontosaurus
Shell Oil Company
Revised 8/88

End of Project Gutenberg's Let's collect rocks & shells, by Shell Oil Company
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