Part 6

1. A pocket knife, a copper penny, a piece of window glass, a steel file, and a piece of quartz to test the hardness. If you prefer to use a group of minerals of known hardness, such as those of Mohs scale described on pages 16-17, you can either collect your own or buy a prepared set from a mineral supply house.

2. A streak plate to test the color of the mineral’s streak. Mineral streak plates can be purchased, or a piece of unglazed tile can be used.

3. A magnifying glass to examine small cleavage surfaces, crystals, and rock grains. A number of different kinds can be bought, from the simple reading glass to the precisely made hand lens. A lens with ten-power magnification is good for general use.

4. A small magnet to test whether or not a mineral is magnetic.

5. Dilute (10%) hydrochloric acid (HCl), also known as muriatic acid, to test carbonate rocks and minerals. You can buy a small bottle at a drug store. Be extremely careful in handling this acid, and keep it away from small children—it is a POISON. If you spill any on yourself, it will burn your skin and eat holes in your clothes.

The rock and mineral identification charts on pages 24-41 will help you to make the simple identification tests in a methodical way.

It is a good idea to have some system of labeling your rock and mineral specimens. Some collectors carry note paper with them on field trips. Then they can write down the location and, if possible, the name of the rock or mineral. This information is either wrapped with the specimen or stuck to it with tape. One way to label large collections is to put a small spot of paint or fingernail polish on each of the rock and mineral specimens. When the paint has dried, a number can be written on it in black India ink. Then, on a file card, the name and the number of the specimen can be written, together with the place where it was found, the date of collection, and the name of the collector.

ROCK AND MINERAL IDENTIFICATION CHARTS

To help you identify them, various Texas rocks and minerals are listed together in the following charts according to properties that they have in common. Although useful, the identification charts may not always give you perfect results. For example, hardness, which is used as a guide, is not to be completely relied upon in the identification of rocks.

The charts on the following pages pertain only to the rocks and minerals that are described in this book. It is quite possible that you will find rocks and minerals in Texas that are not included in these charts.

If you find a rock or a mineral that you are unable to identify, you can check your local library for reference books that may aid you (several such references are noted on pages 100-101). If you need further help, possibly the science teacher at a nearby public school will be able to identify the specimen for you. Or if a college or university is located in your area (especially one that has a department of geology), you can obtain help there. In Texas, the Bureau of Economic Geology is a mineral information center. Most other states have similar geological research and public-service organizations. Other sources of information might be the gem and mineral societies that are found in a number of communities. Many of the members of these organizations are experts in the identification of rocks and minerals.

How To Use the Mineral Identification Charts

In the mineral identification charts (pp. 26-38), the minerals have been grouped, first of all, on the basis of luster: the first group includes the minerals that appear metallic and almost metallic (submetallic); the second group includes those that appear nonmetallic. Next, the minerals have been arranged within the two groups according to color.

After you have determined the luster and the color of an unknown mineral, turn to the Key to Mineral Identification Charts on page 25. It will direct you to the proper mineral chart.

Mineral Charts 1 through 5, which include the minerals of various colors with metallic and submetallic lusters, are subdivided according to the hardness of the minerals. To determine the hardness of a mineral that has one of these lusters, you can make the following tests:

1. Will the mineral readily leave a mark on paper?

2. If it will not readily leave a mark on paper, will an ordinary pocket knife scratch it?

3. Is it too hard to be scratched by an ordinary pocket knife?

Mineral Charts 6 through 15 are for the nonmetallic minerals of various colors. They, too, are subdivided according to the hardness of the minerals, as follows:

1. Can the mineral be scratched by a fingernail?

2. If it cannot be scratched by a fingernail, can it be scratched by a copper penny?

3. If it cannot be scratched by a copper penny, can it be scratched by an ordinary pocket knife?

4. If it cannot be scratched by an ordinary pocket knife, can it be scratched by a piece of quartz?

5. Is it too hard to be scratched by quartz?

When the luster, color, and hardness of a mineral have been determined, you may find that several minerals on the charts fit the description. To narrow your choice, you can then test other properties of the mineral. Notice the “remarks” column on the charts. In it, is mentioned anything that is distinctive about the mineral.

For more complete mineral identification lists and tables, you can use textbooks, such as Dana’s Manual of Mineralogy, revised by C. S. Hurlbut, Jr., or Mineralogy, by E. H. Kraus, W. F. Hunt, and L. S. Ramsdell.

Key to Mineral Identification Charts

If the mineral has a metallic or submetallic luster,