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?