Graphite is used in pencil lead, generator brushes, and lubricants 63 Selenite gypsum crystal from Bastrop County, Texas 64 Selenite gypsum rosettes from Nolan County, Texas 64 Fibrous gypsum from Terlingua area, Brewster County, Texas 65 Salt domes occur on the Gulf Coastal Plain 66 Specular hematite from Carrizo Mountains, Hudspeth County, Texas 67 Limestone from Travis County, Texas 68 Limestone quarry at Georgetown, Williamson County, Texas 69 Limonite ore is changed to metallic iron in a blast furnace 71 Metallic iron is made into steel in an open-hearth furnace 72 Magnetite, Llano County, Texas 73 Hollandite from Jeff Davis County, Texas 74 Precambrian metamorphic marble from Llano County, Texas 75 Mica minerals have perfect cleavage in one direction 76 Obsidian arrowheads 77 Opalized wood from Washington County, Texas 78 Quartz-feldspar pegmatite from Burnet County, Texas 79 Pyrite veins in white marble from Llano County, Texas 80 Cubic crystals of pyrite 80 Quartz crystal from Burnet County, Texas 81 Amethyst geode from the Alpine area of Brewster County, Texas 82 Milky quartz from Burnet County, Texas 82 Smoky-quartz crystals from Burnet County, Texas 83 Polished agate from Rio Grande gravels of Zapata County, Texas 83 Jasper from Uvalde County, Texas 84 Sandstone from Zavala County, Texas 86 Prospector 89 Sulfur is obtained by the Frasch process 92 Talc schist from the Allamoore area of Hudspeth County, Texas 93 Topaz crystal from Mason County, Texas 94 Black tourmaline crystals with milky quartz from Llano County, Texas 95 A Geiger counter is used to detect radioactivity 96 PREFACE This booklet has been designed to serve as a brief, simple guide that will be of help to school children, amateur collectors, and others who are just beginning to develop an interest in the rocks and minerals of Texas. It is a companion volume to _Texas Fossils_ by William H. Matthews III published as Guidebook No. 2 by the Bureau of Economic Geology. Numerous present and former staff members of The University of Texas contributed time and talents to the preparation of this book, and their help is gratefully acknowledged: Peter T. Flawn, Director of the Bureau of Economic Geology, Thomas E. Brown, John W. Dietrich, Alan Humphreys, Elbert A. King, Jr., Peter U. Rodda, and others, including the late John T. Lonsdale, made many helpful suggestions; John S. Harris and Miss Josephine Casey edited the manuscript; Cader A. Shelby prepared a number of the photographs; Bill M. Harris made the illustrative sketches under the direction of James W. Macon; and Cyril Satorsky designed the cover. Texas Rocks and Minerals An Amateur’s Guide Roselle M. Girard INTRODUCTION