In Texas, beds of celestite occur in Permian rocks in Coke, Fisher, and Nolan counties and in Lower Cretaceous rocks in Brown, Comanche, and Mills counties. Celestite geodes and nodules are found in Lower Cretaceous limestone rocks in Lampasas, Travis, and Williamson counties, and in Permian rocks in Coke, Fisher, Nolan, and Taylor counties. Celestite is one of two minerals (the other mineral is _strontianite_, strontium carbonate) used as a source of strontium. Strontium compounds give a crimson-red color to a flame, so they are used in fireworks, tracer bullets, and flares. Perhaps you have seen a red flare set out on the highway at night to warn motorists that a truck has stalled. The chances are good that the flare’s red flame was due to a strontium compound. Some of the Texas celestite has been mined, but most of the strontium minerals now used in the United States are imported from England and Mexico. Cerargyrite. _See_ Silver Minerals. Chalcedony. _See_ Quartz. Chalcocite. _See_ Copper Minerals. Chalcopyrite. _See_ Copper Minerals. Chalk. _See_ Limestone. Chert (Flint). _See_ Quartz. Chrysotile. _See_ Asbestos; Serpentine. Cinnabar Cinnabar, which is mercuric sulfide, is the most common mercury mineral. It has a dark red or a bright yellowish-red color and is transparent to translucent. When rubbed across a streak plate, it leaves a dark red streak. If pure, cinnabar has a brilliant, shiny, nonmetallic luster. It is, however, commonly found mixed with impurities, such as clay, calcite, iron oxide, or bituminous material, and then it looks dull and earthy. Cinnabar is quite heavy—it has a specific gravity of 8.10. It is rather soft, and you can scratch it with a copper penny. Some prospectors use a quick chemical test to identify cinnabar. They rub a clean, shiny copper coin with a mineral sample that has been moistened with a drop or two of dilute hydrochloric acid. If the sample is cinnabar, a light silvery-gray coating appears on the coin. Cinnabar occurs as small crystals or as fine-grained or compact crystalline masses. It is found in veins that fill cracks in rocks and also occurs as crusts and coatings on rocks. It also may be widely scattered through rocks, such as limestones. Cinnabar occurs in the Terlingua area of Brewster and Presidio counties in west Texas. It has been mined there, off and on, since about 1894, and during this time, mercury worth many millions of dollars has been produced.