Texas is a huge state with incredibly diverse geographical features, from sandy beaches and lush hill country to hot, scrubby desert. Near the center of the state is the Llano Uplift, a giant granite dome known locally as Enchanted Rock. Texas' geologic diversity is great for mineral collectors and rockhounds looking for precious and semiprecious stones.
Texas is a great source for freshwater pearls, which are found in the Highland Lakes area of central Texas. Divers retrieve mussels from the muddy silt of Lakes LBJ and Buchanan, sometimes using a process called "brailing," which causes the mussels to open up and clamp onto a net.
The Concho River, a tributary of the Colorado River in west Texas, yields the prized pink, purple and lavender Concho pearl. Texas requires a freshwater fishing license to dive for mussels; in 2011, the cost is $30.
Blue topaz, which is extremely rare, is the official gemstone of Texas. Colorless and light-blue topaz can be found in Mason County, in the stretch of Precambrian granite west of the Llano Uplift. Due to its popularity as a locally sourced treasure, topaz is increasingly hard to find in the hill country.
Agate and jasper are two types of chalcedony, or cryptocrystalline quartz formations. Moss agate, which looks like blue cheese, as well as red and black agate, is available in Brewster County, near the western town of Alpine. Jasper, a form of chert, is usually red, green, yellow or brown and can be found in the limestone formations in the west central counties of San Saba and McCulloch, as well as in Moore County in the northern panhandle.
Cinnabar, which is the red ore from which mercury is extracted, is visible in the bluffs of west Texas. It was used by the native tribes of Texas as a form of currency and for paint. Terlingua, a small town along the southwestern border, is home to one of the largest mercury deposits in the world.
Opal is a lovely, opaque silica gemstone that can contain up to 10 percent water. Because it diffracts light, opal can take on many different colors, including white, purple, pink, blue and green. Texas opal can be found in the Catahoula Formation, a fossilized wood structure that stretches along the eastern Gulf coast of Texas and into Louisiana.