Though it is not a true stone, petrified palmwood was adopted as the state rock of Texas in 1969. In the same year, blue topaz was named the state gemstone. Neither of these stones are found statewide, though both are known for their beauty and are often cut and polished to be worn as jewelry.
Petrified palmwood is the state rock of Texas as well as Louisiana. These two states share a border, and it is in this area that most of the petrified palmwood in Texas is found. In the Cretaceous period, approximately 100 million years ago, eastern Texas was a part of a large swamp, bordering on a large sea. This lush, tropical landscape was home to many palm trees, though the species of palm found in Cretaceous era Texas are now extinct.
In order to transform a palm tree into the state rock of Texas, palm trees had die and be covered by mud and clay before the living tissues in the trees rotted. Under the right conditions, the palm wood would mineralize, transforming from plant cells into the fossil, petrified palmwood. After millions of years, the wood of the palm tree was no longer wood but the compound silica, or silicon dioxide.
The state rock of Texas is about as hard as glass, though a bit more durable, and is often polished and cut to be used as jewelry or decorative pieces. Though all the original components of the living palm wood are gone, petrified palmwood looks like a slice of living wood, and the long fibers that helped keep the tree upright can still be seen in the fossil. Depending on how it is cut, these fibers can appear as dots, stripes or cones.
In addition to the state rock of Texas, there is a Texas state gemstone. Texas blue topaz, or simply blue topaz, is found near the center of the state, especially in the area around Mason County. It has a light blue color, though an artificially produced blue topaz may appear as a deep blue.
Structurally, there is no difference between blue topaz and any other color variation of this stone. It is found throughout the world and is made of aluminum, fluorine, and silicate, which combine in a predictable crystalline structure. In Texas, both blue and clear topaz can be found, though the blue is considerably rarer, with deeper blues exceedingly difficult to find.