Locations of Rocks in Texas Dallas El Paso Guadalupe Mountains Austin Houston Igneous and Metamorphic Metamorphic and Sedimentary Sedimentary Metamorphic Igneous Color Type of rock Gulf of Mexico

Rock-forming and rock-destroying processes have been active for billions of years. Today, in the Guadalupe Mountains of western Texas, one can stand on limestone, a sedimentary rock, that was a coral reef in a tropical sea about 250 million years ago. In fact, Texas contains mostly sedimentary rocks, with east Texas underlain by a Cretaceous and younger sequence of sediments. Sedimentary rocks can be found in almost all areas of Texas, save for the High Plains, which are composed of mostly silts and fine sands, and the Gulf Coastal Plains, which feature mainly sands and mud. Several of the sedimentary rocks that are abundant in Texas are limestone, lignite, coal, and gypsum. A few exposures of Precambrian igneous and metamorphic rocks are found in the central and western parts of the state, near El Paso. The ancient volcanic (igneous) rocks were formed early in the Earth's history. A large percentage of the igneous rocks in central Texas is graphite. The metamorphic rocks that characterize northern and western Texas are largely slate, quartzite, and gneiss.

3 Major Groups of Rocks Metamorphic Igneous Sedimentary Quartz Granite Examples: slate quartzite granulite phyllite marble obsidian (volcanic glass) granite basalt andesite limestone sandstone shale quartz magnetite Forms when a pre-existing rock is transformed physically and/or chemically by extreme heat and pressure. Studying metamorphic rocks provides us with information about the temperatures and pressures that occur deep within the Earth's crust. Forms when molten rock (magma) cools and solidifies, either below earth’s surface as intrusive (plutonic) rocks or above the surface as extrusive (volcanic) rocks. Over 700 types of igneous rocks have been described, and most of them are beneath the Earth's crust. Forms as a result of earth erosion. Small pieces of earth are worn away (by wind, water, etc.). They fall into bodies of water and settle to the bottom. Earth falls upon earth and layers are formed. Slowly, the bottom layers of earth turn into rock. Sedimentary rocks cover 75% of the Earth's surface. Metamorphic Igneous Sedimentary 3 Major Groups of Rocks Quartz Granite Marble