Common Rocks of Virginia
Virginia has experienced an extensive and complex geologic history. Each geologic event has shaped the landscape and left its fingerprint in the form of rocks. By studying these rocks, geologists can better understand how eastern North America formed. A few of the most common rocks found in Virginia are highlighted below. Many of these examples can be seen in our DGMR rock garden.
Click on each image below for a more detailed view.
Granite is a plutonic or Igneous Intrusive rock that forms by the slow cooling of trapped magma. As the magma cools, interlocking crystals of feldspar, quartz, and mica form. One example is Old Rag Granite, which forms some of the mountainous peaks of Shenandoah National Park in the Blue Ridge Province, including Old Rag Mountain.
Slate is a metamorphic rock that breaks along flat cleavage planes formed by layered mica minerals. It forms as the sedimentary rock shale (composed of sediment such as clay, silt, and mud) is heated and pressurized into metamorphic rock. Slate has been mined in Buckingham County of central Virginia for hundreds of years. Click here to read more about the Slate Industry of Virginia
Quartzite is a metamorphic rock that forms when quartz sandstone is subjected to elevated pressure and temperature during regional metamorphism. Quartzite is a hard rock that is resistant to both chemical and physical weathering. Quartzite occurs in the Blue Ridge and Piedmont provinces. Very pure quartz sandstone, called orthoquartzite, has many of the same physical properties as metamorphic quartzite, but is a sedimentary rock. Orthoquartzite occurs in the Valley and Ridge province.
Sandstone is a classic sedimentary rock that is composed of sand sized particles of rock and mineral. Sandstone is most commonly formed in river, beach, or near-shore marine environments. Quartz sandstone (mostly composed of quartz sand) and lithic sandstone (composed of many rock and mineral types) are most common in the Valley and Ridge and Appalachian Plateaus provinces. Arkosic sandstone (mostly composed of quartz and feldspar) occurs in the Mesozoic Basins sub-province of the Piedmont.
Coal is an organic sedimentary rock that is composed primarily of fossilized plant matter. Coal in Virginia occurs as layers in sedimentary rocks in the Appalachian Plateaus and Valley and Ridge provinces, and Mesozoic Basin sub-province of the Piedmont. Coal was formed in river, flood plain, and delta environments that existed in Virginia during the late Paleozoic and Mesozoic eras. Virginia coal is a fossil fuel resource that is used primarily to generate electricity and make steel. For more information about coal click here.
Unakite is a metamorphic rock that is formed when granite or similar rock is exposed to elevated temperatures and hydrothermal fluids during the emplacement of a volcanic dike or overlying lava flow. The resulting rock contains epidote, orthoclase feldspar, and quartz, and it is green and pink in color. Unakite only occurs in the Blue Ridge Province, and is prized as a semi-precious gemstone. Because it is relatively resistant to weathering, unakite can sometimes be found as rounded cobbles in rivers that flow from the Blue Ridge Mountains.
Gneiss is a metamorphic rock that is formed when igneous, sedimentary, and low-grade metamorphic rock is subjected to relatively high temperatures and pressures during regional metamorphism. These conditions often result in the segregation of minerals into light- and dark-colored bands. The composition, texture, and color of gneiss are variable, due to differences in the original rock type and metamorphic conditions. Gneiss is found in the Piedmont and Blue Ridge Provinces.
Conglomerate is a clastic sedimentary rock that contains abundant pebbles and cobbles. These fragments are commonly sub-round to round in shape due to physical weathering. Conglomerate is most commonly formed in river environments. The composition, texture, and color of conglomerate are variable due to differences in the source material and depositional environment. Conglomerate can be found in the Appalachian Plateaus and Valley and Ridge provinces, and the Mesozoic Basins sub-province of the Piedmont.
Schist is a metamorphic rock that is commonly formed when sedimentary, volcanic igneous, or low-grade metamorphic rock is subjected to moderately high temperatures and pressures during regional metamorphism. These conditions result in the aligned growth of micaceous minerals and give schist a reflective or shiny appearance. The composition, texture, and color of schist are variable, due to differences in the original rock type and metamorphic conditions. Schist is found in the Piedmont and Blue Ridge provinces.
Limestone is a chemical or organic sedimentary rock that is composed of lime mud and/or crystalline calcite, and may contain shells and skeletons of fossil marine organisms. Limestone often forms in quiet shallow marine environments. Due to the variety of marine settings in Virginia, limestone is most common in the Valley and Ridge province. Because it is relatively easily dissolved in water, limestone is a common host of caves and caverns in Virginia. Click here for more information about limestone caverns in Virginia.
Gabbro is an igneous rock that forms from magma that cools slowly deep in the earth’s crust. The texture of gabbro is similar to granite, but the composition is very different. Magma that produces gabbro is rich in iron, magnesium, and calcium, and relatively poor in silica. Common minerals in gabbro are plagioclase feldspar, pyroxene, and olivine. Gabbro occurs in the Piedmont and Blue Ride provinces. Diabase is a rock that is related to gabbro and occurs as dikes and sills in the Piedmont, Blue Ridge, Valley and Ridge provinces, and the Mesozoic Basins sub-province of the Piedmont.
Gold is a native element that occurs in Virginia as an accessory mineral in quartz veins. It can also be found at low concentrations in certain types of bedrock. Gold is very dense and resistant to chemical weathering. As a result, gold can sometimes be found near the base of sediment deposits in streams that drain areas containing in-situ gold deposits. Gold has physical properties that make it useful for electronics, jewelry, and dentistry. Click here for more information about gold.