We can discover much about Virginia's geologic history by studying the rocks found in the Commonwealth. Highlighted below are a few of these rocks; many examples can be found in our Rock Garden at our Charlottesville office.
Nelsonite is a plutonic or igneous rock that formed by the slow cooling of magma beneath the earth’s surface over one billion years ago. Nelsonite is made primarily of the minerals ilmenite and apatite. It was economically important to Nelson County in the 20th century as it was mined for titanium dioxide. A former Virginia state geologist named Thomas L. Watson first discovered this mineral in Nelson County, Virginia. Nelsonite was designated the official state rock of Virginia in 2016.
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 equivalent of shale. The clevage in slate formed when the argillaceous (clayey) rock shale is subjected to heat & pressure during mountain building. 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 sedimentary rock that is composed of sand-sized particles of rocks and minerals. 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 basins 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.
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 forms 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.
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.
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 Ridge 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.
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.