the limestone deposits in Loudoun County were mined primarily for agricultural lime prior to the Civil War
Source: Library of Congress, A map of the state of Virginia, constructed in conformity to law from the late surveys authorized by the legislature and other original and authentic documents (1859)
Virginia has different types of rocks rich in calcium carbonate, including limestone, dolomite, marl, and travertine.
Virginia's tourist caves are in limestone deposited roughly one half a billion years ago. Various types of cave formations, primarily stalactites and stalagmites, evolved as calcium carbonate dissolved in groundwater has crystalized. The youngest limestone in Virginia solidified in the last second, when a drip of water evaporated at the end of a "soda straw" formation in a Virginia cave and deposited a tiny addition to that straw.
Earth's original limestone formed as the atmosphere rich in carbon dioxide and other gases was absorbed into the oceans. The dissolved gases combined with dissolved ions of calcium and magnesium, and when supersaturated limestone (calcium carbonate) and dolomite (calcium-magnesium carbonate) crystals were precipitated onto the bottom of the ocean floor. The earth's atmosphere and oceans have maintained an equilibrium that sequestered carbon in rock.
In contrast, once-similar Mars had an atmosphere with a higher percentage of sulfur. When dissolved in the oceans that once existed on Mars, the resulting sulfuric acid prevented the precipitation of limestone and dolomite. Rovers sent to Mars are finding sulfur-rich minerals in the places where water once existed, whereas earth's oceans are coated in calcium-rich minerals.1
Within what is now Virginia, the oldest limestone accumulated as much as 750 million years ago at a time when Virginia was part of the supercontinent Rodinia. During or after the failed rifting event, when volcanic eruptions and eroding sediments created the formations around Mount Rogers, the sediments were metamorphosed into marble. Local tradition holds that a block of stone from a quarry in Grayson County near Troutdale was used in the construction of Grant's Tomb.2
active and abandoned limestone quarries are located at Front Royal on the Shenandoah River
Source: ESRI, ArcGIS Online
Around 600 million years ago, carbonates accumulated in shallow freshwater lakes and/or in marine bays in what is now Loudoun County. Those sediments were gradually buried below the sands and cobbles deposited by freshwater rivers, or in saltwater embayments.3
Rodinia split up, massive basaltic lava flows erupted, and the sandy and lime-rich sediments were buried. Later tectonic forces in the Taconic, Neo-Acadian, and Alleghenian orogenies also generated heat and pressure. The sediments were compressed into rocks ("lithified") known today as the Swift Run Formation, and the beds of limestone metamorphosed into marble.
By the time Thomas Jefferson was elected president, the 50' thick layer of marble near Goose Creek in Loudoun County was being quarried. The marble was crushed, burned to produce agricultural lime, and spread on the fields of Oatlands and other plantations to enhance productivity of the soil. The Virginia Marble Company operated the quarries after the Civil War, and it became one of the largest employers of African-American men in the county.
tectonic pressures metamorphosed Precambrian deposits of limestone into marble (circled in blue) which was mined near Goose Creek between 1798-1949
Source: US Geological Survey (USGS), Geologic Map of Loudoun County, Virginia
That Loudoun County marble was used to produce the Confederate memorial erected in Little Washington, Rappahannock County and the 1898 Confederate Heroes Monument in Page County. (A second marble monument installed later in downtown Luray, and two other Confederate soldier memorials in Lunenburg and Spotsylvania counties, were sculpted in Georgia.) The Virginia Marble Company produced terrazzo (marble chips) until 1949 at Goose Creek.4
The largest Virginia deposits of limestone and dolomite are in the Valley and Ridge physiographic province. Limestone outcrops are readily visible along Interstate 81, which crosses that province from the Shenandoah Valley in the north to the Tennessee border.
nearly all limestone exposed at the surface in Virginia today was deposited in the Iapetus Ocean, before the addition of the land between the Blue Ridge and Atlantic Ocean
Source: ESRI, Ecological Tapestry of the World
Roughly 500 million years ago, the region was located at the edge of the supercontinent Rodinia. It was underwater, near the shoreline of a part of the Iapetus Ocean known as the Sauk Sea. At the time, "Virginia" was located south of the Equator, and coral reefs grew in the warm waters. Zooplankton and larger forms of life protected by shells thrived in the Sauk Sea. When they died and sank to the bottom, deposits of limestone (and magnesium-rich dolomite) gradually accumulated.
Tectonic forces moved chunks of continental crust and closed the Iapetus Ocean. Terranes from island arcs were pushed against the edge of Virginia in the Taconic, Acadian, and Alleghenian orogenies. The island arcs widened the crust over the last 400 million years to create the Piedmont and Coastal Plain physiographic provinces, but the orogenies also narrowed the old continent. The sediments on the floor of the Sauk Sea were cracked, thrust slid up ramps of softer shales, and stacked on top of other layers like pancakes.
tectonic forces during orogenies cracked sedimentary layers at weak zones and slid layers of limestone on top on one another, like a stack of pancakes
Source: US Geological Survey (USGS), Lateral Ramps in the Folded Appalachians and in Overthrust Belts Worldwide - A Fundamental Element of Thrust-Belt Architecture (Figure 4A)
A slice of the igneous bedrock, the granites and gneisses deep underneath the Sauk Sea sediments, was a slice broken off the edge of the continent. That crust was shoved 40 miles to the west, emplacing the Blue Ridge at least partially on top of the much younger limestone/dolomite layers. The Blue Ridge fault marks the western edge of the slice of igneous bedrock that was moved westward.
Carbonate layers that were once at the bottom of the Sauk Sea, on the edge of Rodinia, are now west of the Blue Ridge and far from the modern shoreline. Those limestone/dolomite sediments are the common bedrock in the Shenandoah Valley, in the Roanoke Valley, in the New River Valley, and in the valleys of the Tennessee River's upper tributaries (Holston, Clinch, and Powell rivers).
Some of large limestone quarries that excavate the limestone crush it to produce agricultural lime, but most quarries sell the stone for construction. The railroads haul limestone gravel east through the Blue Ridge to support the beds of the tracks. East of Thoroughfare Gap, railroad tracks are placed on top of distinctly-colored grey rocks that appear out of place in the iron-rich bedrock of the Culpeper Basin.
As far back as the mid-1700's, Shenandoah Valley residents used limestone blocks to build fortified houses that offered protection against Shawnee, Seneca, and Cherokee raids. The standard architecture at Virginia Tech relies upon quarries near Blacksburg that supply "Hokie Stone" from sediments deposited 500 million years ago. Courthouses and other public buildings west of the Blue Ridge are often made of limestone.
One major deposit of limestone is exposed on the surface near Leesburg, east of the Blue Ridge in Loudoun County. Limestone conglomerate at Raspberry Falls/Leesburg ("Calico marble" or "Potomac marble") is the Leesburg Member of the Balls Bluff Siltstone. The limestone cobbles in the conglomerate were deposited originally in the Sauk Sea, in sediments now exposed in Frederick County Maryland as the Frederick Limestone and Tomstown Formation. During the Triassic Period, carbonate clasts were eroded in storms, carried downstream in flooded river channels, and deposited in debris-flow deposits on alluvial fans in the Culpeper Basin.5
The "Potomac marble" is actually a conglomerate, not metamorphosed limestone. Some was quarried in Maryland and used for columns in the Capitol building in Washington, DC.
Conglomerate mined near Leesburg was processed into agricultural lime. One historic quarry is located near the modern pond in Olde Isaak Walton Park. Others are located on Lime Kiln Road, between US 15 and Snickersville Turnpike.6
Lime Kiln Road in Loudoun County reveals the geologically-based industry there
Source: US Geological Survey (USGS), Mineral Resources Data System
The only known natural caves in Virginia located east of the Blue Ridge are in the Leesburg Member, north of Leesburg. There are also sinkholes in Loudoun County east of Route 15, and the local geology is reflected in the name of the stream "Limestone Branch."
the only natural caves in Virginia east of the Blue Ridge are in the conglomerate known as the Leesburg Member (circled in red), which also produced sinkholes at Temple Hall Regional Park
Source: US Geological Survey (USGS), Geologic Map of Loudoun County, Virginia
There is also a Limestone Creek that flows into the Rivanna River in Albemarle County, five miles southeast of Monticello. Thomas Jefferson purchased in 1771 and 1773 four acres of "limestone land" (Everona Formation) for production of mortar, which was needed to build his mansion house. The lime-based mortar was used between the bricks to cement them into weight-bearing walls, and to coat the columns on the West Front that appear on the nickel coin.
Lime produced from the Everona Member of the True Blue Formation was also used to build the University of Virginia. The layer of limestone is 1,000' thick at Limestone Creek, in the trough of the Everona Syncline.7
Jefferson bought a quarry on Limestone Creek, to obtaine lime from the Everona Member for building Monticello
Source: US Geological Survey (USGS), The National Map
Orange County has identified the Everona Limestone as "one of the County鈥檚 greatest groundwater assets," and mapped it as part of the Groundwater Protection Zone.8
the Orange County Comprehensive Plan identifies the Everona Limestone, in the trough between two slices of the Blue Ridge, as a potential source of groundwater
Source: Orange County, 2013 Comprehensive Plan (p.81)
Limestone in Virginia is crushed for both agricultural use as a fertilizer, and for a variety of industrial uses. Underground coal mines spray a slurry with limestone on their walls, to reduce methane emissions which could become explosive. The decline in underground coal mining, as natural gas became less expensive after fracking increased supply, led to a layoff at the Carmeuse Lime and Stone quarry outside of Strasburg. The quarry was located far from the coal mines, but had developed a successful business selling "rock dust" to increase safety underground. As coal-fired power plants closed, demand for the limestone powder declined along with the demand for coal.9
In 2019 the Clorox Company, which sold Fresh Step cat litter, wanted to build a manufacturing facility next to the Carmeuse quarry in Strasburg. Frederick County was an attractive site for the business because of local labor availability and wages, and the particular site was preferred because limestone is a key ingredient in cat litter. A conveyor belt was planned to transport the raw limestone excavated from the quarry to the plant, and the final product would be transported via the adjacent Norfolk Southern railroad.
Frederick County supervisors rejected a rezoning proposal on 146 acres that was needed for construction of the cat litter plant, despite the potential addition of 100 jobs and $500,000 annually in tax revenue. Residents on Brucetown Road objected to the anticipated truck traffic on a road with already was rated with a Level of Service of "F" by the Virginia Department of Transportation. The Clear Brook quarry had at least a 15-year supply of limestone, but supervisors were concerned that eventually the limestone might be trucked via Brucetown Road to the cat litter plant.10
the Clorox cat litter plant would have been located on 146 acres (red polygon) near the Carmeuse quarry in Frederick County
Source: ESRI, ArcGIS Online
in the Cambrian Period, the limestones of the Valley and Ridge physiographic province were deposited in a shallow Iapetus Ocean
Source: Dr. Ron Blakey, Paleogeography and Geologic History of North America