early furnaces during the colonial era utilized bog iron and small deposits or iron ore east of the mountains, until richer deposits were located west of the Blue Ridge
Source: Atlas of the Historical Geography of the United States, Distribution and Production of Iron Ore (Plate 6b, digitized by University of Richmond)
Iron is created in stars through fusion. When lighter elements (i.e., elements with fewer protons) fuse in the core of a star, they emit energy until forming iron. Furthur fusion starting with iron requires rather than releases energy, halting the process. Smaller stars then cool to become white dwarfs, then black dwarfs that drift through the universe. The iron in such stars remains in the core, unless a collision with another body releases it.
Stars with more than 25 solar masses spew their iron outward in a massive explosion. The conversion of silicon atoms into iron occurs within about one day, after which there is no more heat released from fusion:1
When the earth coalesced 4.6 billion years ago, the heavy iron concentrated in the core. It stayed molten from the heat of compression and radioactive decay until 1-1.5 billion years ago, when the inner core crystallized and the iron (and about 4-8% nickel) "froze." The outer core or iron, nickel, and a few lighter elements has remained molten. The outer core next to the inner core is hotter than that portion at the core–mantle boundary. That temperature differential creates currents in the outer core, and the flow of molten iron creates the earth's magnetic field.2
One-third of the earth is iron, measured by weight. Other major elements are oxygen (31%), silicon (19%), magnesium (13%), nickel (1.9%), calcium (0.9%), and aluminum (0.9%). All remaining elements compose 0.3% of the earth. The iron is not evenly distributed; it is just 5% of the crust by weight. The crust is primarily oxygen (47%) and silicon (28%).
In the early days of Earth, iron was dissolved in the oceans. When cyanobacteria began to photosynthesize and the percentage of oxygen in the atmosphere increased, the iron oxidized and sank to the bottom of the ocean to form banded iron formations. Those formations are some of the most valuable mining sites for iron ore today, but no more banded iron formations will be created. There is too much oxygen in the atmosphere for "reduced" iron to accumulate and then precipitate in bands again.
Gas exchange between today's oxygen-rich atmosphere and the oceans quickly triggers precipitation of dissolved iron molecules as an oxide. Oceans have such low iron concentrations now that one proposal for removing carbon from the atmosphere is to dump iron particles into the middle of the ocean. The lack of dissolved iron in the middle of the oceans, away from continental edges where rivers constantly bring minerals eroded from the crust, is a limiting factor for algae to grow. Adding iron would create a spike of algae growth that would capture carbon dioxide, then carry it to the bottom to be incorporated into limestone, silicates, and other minerals which sequester carbon in sediments.3
Much of the iron deposited in Virginia's bedrock was formed by erosion at the end of the Taconic Orogeny. Mountains were lifted up during the collision of a chunk of continental crust with the edge of Virginia. The mountains eroded away during the Ordovician Period over 400 million years ago. By the time the mountains had been reduced to almost a flat peneplain, sediments were primarily quartz (SiO2). Hard-to-dissolve quartz was distributed from the last high spots, creating the sandstone formation known in different places as Tuscarora, Clinch, or Massanutten sandstone.
In a process not yet understood well, more material then eroded in the early Silurian Period and were deposited on top of the sandstone. In scattered patches, additional sediments settled on top of the Tuscarora/Clinch/Massanutten formation. The resulting Clinton/Cayugan series of sedimentary formations is unusually rich in iron, presumably due to the source rocks in a former volcanic island arc.
Rivers have carried iron from Silurian sandstones and from later island arc terranes that accreted onto Virginia. Clay particles across the state are stained red with hematite (oxidized iron), creating the red color of bricks from Chincoteague to Cumberland Gap. There are limonite deposits in the Valley and Ridge physiographic province. Magnetite deposits were mined near the Blue Ridge from Lynchburg to Grayson County in southwestern Virginia.4
The Native Americans in Virginia used the ore as a pigment, but did not develop the technology to smelt iron. The European colonists who arrived in the 1600's were well aware of the potential to develop an iron industry in the English colonies.
During the Seventeenth Century, England's domestic iron industry was not sufficient to meet its needs, so England imported much iron from Sweden. At the start of the 18th Century, Sweden's neighbors joined forces in the Great Northern War. That destroyed Sweden's control over the Baltic, simultaneously ending Sweden's capacity to meet demand for iron throughout Europe.
England, which had relied upon Sweden for over 80% of its imports, needed a new source.5
The Chesapeake colonies became the replacement for Sweden. The Virginia Company hoped to produce iron in Virginia, after John Smith shipped several barrels of high-quality ore from Virginia in 1608. In 1619, the company shipped 150 workers with expertise in manufacturing iron to Virginia, and another 20 ironworkers were sent in 1621.
In that year an iron furnace was constructed at Falling Creek, using funds intended for the new college at Henricus. Investing the funds in the manufacture of pig iron was expected to generate a steady set of profits. However, in the 1622 uprising led by Opechancanough nearly all of the colonists at Falling Creek were killed; the furnace never operated again. The colony depended upon European imports for a century, before an iron production infrastructure was built almost from scratch.6
The lowest-cost process to produce iron was to build a small scale bloomery. Charcoal-fueled fires similar to what were used by blacksmiths smelted iron ore, including easy-to-extract bog iron.
Bloomeries could produce small batches of iron. "Blooms" of iron ore could be used to produce small amounts of iron.
Blooms were hammered and reworked to oxidize the carbon. The chemistry and physical character of a iron in a bloom was modified as ore was heated to create a "worked" (wrought) mixture of iron, a low percentage (0.1%) of carbon, and 2-4% of silicates. The silicates in the ore, with sulfur, phosphorous, and aluminum oxides, melt and bond together with the iron in the fire.
In contrast to the wrought iron produced in low-cost bloomeries, iron furnaces built in the 1700's were capital-intensive manufacturing facilities that produced cast iron products. Cast iron, when cooled, was an iron-carbon alloy with 2-4% carbon.
Molten iron straight from a furnace was cooled in molds on sand floors, in a pattern which resembled piglets suckling milk from their mother sow. Cylinders of pig iron could be transported easily to a foundry. There the iron cylinders could be remelted and poured ("cast") into new sand molds to create stove parts, firebacks (which reflected heat and made fireplaces more efficient), and other manufactured items.
Both the chemical percentages and the physical alignment of iron particles is different between cast iron and wrought iron. When cooled, wrought iron becomes a fibrous product. It is more malleable than cast iron, in which iron molecules solidify into a flake-like pattern.
Cast iron was cheaper to produce because it did not require the labor of hammering to reduce the percentage of carbon, but cast iron was also more brittle than wrought iron. Wrought iron was shaped to create tools, hinges, rims for wheels, and other products which Virginia colonists needed before the next ship arrived from England with manufactured goods for sale.7
Iron ore is present in different forms in Virginia, with iron and oxygen atoms aligning together in different ways. When iron-rich minerals weather, a yellow form called limonite remains. Much of the initial iron mining west of the Blue Ridge involve limnite deposits.
The first limonite mining was around 1760; the ore was processed in a bloomery near the Shenandoah River. Like all colonial-era iron production, the bloomery was fueled by charcoal.
There are limonite deposits in Pulaski and Smyth counties. In the shallow residual "mountain ore" deposits there, iron was originally combined with sulfur to form pyrite. In groundwater, the sulfur went into solution; the iron remained with the clay minerals.
Other limonite deposits in the Oriskany sandstone and Helderberg limestone are located in the Shenandoah Valley and near Clifton Forge. The limonite was originally in Devonian shales, deposited on top of the limestone. Iron dissolved in groundwater and was transported down to the Helderberg, where it came out of solution and created concentrations of ore. A geological report notes:8
Wrought iron could be welded together by using a flux or limestone or borax to prevent the edges of metal pieces from oxidizing during the welding process.
Throughput the 1600's, Virginia had bloomeries but lacked full scale iron furnaces. Starting in the 1700's, furnaces were built to create pig iron. That pig iron had to be heated and hammered in forges to reduce the carbon and create wrought iron, which was the basic material for manufacturing products until the development of steel.
Steel includes a higher percentage of carbon than wrought iron to create an iron-carbon alloy (with small grains, rather than a mixture or iron and iron silicates aligned as fibers), was not manufactured in significant quantities in North America until after the Civil War. Development of the blast furnace, using of coke for both heat and as a carbon source, facilitated the creation of modern steel.
Ductile iron, developed in the 1940's, is an iron-carbon alloy with more carbon that steel plus a "nodulizer" ingredient such as magnesium. Ductile iron can be bent or pulled more than cast iron. The addition of a nodulizer causes carbon atoms to form spheroidal nodules rather than the flat flakes in cast iron. The flat flakes create zones of weakness where a metal item is likely to break. Municipal and private utility companies are replacing cast iron water pipes, mostly installed before the 1960s, with ductile iron pipes to minimize waterline breaks and increase system reliability.
The construction of iron furnaces in the 1700's reflect the transfer of capital and expertise across the Atlantic Ocean. Iron furnaces mark the beginnings of an industrial base in North America:9
According to mercantile theory, the English colonists in North America were supposed to supply raw products to the mother country - not to compete with industries in England or take jobs away from workers in the British Isles.
Thomas Jefferson described Virginia's iron resources as follows:10
John Tayloe II ran the Neabsco ironworks and, after 1755, the Occoquan ironworks in partnership with Presley Thornton. In 1755, they bought 1,800 acres in Prince William County to supply fuel (charcoal) for the Occoquan furnace, and hired John Ballendine to build it. The furnace was in blast in 1756, but the partnership with John Ballendine ended in 1763.11
by 1756, the one-year old partnership at Occoquan between John Ballendine and John Tayloe II/Presley Thornton had broken down...
Source: Maryland State Archives, Maryland Gazette (November 25, 1756)
The Neabsco and Occoquan ironworks were supplied with iron from Maryland mines. They relied upon the waterpower from the Occoquan River and Neabsco Creek, charcoal from 20,000 acres of Prince William County forests owned by John Tayloe II, and oyster shells from Freestone Point used as the "flux" to lower the temperature in the furnace at which iron would separate out from the ore.12
in 1766, John Tayloe II and Presley Thornton advertised that John Ballendine had no legal right to sell any claim to the Occoquan complex to John Semple or James Douglass
Source: Colonial Williamsburg, The Virginia Gazette (Purdie and Dixon, June 13, 1766)
indentured servants, convict servants, and slaves fled from the Occoquan and Neabsco ironworks
Source: Maryland State Archives, Maryland Gazette (September 16, 1762)
Billy, a ship carpenter, ran away from Occoquan in 1765 with fellow slaves and a convict servant
Source: Maryland State Archives, Maryland Gazette (April 4, 1765)
Billie ran away again in 1768
Source: Colonial Williamsburg, The Virginia Gazette (Rind, February 09, 1769)
slaves, convict servants, and indentured servants fled from the Neabsco ironworks by crossing the Potomac River to Maryland, hoping to get a job on a ship leading away from Virginia
Source: Colonial Williamsburg, The Virginia Gazette (Purdie and Dixon, August 29, 1766)
one runaway from Neabsco Ironworks may have sought employment at Zane's Ironworks in Frederick County
Source: Colonial Williamsburg, The Virginia Gazette (Purdie and Dixon, July 8, 1773)
one runaway from Neabsco Ironworks may have fled to Gwynn's Island
Source: Colonial Williamsburg, The Virginia Gazette (Purdie, July 12, 1776)
iron ore extraction was done by hand, even after the Civil War
Source: "The Chesapeake & Ohio Railway Directory, Containing an Illustrated History and Description of the Road," View of Iron Ore Mines, Ferrol Furnace, VA. (p.302)
iron ore in Louisa County was mined along with pyrite in gossan deposits
Source: Virginia Department of Mines, Minerals and Energy, Iron in Virginia (Plate 5)
iron resources in the Shenandoah Valley were scarce in the limestone formations within the middle of the valley
Source: New York Public Library, Map of the Shenandoah Valley: showing the location of the Shenandoah Valley Railroad and of the iron-ore belts and other mineral deposits (by Jedediah Hotchkiss, 1880)
the Valley Railroad and the Shenandoah Valley Railroad both planned to gain freight traffic from iron deposits (red dashes) in Massanutten Mountain
Source: New York Public Library, Map of the Shenandoah Valley: showing the location of the Shenandoah Valley Railroad and of the iron-ore belts and other mineral deposits (by Jedediah Hotchkiss, 1880)
principal iron ore producing localities in 1919
Source: Census Bureau, Statistical Atlas of the United States, 1920 (Mines and Quarries, Plate 357)
in 1856, the Tredegar Foundry produced locomotives for Virginia railroads
Source: The Richmond Directory, and Business Advertiser, for 1856 (p.124)
the Big Hill deposit in Botetourt County was brown hematite
Source: Library of Congress, Topographical map showing the location of Big Hill iron lands, Botetourt Co., VA