Iron-oxides are usually formed by precipitation from iron-enriched groundwater. Iron-oxide pigments consist of ferrous or ferric oxides, and impurities such as clay and/or manganese. Natural iron-oxide pigments have been used for centuries as coloring agents. Iron-oxide pigments are valued because they are nontoxic, weather resistant and they do not bleed or fade. The pigments are extracted from a range of ores including hematite, goethite, limonite, siderite, and magnetite. Hematite produces red pigments, limonite and goethite produce yellow and brown pigments, siderite produces brown and red pigments, and magnetite yields black pigments.
Virginia is one of four states actively producing natural iron-oxide pigments. In 2003, approximately 519 tons of natural iron-oxide were reportedly mined and produced from stockpiles in Virginia, making it the fourth largest producer in the United States (Potter, 2003). Hoover Color Corporation in Hiwassee, Pulaski County, produces ochres, umbers and siennas. Hoover Color also produces iron-oxide pigments from the Painter Mine in Wythe County. Open pit methods are used to mine these natural iron-oxides. The iron-oxides were formed by precipitation from iron-enriched groundwater, near the contact of the Cambrian (543 to 490 million years ago) Erwin Formation with the overlying Cambrian Shady Dolomite. Deposits, associated with gossans formed from weathering of the Cambrian rocks, are concentrated as small bodies or pockets composed of insoluble clay and iron oxide.
Iron-oxide production in Virginia, 1986-2003.
Selected References:
Gilmer, A. K., Enomoto, C. B., Lovett, J. A., and Spears, D. B., 2005, Mineral and fossil fuel production in Virginia (1999-2003): Virginia Division of Mineral Resources Open-File Report 05-04, 77 p.
Potter, Michael J., 2003, Iron-Oxide Pigments: U.S. Geological Survey Minerals Yearbook, p. 41.1-41.3.
Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.