PIGMENTS AND FILLERS 



529 



Even though gradation of shades between ochers, 

 siennas, and umbers is complete, the natural iron 

 oxides can be conveniently classified according to 

 their colors. Table 108 lists their properties, sources, 

 and uses. 



Table 108. — Natural iron oxide pigment colors and sources 



Micaceous iron oxide, a pigment not included in 

 tables 107 or 108, is a special-purpose pigment used 

 to make anticorrosive paint and is not used for its 

 color. Austria is the principal source, and about 

 8,000 tons per year is mined from large continuous 

 deposits. An unspecified quantity is imported by 

 the United States, although this type of paint is not 

 commonly used here (Am. Paint Jour., 1970). In 

 England, some railway bridges painted in 1944 with 

 this pigment have not rusted except where scratched 

 by the inevitable graffiti (Indus. Minerals, 1971a). 



Most mining of iron oxide pigments in the United 

 States is on a small scale. The largest production 

 is from the Mather mine in Marquette County, up- 

 per Michigan, where it is a coproduct of iron min- 

 ing. About 25,000 tons of hematite, about 1 percent 

 of the annual mine production, is produced there 

 for the pigment, paint, and chemical industries. 

 Other production is from small mining operations 

 mainly in Georgia, Virginia, and Pennsylvania. The 

 deposits in these States are limonite and ocherous 

 material that has been leached from pyrite-bearing 

 sedimentary rocks and redeposited by ground water 



in fractures or in the residual soil. Deposits in 

 Georgia are in fractures and fault zones in Cam- 

 brian quartzites; and in eastern Pennsylavnia, 

 residual deposits are associated with Paleozoic lime- 

 stones and quartzites. The deposits of residual 

 limonite in Virginia are in two belts, one along the 

 west slope of the Blue Ridge Mountains and the 

 other associated with Cambrian quartzites in Pu- 

 laski County (Siegel, 1960). These deposits at one 

 time were the sites of small-scale iron-mining op- 

 erations, but now they produce only pigment. 



IRON OXIDE PIGMENT MARKET IN THE 

 UNITED STATES 



Although the demand for pigments is increasing, 

 the sale of natural iron oxides for pigments is de- 

 clining. In 1969, finished pigments in the amount of 

 142,900 short tons valued at $32.3 million were sold ; 

 in 1970, sale of 40,800 short tons of crude natural 

 pigments was $362,000. Imports of refined and syn- 

 thetic iron oxides were 33,431 short tons, close to 

 the amount of mine production in the United States 

 (Fisher, 1969). Synthetic iron oxides are taking an 

 increasingly large share of the world market. Im- 

 ports into the United States include about half syn- 

 thetic material. 



COMPETITIVE MATERIAL 



Although synthetic iron oxide pigment has re- 

 placed natural iron oxide in much of the market, 

 the use of the natural material continues steadily 

 in some areas. The synthetic material is produced 

 mainly in two ways — one, by precipitation of fer- 

 rous hydroxide from an iron salt solution; and the 

 other, by calcination of hydrated ferrous sulfate 

 (copperas). The first process uses scrap iron as a 

 raw material, and the second uses byproduct fer- 

 rous sulfate from the production of titanium dioxide 

 from ilmenite. No iron ore is used as raw material 

 by the synthetic iron oxide industry. West Germany 

 leads the world in this industry with exports alone 

 totahng 125,600 short tons in 1970 (Indus. Minerals, 

 1971a). The United States produced 70,507 short 

 tons in 1969. Not all synthetic iron oxide goes to 

 the pigment industry ; an unspecified amount is used 

 to produce ferrites which are increasingly being 

 used for their magnetic and electrical properties. 



PROSPECTING AND FIELD TESTS 



Almost any ocherous soil, vein, or deeply colored 

 red, yellow, or brown sedimentary rock is poten- 

 tially an iron oxide pigment. Most of these deposits 

 are diluted with clay and other impurities; conse- 

 quently their tinting strength is low. A simple test 

 in the field for tinting strength is to grind the ma- 



