528 



UNITED STATES MINERAL RESOURCES 



INTRODUCTION 



This report reviews the rocks, minerals, and fuels 

 consumed in the United States for the production 

 of pigments and fillers. It discusses (1) only the 

 pigments made directly from minerals, metallic ores, 

 and carbon black, made from gas and oil, and (2) 

 only rock- and mineral-based fillers. Most natural 

 mineral pigments and fillers are processed simply 

 by grinding to very fine sizes. In addition some are 

 calcined, and colored pigments are finished by mix- 

 ing with white pigments to obtain desired tints. 



Other pigments are manufactured from metallic 

 ores by chemical processes, and carbon black is pro- 

 duced from gas and oil by incomplete combustion 

 or petrochemical methods. 



TERMINOLOGY 



Fillers in the simplest sense are powders that are 

 added to substances for some useful purpose. Al- 

 though mineral fillers originally were intended to 

 act mainly as adulterants and substitutes for more 

 expensive compounds, their principal function now 

 is to give some desirable or necessary property to a 

 product. Commonly one of the many functions of 

 fillers is to add color. Therefore, the functional field 

 of fillers overlaps that of pigments, which in the 

 purest sense are insoluble powders added only to 

 color or tint. Because of the coloring function of 

 fillers, some users refer to them as pigments. For 

 example, in the rubber industry the finely divided 

 clay and carbon black acting as reinforcing agents 

 are called "rubber pigments," even though coloring 

 is not necessarily their function. A recent paper 

 (Kollonitsch and others, 1970a, b), in which the 

 market for many mineral fillers is discussed, calls 

 them "functional mineral pigments," distinct from 

 "primary pigments" whose only function is coloring. 



The paper industry, a major consumer of fillers, 

 calls them "fillers" or "coaters" depending upon 

 whether the filler is "loaded" among the fibers of 

 the paper sheet or is used as a surface coating. The 

 paint industry uses fillers to help form the paint 

 film and to extend or spread out the more expensive 

 pigments and hence calls fillers "extenders." The 

 pesticide and fertilizer industries use the inert but 

 absorbent qualities of some fillers to dilute and 

 carry the chemicals and hence call them "carriers." 

 This carrier-chemical combination in turn is diluted 

 further for field application by fillers known as 

 "diluents." 



In order to avoid confusion, mineral filler as used 

 in this report is synonymous with the special terms 

 just mentioned and is a finely ground and generally 

 inert rock or mineral powder added to give desira- 



ble or necessary physical properties to a finished 

 product. A mineral pigment as used in this report 

 is an insoluble powder added only for the purpose 

 of imparting color, tint, or opacity to a finished 

 product. By these definitions, a pigment is a one- 

 purpose filler serving only to color. 



NATURAL PIGMENTS 



A comprehensive survey of the iron oxide pigment 

 market in the United States and Great Britain re- 

 cently appeared in the periodical "Industrial Min- 

 erals" (1971a). The principal previous study of 

 mineral pigments was by Siegel (1960). Much of 

 the information in the following paragraphs is from 

 these sources. 



Mining of pigments was one of the earliest min- 

 eral industries of primitive man and in America 

 was done extensively by the Indians. Most notable 

 among the mineral pigments are the earth colors 

 produced by iron oxides. Some other mineral pig- 

 ments are ultramarine from lapis lazuli, green 

 earth from weathered basaltic tuffs, and a very un- 

 stable blue from azurite. Alteration of the latter 

 might be responsible for the now green skies in 

 some old Italian paintings (Ladoo and Myers, 1951). 



Most pigments now are produced synthetically 

 from ores or metals or as byproducts of other proc- 

 esses. The only important production of mineral 

 pigment is from the natural iron oxides because 

 they are inexpensive and available, although the 

 market for these too is threatened by synthetic iron 

 oxides because the consistency of color and particle 

 size from synthetic iron oxides are more easily 

 controlled. Increasing use of organic dyes has also 

 cut deep inroads in the natural pigment market. 



IRON OXIDE PIGMENTS 



The principal iron oxide pigments are ochers, 

 siennas, and umbers. Compositions vary widely, but 

 limonite and hematite are the principal coloring 

 agents. Mixed with these are various quantities of 

 manganese oxide, clay, and in the case of Vandyke 

 brown, organic material in the form of humates. 

 Table 107 gives the approximate composition of 

 earth pigments. 



Table 107. — Approximate composition of earth pigments, 

 in percent 



[Adapted from Siegel. 1960] 



