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598 SENCINDIVER & AMMONS <br />al., 1980; Sencindiver, 1977). Many of these mottles and mixed colors are related <br />to parent material deposition (relic) or may be the result of parent material weath- <br />ering and/or chemical reactions related to the process of sulfuricization (pyrite <br />oxidation) (Fanning & Fanning, 1989; Fanning et al., 1993). Dark colors of sur- <br />face horizons normally result from recent organic matter accumulation and <br />decomposition. The presence of coal fines or high -C rock fragments produces <br />dark colors in some subsurface horizons. These materials often result in erratic <br />distribution of organic C with depth because of the backfilling and topsoiling <br />processes (Ciolkosz et al., 1985; Smith & Sobek, 1978). In situations where soils <br />are replaced, such as prime farmlands, gray colors from pre - existing soils with <br />drainage problems are possible. These replaced soils may no longer be in poorly <br />drained landscape positions so that higher chromas may develop with time. <br />VI. STRUCTURE <br />Most minesoils, even those that are 1 or 2 yr old, have weak to moderate <br />structure that has developed in their surface horizons. This structure is primarily <br />granular or subangular blocky (Ciolkosz et al., 1985; Daniels & Amos, 1981; <br />Roberts et al., 1988b; Thomas & Jansen, 1985), but sometimes it is platy (Bus - <br />sler et al., 1984; Schafer et al., 1980). The platy structure often results from <br />machinery compaction during minesoil construction. Structure developed since <br />the placement of earth materials by mining equipment also has been observed in <br />some subsurface horizons of older minesoils (Ciolkosz et al., 1985; Daniels & <br />Amos, 1981; DeMent et al., 1992; Schafer et al., 1980; Thomas & Jansen, 1985). <br />McSweeney and Jansen (1984) described a new type of structure in Illinois <br />minesoils, which they called " fritted." This structure has a similar appearance to <br />semifused spheres and consists of rounded aggregates loosely compressed <br />together. Size classes are similar to blocky. Fritted structure is formed in materi- <br />als excavated by a bucket -wheel excavator and transported on a conveyor belt. <br />Plant root systems were more extensive in the Illinois minesoils with fritted struc- <br />ture in the subsoil than in scraper constructed minesoil subsurface horizons that <br />were massive and compact. <br />VII. BULK DENSITY AND POROSITY <br />Numerous investigators have reported minesoil bulk density values to be <br />higher than contiguous native soils (Bussler et al., 1984; Dunker & Barnhisel, 1997; <br />Potter et al., 1988; Schafer et al., 1980; Smith et al., 1971; Thurman & Sencindiver, <br />1986). Some of these authors reported only total bulk density, whereas others <br />reported bulk density adjusted for rock fragments, as well as total bulk density. <br />Thurman and Sencindiver (1986) reported that adjusted bulk densities of surface <br />horizons from 25 -yr -old minesoils were higher than the native soils, but the bulk <br />densities of minesoil subsurface horizons were similar to the unmined soil. <br />In a study comparing minesoils of different ages (Schafer et al., 1980), bulk <br />density of the old minesoils ( -50 yr) was equal to or less than the native soil. New <br />41INKSOIL GENESIS AND CLASSIFI <br />nmie.oils had a slightly higher b <br />,cm ubuted the differences to minis <br />t'he old minesoil had been dump <br />new minesoils were constructed w <br />diIl'erent -aged lignite minesoils in <br />minesoils to be significantly lowe <br />1990). These bulk density differe <br />meanie inputs on older sites. <br />In a study of topsoiled and <br />.ullusted bulk density values were <br />that had been topsoiled. Equipmei <br />soul. Most studies have shown tha' <br />soil hulk density (Short et al., 198 <br />Varela et al., 1993). The lower del <br />logical activity, organic matter inc <br />cycles. <br />Compaction of minesoils n <br />plant root extension. Minesoil c <br />major limiting factor to successl <br />However, some investigators (S <br />Bested that minesoils with no ph <br />compacted layers, extremely ac <br />monly deeper than native soils d <br />soils have a greater depth for 1 <br />capacity. Texas studies (Bearden <br />dactvlon (L.) Pers.] roots extent <br />sediments of the Wilcox Group, <br />of the area. <br />VII <br />On undisturbed landscapes <br />isms, relief or topography, paren <br />factors of soil formation (Jenny, <br />and Jansen (1981) have observe( <br />does little to help perceive the sI <br />active factors of soil formation <br />mation. Parent material variabili <br />morphic models. Grube et al. (1 <br />pedologic, and chemical inform <br />of soils that form in specific roc <br />solution, leaching, oxidation, o <br />and aggregation of soil particles <br />ferentiate minesoil properties a <br />al., 1988a). <br />