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602 SENCIND[VER & AMNIONS <br />29 yr (Ciolkosz et al., 1983), 17 of 24 pedons had an AC and /or a B2 (Bw) hori- <br />zon described. Five of these pedons had weakly developed cambic horizons. <br />Hallberg et al. (1978) observed an accumulation of illuvial clay and silt in 100 - <br />yr -old minesoils, and Ciolkosz et al. (1985) described a few thin clay films on <br />ped faces or in pores that apparently formed in 15 or 20 yr. However, Roberts et <br />al. (1988b) found no evidence of illuviation after 4 yr, and Thomas and Jansen <br />(1985) found no evidence of clay translocation in 5- to 64 -yr -old minesoils in <br />Illinois. After 8 yr, Haering et al. (1993) observed Bw horizons in minesoils con- <br />structed from coal overburden strata consisting of siltstone but indicated that <br />these horizons did not meet the alteration requirements to be true cambic hori- <br />zons. Only A, AC and C horizons were observed in minesoils with at least 25% <br />sandstone. Strain and Evans (1994) described Bw horizons in some 20- to 40 -yr- <br />old sand- and gravel -pit soils, but the textures were too coarse to be cambic. <br />Short et al. (1986b) described cambic horizons in 26 of 100 profiles randomly <br />located on the Mall in Washington, District of Columbia, and classified them as <br />Inceptisols. The remaining 74 profiles were classified as Entisols. All of these <br />soils formed in about 6 m of miscellaneous fill material from excavations during <br />construction of federal buildings in downtown Washington that began in 1872 <br />(Short et al., 1986a). <br />Other types of subsurface horizons have been described or predicted in <br />minesoils. Sulfuric horizons have been described in extremely acidic minesoils <br />exhibiting active pyrite oxidation (McCloy & Sencindiver, 1990). Gypsum has <br />accumulated in some Texas minesoils leading to the speculation that gypsic or <br />petrogypsic horizons could eventually form (Doolittle et al., 1993). In Wisconsin <br />(McSweeney & Madison, 1988), precipitation of gypsum and iron oxides and <br />hydroxides has formed a Bm horizon in a sulfuric mine waste. Daniels et al. <br />(1992) observed the presence of thin Bh and Bw horizons in 5- to 15 -yr -old sandy <br />tailings derived from mineral sand mining in Florida. <br />Minesoil horizons increase in thickness with time. In Pennsylvania <br />(Ciolkosz et al., 1985), minesoil sola have been estimated to develop at approxi- <br />mately 1.6 cm yr'. A horizons have formed in 3 to 13 yr, the A -AC sequence has <br />formed in 6 to 20 yr, and the A -Bw sequence has formed in 12 to 28 yr. Varela et <br />al. (1993) reported soil formation of 2.4 cm yr' in lignite minesoils in Spain. On <br />constructed minesoil plots in Virginia, distinct A horizons of 5 or 6 cm thickness <br />developed on the minesoils after four growing seasons (Roberts et al., 1988a). <br />These A horizons were slightly thicker (5 -11 cm) and darker eight growing sea- <br />sons after construction (Haering et al., 1993). <br />Mineralogy of Pennsylvania minesoils (Ciolkosz et al., 1983) indicates that <br />clay minerals have not been altered in minesoils less than 30 yr old, even though <br />some of the minesoils are extremely acidic. However, higher extractable K levels <br />in surface horizons than in subsurface horizons of other minesoils may be due to <br />accelerated weathering of mica in surface horizons (Daniels & Amos, 1981; <br />Singh et al., 1982). Ammons et al. (1991) reported that after initial disturbance on <br />a pyritic disposal area spoil in northeast Mississippi, there was a striking increase <br />in pyrite oxidation, which released Fe and K as weathering products. Singh et al. <br />(1982) observed more total Fe than could be accounted for by oxidation of pyrite. <br />MINESOIL GENESIS AND CLASSIFI( <br />They suggested this additional Fe <br />biotite or siderite. <br />X. SUI <br />Sulfuricization is the proce <br />(FeS,), are oxidized, minerals are <br />new mineral phases are formed fi <br />ning, 1989; Fanning & Burch, 2( <br />the most important soil - forming p <br />materials (McCloy & Sencindi‘ <br />process are called acid sulfate so <br />produces an extremely low pH, ye <br />fate ions, and cations such as Ca: <br />mulate faster than they can be let <br />of sulfuric horizons. <br />Pennsylvania minesoils 2 to <br />to 3 dS m' (Ciolkosz et al., 1985) <br />rials exposed by the mining of Kitt <br />ues >2 dS -1 , and EC increased belo <br />oxidation may be more rapid in th <br />Electrical conductivity values in to <br />m Older minesoils (15 -35 yr old <br />values below 1 dS In - ' indicating <br />(Johnson & Skousen, 1995). Rathe <br />found in surrounding native soils, <br />sulfuricization (Ciolkosz et al., 19 <br />XI. SOD <br />Sodium migration and accun <br />ern Great Plains (Dollhopf et al., 1 <br />soils are placed over sodic spoils (< <br />become sodic over time as the sa <br />formance. Although water movem <br />faces because of clayey textures,t <br />holding capacity. Under these con <br />very low, so Na may migrate from <br />et al., 1980). Upward migration of <br />al., 1985) and may cause the tops( <br />tions of the topsoil may reach EC ; <br />Upward migration of salts is <br />(Dollhopf et al., 1985). If sodic mil <br />migration of salts will probably b <br />