Minesoils from 1 to 50 years old in southeastern Montana were compared to adjacent natural soils. Due to their maninfluenced origin, minesoils had several unique morphological properties which made them difficult to classify. Weakly consolidated rock fragments, common in minesoils, acted in part like soil in supplying water and in part like rock in preventing root penetration. Low chroma mottles were common in minesoils without the influence of a high water table. Organic C content from 0–10 cm soil depth reached levels found in natural soils within 30 years, but will not reach equilibrium at 20–50 cm for 400 years or more. Litter accumulation was common under pioneer vegetation on minesoils resulting in wide C/N ratios; reduction in available N; successional stagnation; and reduced plant community production. Soluble salts were leached downward in minesoils in tens of years, but thousands of years will probably be required for carbonate removal to occur in the upper 50 cm. Soil structure developed more quickly near the soil surface (10–50 years) than below 10 cm (50–200 years), and was attained sooner in clayey than in sandy minesoils. Many characteristics of minesoils are expected to always be different from natural soils. Well‐designed minesoils can be highly productive, however, in a few cases perhaps exceeding the potential of natural soils.

Many alluvial Argids in central Nevada are cemented by illuvial silica and CaCO3. In loamy soils, microsite deposition of these authigenic components tends to be mutually exclusive, with silica being finely distributed throughout the plasma phase and calcite plugging packing voids formed by skeleton grains and root channels. The following model is proposed to explain the differences in depositional locations of silica and CaCO3. As soils dry, calcite precipitates rapidly in an ionic, diffusion‐controlled reaction while monosolicic acid, which requires greater activation energy for Si‐O bond breakage prior to precipitation, is concentrated in the solution phase. Monosilicic acid [Si(OH)4] can diffuse away from the evaporation front into smaller pores where, in contact with higher surface areas, it is absorbed onto clay, sesquioxide, and weathered primary mineral surfaces. Adsorbed silica is a template for further adsorption, and on drying, the precipitation of opaline silica (SiO2). The resulting SiO2 polymers form bonds between adjacent Si(OH)4 absorbing soil particles without necessarily plugging the voids between them. In contrast, CaCO3 plugs large voids by preferentially precipitating on previously deposited calcite crystals. Calcite is more easily redissolved than opaline silica and tends to move lower in the soil profile during wet years. Differences in precipitation processes result in silica‐rich, calcite‐poor argillic and upper duric horizons that grade to more strongly cemented duric/calcic horizons. The latter are characterized by horizontally distributed low calcite durinodes interspersed by more calcareous internodal areas.