Field Weathering Rates Versus Laboratory Dissolution Rates: An Update

Several previous studies have reported that the rate of weathering of silicate minerals in the field is 1 to 3 orders of magnitude slower than would be predicted by rates of dissolution of the same minerals in laboratory experiments (Paces, 1983; Velbel, 1985: Schnoor, 1990; Brantley, 1992; Swoboda-,~olberg and Drever, 1993). Proposed reasons for the discrepancy include: differences in reactivity between freshly-crushed and weathered minerals, errors in estimating the exposed surface areas of minerals in the field, and differences in solution composition, particularly degree of undersaturation, between the field and laboratory. We report here some experimental results that constrain some of these mechanisms.