Dissolution and formation of quartz in soil environments: a review
Soil Science Annual
The dissolution of quartz in soils is reviewed following brief consideration of the mineral's structure and chemistry, particularly emphasizing the effects of defects and dislocations at the crystal surface. Experimental dissolution investigations, usually under hydrothermal conditions, suggest that the principal factors controlling or inhibiting quartz dissolution are pH, and the concentrations of dissolved silica, alkali and alkaline earth cations, organic acids and aluminium and iron species
... um and iron species in the external solution. The application of these factors to natural pedogenic environments is reviewed in the context of the orders of Soil Taxonomy, as revealed mainly by SEM observations of surface etching features in different horizons of the soil profi le. For soils of a non-residual, alluvial nature it is possible that quartz grains will have been through several weathering cycles, leading to diffi culties in interpretation, as both fresh and highly weathered quartz grains may occur in intimate admixture. However, where the soil is residual and directly related to the underlying parent rock, then it may be possible to relate the nature and extent of the dissolution features on quartz to the prevailing pedogenic regime and the principal chemical factors that have been explored experimentally. The formation of quartz in soils is controversial, although it is well-embedded in the soil science literature. In most soils, quartz dominates in the sand and silt fractions and is undoubtedly of inherited origin deriving ultimately from igneous and metamorphic rocks. Criteria that could be used to confi rm the pedogenic formation of quartz in soils include separation of perfect unetched euhedral quartz crystals with an appropriate isotope composition confi rming their low temperature origin. Experimental low temperature synthesis of quartz spans a time scale ranging from fi ve years to millions of years and a critical analysis of the literature suggests that the latter is a more realistic assessment.