Leaching and reconstruction at the surfaces of dissolving chain-silicate minerals

Abstract

THE pathways by which silicate minerals transform to solutes, clays and amorphous solids are relevant to a wide range of natural, industrial and even medical concerns. For example, weathered layers on silicate may have a high sorptive capacity, affecting nutrient and contamination retention in soils; less obviously, such layers on inhaled silicate grains might affect their interaction with lung tissue. Here we report the observation, in dissolution experiments on a range of chain-silicate minerals, of the formation of a near-surface amorphous region enriched in silicon and hydrogen, and depleted in other metals. Raman spectroscopy and ion-beam elemental analysis show that portions of the polymeric silicate anion in this region spontaneously reconstruct to form a network that contains four-member silicate rings and areas of incipient crystallization. If hydrolysable metals interact with the silicate anion during this reconstruction, clays and amorphous products may form directly. This process complements traditional dissolution-precipitation pathways of mineral diagenesis¹, as the silicon does not have to be present in solution before being incorporated into a growing secondary phase.