Formation and Evolution of Alteration Layers on Borosilicate and Basalt Glasses: Initial Stage

Abstract

ABSTRACTAn experimentally altered (1–14 days, deionized water, 90°C), synthetic borosilicate glass and naturally altered (104 years, fresh water, 0–100°C), basalt glass were characterized by analytical electron microscopy to evaluate the development of alteration layers. Layers formed on borosilicate glass are initially amorphous. With increasing age, nontronite, chlorite, septechlorite, and/or stilpnomelane appear to precipitate and grow within the amorphous matrix and on the surface of the layer. Crystals are enriched in Fe, Co, and Ni, and depleted in Si relative to the surrounding amorphous matrix. Alteration layers on basalt glass are texturally and mineralogically similar to layers formed on borosilicate glass, but the degree of crystallinity is less.