Glasses secondary minerals

The following example concerns a basaltic glass altered experimentally in seawater at temperatures between 25 and 90 °C for durations ranging from a few minutes to 30 days (Crovisier et al. 1982 Thomassin Touray 1982). Regardless of the temperature, the first secondary mineral observed was a hydroxycarbonate from... 

Because the composition of the clay was independent of glass substrate composition, Zevenbergen et al. (1994) proposed that local hydrochemical conditions (rather than ash composition) was the primary control on secondary mineral formation. This conclusion suggests that at least some weathering behaviours of CCB and MSWI wastes are analogous. 

From a theoretical point of view, the gel layer is a barrier that reduces further hydrolysis of the silicate network, and is supposed to be more stable than the glass matrix, thus reducing the overall rate of corrosion. However, gel exfoliation may momentarily re-activate corrosion, at least locally. No clear trend was observed for the presence of the crystalline secondary phases identified at the surface of the corroded HT samples. The most abundant minerals are aluminosilicates, calcium phosphates, Fe- and Mg-rich minerals, and zeolites their role in the scavenging or release of metals remains ambiguous, although many mineral phases identified bear traces of metals. 

Abrajano, T. A., Bates, J. K., Woodland, A. B., Bradley, J. P. Bourcier, W. L. 1990. Secondary phase formation during nuclear waste-glass dissolution. Clays and Clay Minerals, 38,537-548. 

Cornacya Seamount. This seamount recently was discovered, named and studied by Mascle et al. (2001). It is an about 12 Ma old volcano located SE of the southern Sardinian coast. Samples from Cornacya consist of strongly altered lavas that contain enclaves of mica-rich lamprophyres. The lavas have varied porphyritic textures with ubiquitous phenocrysts of zoned plagioclase and biotite plus some amphibole and clinopyroxene that are surrounded by a glass-rich matrix containing minor Na-rich plagioclase, anorthoclase, biotite and secondary products. Accessory minerals include Fe-Ti oxides, apatite and zircon. The lamprophyric enclaves are por-... 

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