『Abstract
Six-year experiments of volcanic glass reacting with waters of
different chemistry (two freshwaters, seawater and brine) at 〜22℃
have produced the thorough transformation of mm-size glass chips
into quartz, with minor alunite and calcite. These results contradict
the current thinking about glass weathering and quartz formation.
The reaction from glass to quartz took place at an estimated velocity
ranging from 300-2000 times to 106 times faster than
the accepted values for quartz precipitation, depending on how
rates were assessed. The most likely process taking place is the
rapid transformation of cation-depleted glass into quartz. In
addition, alunite formed very efficiently from low-S glass (40±15
ppm). Such effective reaction in the absence of the accepted conditions
for alunite formation is attributed to the high Al and K content
combined with the generation of low pH conditions at the microscale.
Local, low-pH conditions may arise due to proton-for-Na substitution
at the earliest stage followed by liberation of the protons as
glass later corroded. The surprising results show a new pathway
of glass weathering and point towards reactions controlled by
microscale conditions producing high activities locally. Such
conditions may be common in the mineral-fluid interface with saline
waters, immobile waters or systems with low water:rock ratios.
The rapid precipitation of quartz at low temperature is relevant
to the origin of quartz and the silica budget in a variety of
sedimentary environments and prompts their reconsideration.
Keywords: alunite formation; quartz formation; volcanic glass
weathering』
1. Introduction
2. Methods
3. Results
4. Discussion
4.1. Reaction pathways
4.2. Relevance to geological environments
Acknowledgements
Appendices
Appendix A
Appendix B
Appendix C
References