Original paper

Keatite. II-Hydrothermal synthesis from silica-glass

Martin, Brigitte

European Journal of Mineralogy Volume 7 Number 6 (1995), p. 1389 - 1398

16 references

published: Dec 27, 1995
manuscript accepted: Jun 22, 1995
manuscript received: Oct 5, 1994

DOI: 10.1127/ejm/7/6/1389

BibTeX file

ArtNo. ESP147050706012, Price: 29.00 €

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Abstract The metastable, microcrystalline silica phase keatite KLS has been synthesized from solid silica-glass rods and from granular high-purity silica-glass (99.99 wt.% SiO2. Heraeus-Heralux, grain size 0.3-1.5 mm) at 400°C, 350 bars with a run time of 1-2 days in 0.01 n NaOH/H2O solutions. Analogous to the synthesis of keatite from silica-glass rods (Martin & Roller, 1990), crystallisation from granular high-purity silica takes place by nucleation and growth at very narrowly defined and critical concentrations of sodium ions in solution. Variations in sodium concentration of the solution lead to the growth sequence quartz-fibrous keatite (fibre axis [1-10]) - disordered cristobalite CD. Keatite coexists with either quartz or cristobalite - or both together - with sharp microstructural boundaries. Due to incorporation of Na+ in keatite, the solution becomes poorer in sodium, the pH value changes from 12 to 9. In this less alkaline solution, keatite transforms into quartz within a few hours up to 1-2 days. This may account for the small yields of pure keatite under hydrothermal conditions from both glass types. These results modify the existing data on the synthesis and formation of keatite and point out new aspects on the nature and the reaction kinetics of hydrothermally-formed keatite


keatitequartzcristobalitehydrothermal synthesis