High-pressure investigation in the system SiO₂-GeO₂: Mutual solubility of Si and Ge in quartz, coesite and rutile phases

Mutual solubilities in crystalline phases in the system SiO₂-GeO₂ have been investigated up to 10 GPa pressure and 1500C temperature, using a bulk composition of 50 mol% GeO₂. Solid solution of up to 40 mol% GeO₂ into the mineral quartz has been confirmed as well as solubility of Si into GeO₂ rutile (argutite) and Ge into SiO₂ rutile (stishovite) phases and limited Ge into coesite. Solubility of Ge in quartz is very high, and decreases with pressure, with the univariant quartz-out reaction occurring near 3.4 GPa at 1200C. The solubility of GeO₂ in coesite is highest at 3.4 GPa (about 8 mol%) and decreases with increasing pressure. Significantly more extensive solubility than previously reported for the rutile phases has been found and measured in detail as a function of pressure and temperature. Extensive solubility of SiO₂ in GeO₂ is found in argutite at 1200C, increasing strongly with pressure and reaching a maximum of 25.2 mol% SiO₂ in GeO₂ at 9 GPa. At this point coesite (ss) plus argutite (ss) react to form a stishovite phase with 18 mol% GeO₂, and the mutual solubility in both phases decreases above this pressure. At 1500C, similar solubilities are observed but the maximum SiO₂ solubility in argutite of just over 25 mol% occurs near 10 GPa. All these solid solutions can be recovered to ambient temperature and pressure. Phase diagrams and unit cell information of the phases are presented here. Based on these results, a useful and industrially relevant, application for accurately measuring high pressure is suggested.