TY  - JOUR
A1  - Schultze, Dina
A1  - Wirth, Richard
A1  - Wunder, Bernd
A1  - Loges, Anselm
A1  - Wilke, Max
A1  - Franz, Gerhard
T1  - Corundum-quartz metastability
T2  - Contributions to mineralogy and petrology
N2  - The metastable paragenesis of corundum and quartz is rare in nature but common in laboratory experiments where according to thermodynamic predictions aluminum-silicate polymorphs should form. We demonstrate here that the existence of a hydrous, silicon-bearing, nanometer-thick layer (called "HSNL") on the corundum surface can explain this metastability in experimental studies without invoking unspecific kinetic inhibition. We investigated experimentally formed corundum reaction products synthesized during hydrothermal and piston-cylinder experiments at 500-800 degrees C and 0.25-1.8 GPa and found that this HSNL formed inside and on the corundum crystals, thereby controlling the growth behavior of its host. The HSNL represents a substitution of Al with Si and H along the basal plane of corundum. Along the interface of corundum and quartz, the HSNL effectively isolates the bulk phases corundum and quartz from each other, thus apparently preventing their reaction to the stable aluminum silicate. High temperatures and prolonged experimental duration lead to recrystallization of corundum including the HSNL and to the formation of quartz + fluid inclusions inside the host crystal. This process reduces the phase boundary area between the bulk phases, thereby providing further opportunity to expand their coexistence. In addition to its small size, its transient nature makes it difficult to detect the HSNL in experiments and even more so in natural samples. Our findings emphasize the potential impact of nanometer-sized phases on geochemical reaction pathways and kinetics under metamorphic conditions in one of the most important chemical systems of the Earth's crust.
KW  - Experimental
KW  - Metastability
KW  - Corundum
KW  - Quartz
KW  - Nanolayers
KW  - Aluminium– silicates
Y1  - 2021
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/63595
SN  - 0010-7999
SN  - 1432-0967
VL  - 176
IS  - 4
PB  - Springer
CY  - Berlin ; Heidelberg
ER  -