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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on KAlSiO4 by Materials Project

KAlSiO4 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. K1+ is bonded in a distorted q6 geometry to nine O2- atoms. There are a spread of K–O bond distances ranging from 2.99–3.03 Å. Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four equivalent SiO4 tetrahedra. There is one shorter (1.75 Å) and three longer (1.76 Å) Al–O bond length. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four equivalent AlO4 tetrahedra. There is one shorter (1.63 Å) and three longer (1.64 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent K1+, one Al3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a linear geometry to three equivalent K1+, one Al3+, and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KAlSiO4 by Materials Project

KAlSiO4 crystallizes in the trigonal P31c space group. The structure is three-dimensional. K1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of K–O bond distances ranging from 2.98–3.03 Å. Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four equivalent SiO4 tetrahedra. There is one shorter (1.75 Å) and three longer (1.76 Å) Al–O bond length. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four equivalent AlO4 tetrahedra. There is one shorter (1.63 Å) and three longer (1.64 Å) Si–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to three equivalent K1+, one Al3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent K1+, one Al3+, and one Si4+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Influence of CO2 on melting of model granulite facies assemblages - A model for the genesis of charnockites

It is shown that partial melting studies at crustal pressures in SiO2-rich portions of the system KAlSiO4-Mg2SiO2-H2O-CO2 can be used in modeling the anatectic origin of charnockites. The univariant reaction phlogopite + sanidine + quartz + vapor = enstatite + liquid yields an SiO2-rich melt (granite analog) at 3 kbar; the vapor composition at the solidus is buffered to high H2O contents by virtue of the coexistence of phlogopite with its breakdown products. With higher pressures (8 and 15 kbar), the fluid phase is buffered to higher CO2 contents and the melt composition becomes enriched in K2O and MgO (charnockite analog). Melting relations are controlled through the expansion of the quartz liquidus field relative to the enstatite and sanidine fields with increasing pressure. It is noted that partial melts generated at the base of the crust in the presence of CO2-rich fluid will be of an alkaline nature and will crystallize enstatite at lower pressures. CO2-saturated melting of similar SiO2-rich bulk compositions (phlogopite-absent) through the reaction enstatite + sanidine + quartz + CO2 - liquid occurs at temperatures above 1000 C to about 15 kbar.

Wendlandt, R. F.↗