Characterization of K-Al-, K-Fe- and K-Mg-priderite grown from melts.

Single crystals of K-priderites (Kx(M,Ti)8O16, M=Al, Fe and Mg) were grown from melts. Despite of the wide range of the solid solution the composition of all the single crystals obtained was around x=1.5. The prismatic faces of K–Al– and K–Mg-priderite consisted mainly of planes {100} with small {110} and those of K-Fe-priderite consist mainly of {110} with small {100}. The terminal faces of the crystals were made up of vicinal faces with irregular interfacial angle. The cleavage of the crystals was parallel to {110} on each priderite. Pleochroism of K–Al-priderite: O-colorless, E-blue; K–Fe-priderite: O-dark brown, E-dark brown with blue; K–Mg-priderite: O-pale blue, E-dark blue. The optical properties of Al2TiO5 and MgTi2O5 crystals included in priderite single crystals were also described.

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