Kassite [CaTi2O4(OH)2] is a rare mineral typically found in silica-undersaturated environments. Localities where it was previously recognized include the Afrikanda alkaline-ultrabasic complex in Kola Peninsula (Russia), Magnet Cove alkaline complex (Arkansas) and an ultrabasic Fe-ore deposit in Wuyang (Henan, China). Identification of kassite is not trivial because it is dimorphous with cafetite, and can be easily confused with titanite, perovskite or TiO2 polymorphs during a routine petrographic examination. The primary objective of the present study was to determine the nature of Ca-Ti oxide phases commonly observed to replace perovskite in alkaline and carbonate-rich rocks (including carbonatites, kimberlites and nephelinites). For detailed analysis, we selected relatively large (100 ?m - 1 mm) grains of hydrous Ca-Ti oxide from silicocarbonatite from the Prairie Lake complex (Ontario) and serpentine-calcite kimberlite from Iron Mountain (Wyoming). Both samples were examined using electron-microprobe analysis, Raman micro-spectroscopy and X-ray micro-diffraction. For comparison, cafetite from Khibiny (Kola, Russia) was investigated using the same techniques. Our data show that the major product of perovskite alteration in a CO2-rich environment (prior to the development of anatase and/or ilmenite) is kassite, i.e. a monoclinic (space group P21/a) polymorph of CaTi2O4(OH)2. The refined cell parameters of the Prairie Lake material are: a= 5.285(1) Å, b= 8.990(2) Å, c= 9.549(3) Å, and ?: 90.42(2)°. This mineral can be readily distinguished on the basis of its Raman spectrum, which contains well-defined lines at 169, 219, 340, 440, and 695 cm-1 not observed in its dimorphous cafetite. In addition to providing constraints on the conditions of peroskite alteration in CO2-rich systems, the present study has implications for safe disposal of fission products in perovskite-based ceramics and applicability of radiometric and other isotopic data obtained on perovskite concentrates.
Kassite from the Prairie Lake (Ontario) and Iron Mountain (Wyoming) and its relation to perovskite alteration
Medici L
2011
Abstract
Kassite [CaTi2O4(OH)2] is a rare mineral typically found in silica-undersaturated environments. Localities where it was previously recognized include the Afrikanda alkaline-ultrabasic complex in Kola Peninsula (Russia), Magnet Cove alkaline complex (Arkansas) and an ultrabasic Fe-ore deposit in Wuyang (Henan, China). Identification of kassite is not trivial because it is dimorphous with cafetite, and can be easily confused with titanite, perovskite or TiO2 polymorphs during a routine petrographic examination. The primary objective of the present study was to determine the nature of Ca-Ti oxide phases commonly observed to replace perovskite in alkaline and carbonate-rich rocks (including carbonatites, kimberlites and nephelinites). For detailed analysis, we selected relatively large (100 ?m - 1 mm) grains of hydrous Ca-Ti oxide from silicocarbonatite from the Prairie Lake complex (Ontario) and serpentine-calcite kimberlite from Iron Mountain (Wyoming). Both samples were examined using electron-microprobe analysis, Raman micro-spectroscopy and X-ray micro-diffraction. For comparison, cafetite from Khibiny (Kola, Russia) was investigated using the same techniques. Our data show that the major product of perovskite alteration in a CO2-rich environment (prior to the development of anatase and/or ilmenite) is kassite, i.e. a monoclinic (space group P21/a) polymorph of CaTi2O4(OH)2. The refined cell parameters of the Prairie Lake material are: a= 5.285(1) Å, b= 8.990(2) Å, c= 9.549(3) Å, and ?: 90.42(2)°. This mineral can be readily distinguished on the basis of its Raman spectrum, which contains well-defined lines at 169, 219, 340, 440, and 695 cm-1 not observed in its dimorphous cafetite. In addition to providing constraints on the conditions of peroskite alteration in CO2-rich systems, the present study has implications for safe disposal of fission products in perovskite-based ceramics and applicability of radiometric and other isotopic data obtained on perovskite concentrates.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
