Carbobystrite, ideally Na8[Al6Si6O24](CO3)·4H2O, trigonal, a 12.6678(5), c 10.3401(4) Å, V 1437.0(2) Å3, c:a = 0.8162, space group P31c, Z = 2, R = 0.0271 (for 4861 observed reflections collected with a four-circle X-ray diffractometer), is a new cancrinite-group mineral species from Mount Koashva, Khibina alkaline massif, Kola Peninsula, Russia. It formed in a pegmatitic environment. Associated minerals are: microcline, sodalite, megakalsilite, natrolite, pectolite, aegirine, natrite, nacaphite, vitusite-(Ce), fluorcaphite, belovite-(Ce), umbite, lemmleinite-K, lomonosovite, lovozerite, phlogopite, sphalerite and galena. The mineral was found in only one hand specimen of pegmatite as a corroded irregularly shaped grain about 3 mm across, intergrown with sodalite, megakalsilite and natrite. It is transparent, colorless with a white streak, a vitreous luster, and fluoresces pale yellow under ultraviolet light. Carbobystrite has a Mohs hardness of 6, is brittle with a conchoidal fracture, and has no cleavage. The calculated density is 2.366 g/cm3. Carbobystrite is uniaxial negative, non-pleochroic, 1.500(2), 1.488 (2). The strongest six reflections in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 4.689(100)(012), 3.249(100)(32, 122), 6.378(80) (20), 2.661(80)(041, 123, 133), 3.867(70)(31, 121), and 3.664(70)(030). An electron-microprobe analysis gives Na2O 22.66, K2O 1.75, SiO2 35.74, Al2O3 30.42, CO2 4.37, H2O 6.26, sum 101.20 wt.%, with CO2 and H2O calculated from structural data. The empirical formula (based on O = 30.5 atoms per formula unit) is (Na7.40K0.38)7.78(Al6.04Si6.02)12.06O24(CO3)·3.5H2O; the simplified formula is Na8[Al6Si6O24](CO3)·4H2O. The name carbobystrite denotes the compositional relation between the new mineral and bystrite, (Na,K)7Ca[Al6Si6O24](S)1.5·H2O; they are related by the substitution Na+ + (CO3)2- + 2.5H2O Ca2+ + (S2-)1.5. The framework of Si,Al-O tetrahedra can be described as an ABAC stacking sequence. In the crystal struc
Carbobystrite, Na8(Al6Si6O24)(CO3) . 4H2O, a new cancrinite-group mineral species from the Khibina alkaline massif, Kola peninsula, Russia: description and crystal structure.
2010
Abstract
Carbobystrite, ideally Na8[Al6Si6O24](CO3)·4H2O, trigonal, a 12.6678(5), c 10.3401(4) Å, V 1437.0(2) Å3, c:a = 0.8162, space group P31c, Z = 2, R = 0.0271 (for 4861 observed reflections collected with a four-circle X-ray diffractometer), is a new cancrinite-group mineral species from Mount Koashva, Khibina alkaline massif, Kola Peninsula, Russia. It formed in a pegmatitic environment. Associated minerals are: microcline, sodalite, megakalsilite, natrolite, pectolite, aegirine, natrite, nacaphite, vitusite-(Ce), fluorcaphite, belovite-(Ce), umbite, lemmleinite-K, lomonosovite, lovozerite, phlogopite, sphalerite and galena. The mineral was found in only one hand specimen of pegmatite as a corroded irregularly shaped grain about 3 mm across, intergrown with sodalite, megakalsilite and natrite. It is transparent, colorless with a white streak, a vitreous luster, and fluoresces pale yellow under ultraviolet light. Carbobystrite has a Mohs hardness of 6, is brittle with a conchoidal fracture, and has no cleavage. The calculated density is 2.366 g/cm3. Carbobystrite is uniaxial negative, non-pleochroic, 1.500(2), 1.488 (2). The strongest six reflections in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 4.689(100)(012), 3.249(100)(32, 122), 6.378(80) (20), 2.661(80)(041, 123, 133), 3.867(70)(31, 121), and 3.664(70)(030). An electron-microprobe analysis gives Na2O 22.66, K2O 1.75, SiO2 35.74, Al2O3 30.42, CO2 4.37, H2O 6.26, sum 101.20 wt.%, with CO2 and H2O calculated from structural data. The empirical formula (based on O = 30.5 atoms per formula unit) is (Na7.40K0.38)7.78(Al6.04Si6.02)12.06O24(CO3)·3.5H2O; the simplified formula is Na8[Al6Si6O24](CO3)·4H2O. The name carbobystrite denotes the compositional relation between the new mineral and bystrite, (Na,K)7Ca[Al6Si6O24](S)1.5·H2O; they are related by the substitution Na+ + (CO3)2- + 2.5H2O Ca2+ + (S2-)1.5. The framework of Si,Al-O tetrahedra can be described as an ABAC stacking sequence. In the crystal strucI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
