Grenmarite, a new mineral of the gö tzenite-seidozerite-rosenbuschite group, was found in a syenite pegmatite at the eastern side of the island Vesle Arøya in the Langesundsfjord district, Norway. Grenmarite, ideally (Zr,Mn) 2(Zr,Ti)(Mn,Na) (Na,Ca)4(Si2O 7)2(O,F)4, is the Zr-analogue of seidozerite. It is monoclinic with space group P2/c, Z = 2, a = 5.608(1), b = 7.139(1), c = 18.575(5) Å, β = 102.60(2)° and V = 725.72(3) Å3. It occurs as yellowish brown, semi-parallel aggregates of elongated, flattened crystals up to 1 cm in length. The mineral is translucent, with vitreous lustre, good {001} cleavage and uneven fracture. Mohs' hardness is 41/2; the measured density is 3.49(1) g/cm3. The strongest five X-ray diffraction lines of the powder pattern [d in Å (I)] are: 2.898(100), 3.027(68), 2.613(26), 2.459(24), 1.853(24). An average of fifteen electron microprobe analyses of grenmarite gave SiO2 29.85, TiO2 4.51, CaO 1.84, MnO 8.25, FeO 2.01, Na 2O 15.43, Y2O3 0.22, Ce 2O3 0.01, ZrO2 31.63, Nb 2O5 0.06, F 5.24, O ≡ F 2.21, total 96.84 wt.%. The empirical formula, based on 4 Si atoms, is (Zr 1.52Mn0.46Y0.02)∑2.00 (Zr0.55Ti0.45)∑1.00(Mn 0.48Na0.29Fe0.23)∑1.00 (Na3.72Ca0.26)∑3.98 Si 4O15.40F2.22. Grenmarite is isostructural with seidozerite: its structure can be described as built up with three distinct modules connected through corner-sharing: an "octahedral" layer, an "octahedral" ribbon, and disilicate groups. The crystal structure has been refined to a final R of 0.043. The crystal chemical formula resulting from the structural refinement is: (Zr1.76Mn0.24)∑2.00 Zr0.54Ti0.46)∑1.00 (Mn0.76Na0.24)∑1.00(Na 3.32Ca0.38Mn0.30)∑4.00 (Si2O7)2O1.96F 2.04.
Grenmarite, a new member of the götzenite-seidozerite-rosenbuschite group from Langesundsfjord district: definition and crystal structure
MERLINO, STEFANO;PERCHIAZZI, NATALE
2004-01-01
Abstract
Grenmarite, a new mineral of the gö tzenite-seidozerite-rosenbuschite group, was found in a syenite pegmatite at the eastern side of the island Vesle Arøya in the Langesundsfjord district, Norway. Grenmarite, ideally (Zr,Mn) 2(Zr,Ti)(Mn,Na) (Na,Ca)4(Si2O 7)2(O,F)4, is the Zr-analogue of seidozerite. It is monoclinic with space group P2/c, Z = 2, a = 5.608(1), b = 7.139(1), c = 18.575(5) Å, β = 102.60(2)° and V = 725.72(3) Å3. It occurs as yellowish brown, semi-parallel aggregates of elongated, flattened crystals up to 1 cm in length. The mineral is translucent, with vitreous lustre, good {001} cleavage and uneven fracture. Mohs' hardness is 41/2; the measured density is 3.49(1) g/cm3. The strongest five X-ray diffraction lines of the powder pattern [d in Å (I)] are: 2.898(100), 3.027(68), 2.613(26), 2.459(24), 1.853(24). An average of fifteen electron microprobe analyses of grenmarite gave SiO2 29.85, TiO2 4.51, CaO 1.84, MnO 8.25, FeO 2.01, Na 2O 15.43, Y2O3 0.22, Ce 2O3 0.01, ZrO2 31.63, Nb 2O5 0.06, F 5.24, O ≡ F 2.21, total 96.84 wt.%. The empirical formula, based on 4 Si atoms, is (Zr 1.52Mn0.46Y0.02)∑2.00 (Zr0.55Ti0.45)∑1.00(Mn 0.48Na0.29Fe0.23)∑1.00 (Na3.72Ca0.26)∑3.98 Si 4O15.40F2.22. Grenmarite is isostructural with seidozerite: its structure can be described as built up with three distinct modules connected through corner-sharing: an "octahedral" layer, an "octahedral" ribbon, and disilicate groups. The crystal structure has been refined to a final R of 0.043. The crystal chemical formula resulting from the structural refinement is: (Zr1.76Mn0.24)∑2.00 Zr0.54Ti0.46)∑1.00 (Mn0.76Na0.24)∑1.00(Na 3.32Ca0.38Mn0.30)∑4.00 (Si2O7)2O1.96F 2.04.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
