Isamu Shinno

A Mössbauer study of ferric iron in olivine

Natural and synthetic olivines with ferrous and ferric iron have been studied by Mössbauer spectroscopy. Their spectra exhibit three superimposed quadrupole-split doublets corresponding to Fe2+ at M1 and M2 sites and Fe3+ at an unidentified position, which is probably M2. The hyperfine parameters of Fe3+ at temperatures between 300°C and 450°C are: Δ=0.67–1.23 mm/s, δ=0.04–0.23 mm/s relative to metallic iron, and the full width at half height, HW=0.15–0.43 mm/s.The Fe2+ populations of M2 decrease with increasing Fe3+ content. However, Fe2+ prefers M1 in synthetic olivines, even at high temperatures (800°–1,400°C). In kirschsteinite, Fe2+ and Fe3+ are exclusively in M1. Fe2+/Fe3+ ratios estimated from the peak areas are consistent with chemical analyses.

Chemical composition and radioactivity in hokutolite (plumbian barite) collected at Peito hot spring, Taiwan

Abstract Chemical composition and radionuclide concentrations were determined for hokutolite, plumbian barite, collected at Peito hot spring, Taiwan. The hokutolite, precipitated on the surface of the base rock, was scraped into 20 layers from the surface. Barium and Pb were determined by inductively coupled plasma-atomic emission spectroscopy, and 228Ra, 226Ra and 210Pb were determined by γ-ray spectrometry. Comparison of the 228 Ra 226 Ra activity ratio at the surface of the hokutolite with that of the hot spring water suggests that the hokutolite has been isolated from the stream for 60 years. Significantly low fractions of (Ba, Pb)SO4 and changes in Ba Pb mole ratio in the middle layers of the hokutolite suggest a change of growth condition at that time. Using the smooth and continuous decline in 228 Ra 226 Ra activity ratio observed in the upper layers of the hokutolite, the growth rate of 0.17 mm year−1 was estimated.

57Fe Mössbauer study of pumpellyiteokhotskite-julgoldite series minerals

SummaryFe and Mn distribution in the pumpellyite group minerals (W8X4Y8Z12056-n(OH)n) has been studied by using57Fe Mössbauer spectroscopy. The studied Fe-pumpellyites, belonging to the pumpellyite-julgoldite series, were collected from two localities; metabasites in the Tokoro belt, Hokkaido, and gabbroic sills in the Shimane Peninsula, Japan. Okhotskite, an Mn3+-dominant pumpellyite group mineral, was separated from the ores of metamorphosed manganiferous iron ore deposits in the Tokoro belt.57Fe Mössbauer spectrum of Tokoro Fe-pumpellyite is composed of two Fe2+- and two Fe3+-doublets. On the basis of the single crystal structure refinements of Al-pumpellyites published so far, doublets were assigned to FeW2+(IS= 1.01 andQS = 2.73 mm/s), FeX2+ (IS = 0.97 andQS = 3.18 mm/s), FeX3+ (IS = 0.29 andQS =1.37 mm/s) and FeY3+ (IS = 0.36 andQS = 2.09 mm/s), whereIS is isomer shift relative to a metallic iron absorber andQS is quadrupole splitting. The Mössbauer spectrum of the Mitsu Fepumpellyite is composed of three doublets assigned to FeX2+ (IS= 1.14 andQS = 3.20 mm/s), FeX3+ (IS = 0.36 andQS =1.13 mm/s) and FeY3+(IS = 0.37 andQS= 1.93 mm/s). These assignments show strong preference of Fe3+ in the X-site. The Mössbauer spectrum of the okhotskite is composed of two doublets by FeX3+ (IS= 0.37 andQS = 1.13 mm/s) and FeY3+ (IS = 0.42 andQS = 2.18 mm/s). The area ratio shows that FeX3+:FeY3+ ratio is 94:6. On the basis of chemical and Mössbauer analyses, MnX3+:MnY3+ ratio is given as 19:81, indicating stronger Y-site preference of Mn3+ than Fe3+, what is consistent with Jahn-Teller theory. Al, Mn3+ and Fe3+ prefer the Y-site in this order.ZusammenfassungDie Fe- und Mn-Verteilung in Mineralen der Pumpellyit-Gruppe (W8X4Y8Z12O56-n(OH)n) wurde mittels Mössbauer-Spektroskopie studiert. Die untersuchten Fe-Pumpellyite der Pumpellyit-Julgoldit-Serie stammen von zwei verschiedenen japanischen Lokalitäten: von Metabasiten des Tokoro-Gürtels, Hokkaido, und von Gabbro-Sills der Shimane Halbinsel. Okhotskit, ein Mn3+-dominiertes Mineral der Pumpellyit-Gruppe, wurde aus Erzen einer Mn-führenden Eisenerzlagerstätte des Tokoro-Gürtels separiert. Das57Fe Mössbauer-Spektrum der Tokoro Fe-Pumpellyite zeigt zwei Fe2+- und zwei Fe3+-Doubletten. Auf Grund bisher publizierter verfeinerter Einkristall-Strukturuntersuchungen von Al-Pumpellyiten werden diese Doubletten folgendermaßen zugeordnet: FeW2+ (IS = 1.01 undQS = 2.73 mm/s), FeX2+(IS = 0.97 undQS = 3.18 mm/s), FeX3+ (IS = 0.29 undQS =1.37 mm/s) und FeY3+ (IS = 0.36 undQS = 2.09 mm/s).IS bezeichnet dabei die Isomer-Shift relativ zu einem metallischen Eisenabsorbenten,QS das Quadrupole-Splitting. Diese Zuordnungen belegen den bevorzugten Einbau von Fe3+ in die X-Position. Das Mössbauer-Spektrum von Okhotskit zeigt zwei Doubletten bei FeX3+ (IS = 0.37 undQS = 1.13 mm/s) und FeY3+ (IS = 0.42 undQS = 2.18 mm/s). Das Flächenverhältnis zeigt, daß das Verhältnis FeX3+:FeY3+ 94:6 ist. Auf Grund der chemischen und der Mössbauer-Analysen wird das MnX3+:MnY3+ Verhältnis mit 19:81 angegeben. Mn3+ zeigt somit eine stärkere Präferenz für die Y-Position als Fe3+, ein Resultat, das mit der Jahn-Teller-Theorie konsistent ist. Der bevorzugte Einbau in die Y-Position ist, in dieser Reihenfolge, Al>Mn3+>Fe3+.

The distribution of Fe3+ and Ga3+ between two tetrahedral sites in melilites, Ca2(Mg, Fe3+, Ga, Si)3O7

The distribution of Fe3+ and Ga3+ between the two tetrahedral sites in three synthetic melilites has been studied by using 57Fe Mössbauer spectroscopy. In the melilite, (Ca2Ga2SiO7)50 (Ca2Fe3+GaSiO7)50 (mol %), the distribution of Fe3+ and Ga3+ in T1 and T2 sites is apparently random, which can be explained in terms of the electrostatic valence rule. However in the melilites, (Ca2MgSi2O7)52 (Ca2Fe3+GaSiO7)42 (Ca2Ga2SiO7)6 and (Ca2MgSi2O7)62 (Ca2Fe3+GaSiO7)36 (Ca2Ga2SiO7)2 (mol %), Fe3+ shows preference for the more ionic T1 site and Ga3+ for the more covalent T2 site. If the electronegativity of Ga3+ is assumed to be larger than that of Fe3+, the mode of distribution of Fe3+ and Ga3+ can be explained in terms of our previous hypothesis that a large electronegativity induces a stronger preference for the more covalent T2 site.