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Showing papers in "American Mineralogist in 1968"



Journal Article
TL;DR: In this paper, a 3D least-squares X-ray diffraction analysis of forsterite (Mgo.9o,Feo Jo), plutonic hyalosiderite (mg0.,., Feo 456, Mno oo6,Cao.o1), and fayalite (Fe0 ••,,Mgo_04,Mno o•l · the closeness in value of the isotropic temperature factors calculated for the M sites indicates substitutional disorder of the Mg and Fe atoms in all
Abstract: Atomic parameters were obtained by 3D least-squares X-ray diffraction analysis of forsterite (Mgo.9o,Feo Jo), plutonic hyalosiderite (Mg0 .,., Feo 456, Mno oo6,Cao.oo2), dike hortonolite (Mgo.<9,Feo ,.,Mno o1,Cao.o1), and fayalite (Fe0 •• ,,Mgo_04,Mno o•l · The closeness in value of the isotropic temperature factors calculated for the M sites indicates substitutional disorder of the Mg and Fe atoms in all four structures. Polyhedra distortions are closely similar in all four structures showing that they depend on the struc­ ture type rather than on the Mg, Fe substitution. Simple electrostatic rules allied with pa. ck­ ing considerations permit qualitative explanation of the structural distortions. The M(l) octahedron has six short shared edges to give a distorted and elongated trigonal antiprism. The M(2) octahedron has a triangle of three short shared edges. Metal-oxygen distances tend to compensate e.g., the longest Si-0 distance and the shortest (Mg,Fe)-0 distance go to the same oxygen.

202 citations













Journal Article
TL;DR: In this article, six eclogite inclusions in kimberlite of Roberts-Victor mine near Kimberley, South Africa, three of them are essentially bimineralic Eclogites consisting of clinopyroxene and pyroperich garnet.
Abstract: Of six eclogite inclusions in kimberlite of Roberts-Victor mine near Kimberley, South Africa, three are essentially bimineralic eclogites consisting of clinopyroxene and pyroperich garnet, and others contain phlogopite in addition to clinopyroxene and garnet. Clinopyroxenes are omphacites ranging in composition from a jadeite-poor variety (jadeite 9.9 mole 7) to a jadeite-rich variety (40.8%). Garnet ranges in composition from grossular 2.9 to 18.1 percent. Partition of Mg and Fe2+ between coexisting garnet and clinopyroxene in these eclogites is similar to those in the eclogites from other kimberlite pipes, but much difierent from those in eclogites from various metamorphic terrains, indicating that the physical conditions of their formation are different; eclogites in kimberlite were equilibrated in the upper mantle. Phlogopite in eclogites were probably formed within the upper mantle before the eruption of kimberlite. The compositions of the eclogites correspond to those of olivine basait or picrite basalt, although KrO content is considerably higher in two of them. As the Fe'z+/(Mgf Fe2+) ratio of the eclogite increases, AhOs of the eclogite increases, content oi jadeite in clinopyroxene and content of grossular in garnet increase. These reiations may be interpreted as due to the difierence in degree of partial melting of the mantle material (e.g., garnet peridotite) when the eclogite magmas were formedl magmas of lower degree of partial melting have higher Fe'z+/(Mg*Fe'+) ratio and higher jadeite and grossular components' whereas those of higher degree of partial melting approach the garnet peridotite in composition, having lower Fe'z+/(MgfFe'z+) ratio and Iower jadeite and grossular components. Also these systematic chemical variations in eclogites, clinopyroxenes, and garnets may be due to crystallization of picritic magma at high pressures; earlier crystallization products correspond to eclogites having lower p\"z+1Mgf Fe2+) ratios and lower jadeite and lower grossular components.















Journal Article
TL;DR: The model of McConnell (1960) for carbonate apatites fits these data most closely as mentioned in this paper, suggesting that two (CO 3 ) 2- sites exist, one of which is asymmetrical.
Abstract: Fossil bone exhibits an increase in flourine over modern mammalian (3% vs. 0.18%), but CO 2 (3.7% vs. 4.4%) and H 2 O (5. 36% vs. 6%) are essentially the same. Heating of fossil bone, modern bone, and carbonate-bearing apatites to 1250 degrees produces no separation. CaO phase is detectable by X-ray diffraction, but Na is subsequently leached preferentially. The IR spectrograms provide no evidence of physically discrete CO 2 -bearing phases in carbonate apatites and fossil bones. The (CO 3 ) - v 3 vibration in the 7 region shows a bidentate or tridentate split, even in apatite from Renfrew, containing only 0.75% CO 2 , suggesting that two (CO 3 ) 2- sites exist, one of which is asymmetrical. The model of McConnell (1960) for carbonate apatites fits these data most closely. -- AATA