Ecandrewsite – Zincian Pyrophanite from Lujavrite, Pilansberg Alkaline Complex, South Africa
نویسندگان
چکیده
Ilmenite-group titanates are relatively common accessory minerals in agpaitic nepheline syenite (lujavrite) in the Pilansberg alkaline complex, South Africa. They crystallized in three generations and form a continuous ecandrewsite – pyrophanite solidsolution extending from (Zn0.81Mn0.12Fe0.07)TiO3 to (Mn0.93Fe0.7)TiO3. The earliest generation of ferroan manganoan ecandrewsite of widely varying composition (Zn0.81–0.53Mn0.33–0.12Fe0.11–0.04)TiO3 is replaced by zincian pyrophanite (Mn0.82–0.34Zn0.50– 0.20Fe0.13–0.06)TiO3. The latest generation is pyrophanite with only traces of zinc, showing a compositional evolution toward ferroan pyrophanite. The three generations of Zn–Mn titanates recognized on the basis of their paragenesis and composition crystallized during the subsolidus alteration of the lujavrite by evolving deuteric alkaline fluids. The enrichment in Zn, Mn, and Ti in these fluids resulted from the decomposition of earlier-formed magmatic-stage Znand Mn-bearing titanoand zirconosilicates. This is the first reported occurrence of a near-complete ecandrewsite – pyrophanite (ZnTiO3 – MnTiO3) solidsolution series.
منابع مشابه
THE PYROPHANITE – ECANDREWSITE SOLID - SOLUTION : CRYSTAL STRUCTURES OF THE Mn 1 – xZnxTiO 3 SERIES ( 0 . 1 ≤ x ≤ 0 . 8 )
The crystal structure of members of the pyrophanite–ecandrewsite solid-solution series, Mn1–xZnxTiO3 (0.1 ≤ x ≤ 0.8 apfu), synthesized by ceramic methods in air at ambient pressure, has been characterized by Rietveld analysis of powder X-ray-diffraction patterns. All of these compounds crystallize with the ilmenite structure and adopt space group R3̄. The maximum solubility of Zn in MnTiO3 is co...
متن کاملA new class of Cu/ZnO catalysts derived from zincian georgeite precursors prepared by co-precipitation.
Zincian georgeite, an amorphous copper-zinc hydroxycarbonate, has been prepared by co-precipitation using acetate salts and ammonium carbonate. Incorporation of zinc into the georgeite phase and mild ageing conditions inhibits crystallisation into zincian malachite or aurichalcite. This zincian georgeite precursor was used to prepare a Cu/ZnO catalyst, which exhibits a superior performance to a...
متن کاملA new class of Cu/ZnO catalysts derived from zincian georgeite precursors prepared by co-precipitation† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc04130b Click here for additional data file.
Zincian georgeite, an amorphous copper–zinc hydroxycarbonate, has been prepared by co-precipitation using acetate salts and ammonium carbonate. Incorporation of zinc into the georgeite phase and mild ageing conditions inhibits crystallisation into zincian malachite or aurichalcite. This zincian georgeite precursor was used to prepare a Cu/ZnO catalyst, which exhibits a superior performance to a...
متن کاملMolecular characterization and DNA methylation profile of Libyodrilus violaceous from oil polluted soil
Studies on earthworms using molecular markers are rare in Africa except a handful from South Africa. Reports on Libyodrilus violaceous,an earthworm found in West Africaare available including their metal tolerance and bioaccumulation capacity but their molecular characterization and ecotoxicology studies are scarce. In this study, triplicate L. violaceous specimens were collec...
متن کاملChemical Composition and Antibacterial Activity of Essential Oil of Cosmos bipinnatus Cav. Leaves from South Africa
The chemical composition of essential oils isolated from the leaves of Cosmos bipinnatus and its antibacterial activity were analyzed by GC-MS and microbroth dilution assay respectively. The essential oil extracted from this plant was predominantly composed of monoterpenes (69.62%) and sesquiterpenes (22.73%). The antibacterial assay showed that the oil had significant inhibitory effects agains...
متن کامل