Feldspars bytownite

The first single-mineral dissolution experiments to utilize radiogenic isotopes investigated the dissolution of the feldspars bytownite, microcline, and albite in flow-through cells at a pH 3 and at 25 °C (Brantley et al., 1998). Solutions from major element experiments (Stillings and Brantley, 1995) were reanalyzed for strontium and rubidium concentrations and Sr/ Sr ratios with the goal of... 

Plagioclase feldspars Albite, oligoclase, andesine, labradorite, bytownite, anorthite... 

Nord, G. L., Heuer, A. H., Lally, J. S. (1974). Transmission electron microscopy of substructures in Stillwater bytownites. In The Feldspars, edited by W. S. MacKenzie and J. Zussman, pp. 522-35. Manchester Manchester University Press. 

Release of trace elements such as strontium from feldspar is also observed to be nonstoichio-metric (Brantley et al, 1998). At pH 3, bytownite, microcline, and albite aU release strontium at an initially fast rate that slows to near stoichiometric values at steady state. In addition, aqueous strontium is enriched in Sr compared to the bulk mineral early in dissolution. All feldspars smdied evenmally released strontium in isotopic abundance roughly equal to that of the bulk mineral. Nonstoichiometric release of strontium was explained by the presence of defects or accessory phases in the minerals. Taylor et al. (2000) also reported that the initial dissolution of labradorite was nonstoichiometric during dissolution in column reactors with inlet solution pH 3, but that the mineral dissolved and released strontium stoichiometrically at steady state. In contrast to the earlier work, however, Sr/ Sr in solution did not differ from that of the bulk labradorite during dissolution in the column experiments. 

Rate equations for the dissolution of feldspar in the presence of organic ligands have been proposed and have been related to surface complexation at the feldspar surface (Stillings et al., 1996 Welch and Ullman, 2000). These latter workers also report that the apparent activation energy of silica release from bytownite decreases from —lOkcalmol to 7kcalmol in the presence of oxalate and gluconate in neutral solutions (Welch and UUman, 2000). 

Welch S. A. and Ullman W. J. (1999) The effect of microbial glucose metabolism on bytownite feldspar dissolution rates between 5 degrees and 35 degrees C. Geochim. Cosmochim. Acta 63, 3247-3259. 

Welch S. and Ullman W. J. (2000) The temperature dependence of bytownite feldspar dissolution in neutral aqueous solutions of inorganic and organic ligands at low temperature (5-35 °C). Chem. Geol. 167, 337-354. 

The most abundant mineral in the rocks of the main body of the Basement sill studied by Hamilton (1965) is calcic plagioclase feldspar (labradorite-bytownite). 

Aluminium group Feldspar group Silicates group Aualcime Andesine Anorthite Bytownite Kaolinite Labradorite Montmoiillonite Oligoclase... 

Bytownite is a member of the feldspar group q.v) of minerals with a composition between that of albite and anorthite (qq.v). It is thus... 

Bytownite is a member of the plagioclase feldspar series. These minerals readily degrade to clay group minerals (q.v.) and zeolites in the presence of water and may occur as relict minerals in artists materials. 

Feldspar group (Framework silicates) Albite Andesine Anorthite Anorthoclase Bytownite Labradorite Microcline Oligoclase Orthoclase. 

FELDSPAR. The most common mineral in crystalline rocks. Hardness 6.0-6.5 Mohs. Usually occurs as small grains intimately associated with other minerals, but commercial deposits are obtained from pegmatites. Feldspars form a group of which the principal types are potash spar (ortho-clase, microcline), soda spar (alhite), lime spar (anorthite), and lime-soda spar (ohgo-clase, andesine, labradorite and bytownite). They are aluminum sdicates of potassium, sodium and calcium. 

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