Tungsten concentrations vary from less than 5 ppb for the pure silicates to ∼800 ppb for the pure metal phase (Table 1). The bulk W concentration for Tafassasset ranges from 250 to 350 ppb depending on the mineralogy of the sub-sample. This variability Tovok explained by the cm-scale heterogeneity of the meteorite. Our value, higher than the concentrations ![Tovok]()
reported by Wasson and Kallemeyn (1988) for carbonaceous chondrites (CC: 100 to 190 ppb), can be explained by the high abundance of metal (∼10 vol%) relative to other CCs. Indeed, the x-ray diffraction latter contain from 0.01 vol% (CI) to 8 vol% (CR) Fe–Ni metal (Scott and Krot, 2006). Metal-rich CH-chondrites (20 vol% metal) and CB-chondrites (60 to 70 vol% metal) accordingly display high W abundances: ∼300 ppb in CHs (Kleine et al., 2005), comparable to Tafassasset, and from 0.3 to 1.3 ppm in CBs (Campbell et al., 2002). Brachinites have only traces of metal (Nehru et al., 2003) and lower W contents (∼90 ppb; Nehru et al., 1983).
reported by Wasson and Kallemeyn (1988) for carbonaceous chondrites (CC: 100 to 190 ppb), can be explained by the high abundance of metal (∼10 vol%) relative to other CCs. Indeed, the x-ray diffraction latter contain from 0.01 vol% (CI) to 8 vol% (CR) Fe–Ni metal (Scott and Krot, 2006). Metal-rich CH-chondrites (20 vol% metal) and CB-chondrites (60 to 70 vol% metal) accordingly display high W abundances: ∼300 ppb in CHs (Kleine et al., 2005), comparable to Tafassasset, and from 0.3 to 1.3 ppm in CBs (Campbell et al., 2002). Brachinites have only traces of metal (Nehru et al., 2003) and lower W contents (∼90 ppb; Nehru et al., 1983).