Chromium abundance data

Wide variations of 5°Cr/54Cr are expected within presolar grains, and perhaps also in the ratio 5°Cr/52Cr but the small chromium abundance within the grains has rendered the measurement impractical so far. Also, the 5°Cr/52Cr ratio is often assumed to be normal in order that corrections for mass-dependent fractionation can be made. Such normalization suppresses manifestvariability in 5°Cr but of course itcan be recovered from the data if one selects some other assumption about the mass fractionation. 

Figure 13 Trace-element ratios in IDPs. Data from synehrotron X-ray fluoreseenee analyses are plotted on three element diagrams. Element ratios are normalized to bulk Cl abundances (element/Fe)sampie/(element/Fe)ci also denoted element/Fe/CL Cl eomposition lies at the point element/Fe/CI = 1 on eaeh plot. Averages, assuming data are normally distributed (open squares) and assuming the data are log normally distributed (open diamonds), are also shown. Plots (a)-(c) exhibit the behavior of some more refractory elements chromium, calcium, and titanium with respect to nickel, while (d) and (e) show the behavior of zine (relatively volatile) with respect to nickel (relatively refractory) and selenium (relatively volatile) (source Kehm et aL, 2002).

Chemical leach tests of the <50 p.m size fraction of dust samples collected around Owens Lake, using water (Reheis etal, 2001, and our unpublished data) and SLFs (our unpubhshed data), show that the dusts are sufficiently aUcahne and reactive to shift the pH of water and SLF to values near 10.5 and 9.5, respectively. Arsenic, chromium, vanadium, molybdenum, hthium, zinc, and other trace metals or metalloids are readily solubilized from the dusts. The trace metals or metalloids leached in the greatest quantities are those that form oxyanion species or abundant carbonate complexes in solution, and that are therefore mobilized most effectively under the alkaline conditions generated by the alkaline dusts. 

You calculate the atomic weight of an element by multiplying each isotopic mass by its fractional abundance and sununing the values. If you do that for neon using the data given here, you will obtain 20.179 amu. The next example illustrates the calculation in full for chromium. 

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