Table 2.
Linear combination fit results from Fe K-edge XANES and EXAFS.
| XANES (E range 7110-7165 eV) | EXAFS (k range 2.5-10.8 Ǻ−1) | ||||
|---|---|---|---|---|---|
| Sample | Standard a | Fit % (±) b | Normalized % | Fit % (±) b | Normalized % |
| LAX1 | Fer | 51.3 (1.8) | 51.8 | 41.8 (2.5) | 37.9 |
| Hem | 19.5 (2.2) | 19.7 | 25.6 (0.9) | 23.2 | |
| Mag | 9.5 (0.7) | 9.6 | 17.8 (1.7) | 16.1 | |
| Il/Sm | 18.8 (2.0) | 19 | 25.3 (2.2) | 22.9 | |
| Sum | 99.0 | 110.4 | |||
| R-factor c | 0.0001346 | 0.0202 | |||
| Red. χ2 d | 0.0000349 | 0.144 | |||
| LAX2 | Fer | 43.2 (1.6) | 43.5 | 39.7 (2.7) | 36.2 |
| Hem | 19.7 (2.1) | 19.9 | 25.7 (1.0) | 23.4 | |
| Mag | 14.5 (0.6) | 14.6 | 23.4 (1.8) | 21.3 | |
| Il/Sm | 21.8 (1.9) | 22.0 | 21.0 (2.3) | 19.1 | |
| Sum | 99.2 | 109.8 | |||
| R-factor c | 0.000118 | 0.0244 | |||
| Red. χ2 d | 0.0000298 | 0.168 | |||
| USC2 | Fer | 41.7 (2.4) | 42.1 | 35.0 (2.3) | 34.2 |
| Hem | 12.5 (2.6) | 12.6 | 22.9 (0.8) | 22.4 | |
| Mag | 22.8 (1.9) | 23.0 | 24.4 (1.4) | 23.9 | |
| Il/Sm | 16.4 (3.3) | 16.5 | 17.7 (1.9) | 17.3 | |
| Fe(0) Metal | 5.7 (0.7) | 5.8 | 2.3 (0.4) | 2.2 | |
| Sum | 99.1 | 102.3 | |||
| R-factor c | 0.000236 | 0.0183 | |||
| Red. χ2 d | 0.0000542 | 0.106 | |||
a
Abbreviations: Fer - Ferrihydrite, Hem - Hematite, Mag - Magnetite, Il/Sm – Illite/smectite. See Table S2 for details of reference compound spectra.
b
Estimated uncertainties (in parentheses) are from statistical fit results only.
c
R-factor = Σ(data-fit)2 /Σ(data)2 -- normalized sum of squared residuals of the fit.
d
Reduced χ2 = R-factor / ( # of points - # of variables) -- goodness of fit parameter accounting for the number of variables in the fit.