Table 1: Astronomical and GEMS Composition Data.
  O/Sia Mg/Si$\sp{a}$ S/Si$\sp{a}$ Fe/Si$\sp{a}$ Isotopic composition Reference
Solar   1.01 0.52 0.9    Anders & Ebihara (1982)
Diffuse ISM   1 <0.12 0.9    Sofia (2004)
Average (200 GEMS) NRb 0.6 0.31 0.54    Keller & Messenger (2004)
Average (42 GEMS) NS ($+33\%$)c,  d 0.65 0.26 0.44    Ishii et al. (2008)
Anomalous GEMS            
GEMS 1 S ($-1.3\%$)e 0.75 0.31 1.3 $\delta\sp{18}$O ($\permil$) $+238\pm12$ isotopes:  Floss et al. (2006)
  S ($-9.7\%$)$\sp{e}$ 1.1 0.26 0.44 $\delta\sp{18}$O ($\permil$) $+238\pm12$ and Mg/Si: this work
GEMS 2 S 0.72 0.19 0.48 $\delta\sp{17}$O ($\permil$) $+523\pm85$ bulk GEMS isotopic compositions:
  $^{\prime\prime}$ $^{\prime\prime}$ $^{\prime\prime}$ $^{\prime\prime}$ $\delta\sp{18}$O ($\permil$) $-100\pm37$  Keller & Messenger (2007b)
GEMS 3 $^{\prime\prime}$ 1.2 0.19 0.43 $\delta\sp{18}$O ($\permil$) $+80\pm20$ $^{\prime\prime}$
  $^{\prime\prime}$ $^{\prime\prime}$ $^{\prime\prime}$ $^{\prime\prime}$ $\delta\sp{18}$O ($\permil$) $+145\pm30$ subregion of GEMS 3 above
GEMS 4 $^{\prime\prime}$ 0.37 0.26 0.47 $\delta\sp{18}$O ($\permil$) $-15\pm55$  Keller & Messenger (2008)
  $^{\prime\prime}$ $^{\prime\prime}$ $^{\prime\prime}$ $^{\prime\prime}$ $\delta\sp{17}$O ($\permil$) $+1220\pm260$ $^{\prime\prime}$
a Typically <$5\%$ analytical uncertainty. b NR = not reported. c NS = non-stoichiometric (average 33% excess O over stoichiometry). d Stoichiometry calculated by assigning O as MgO, SiO$\sb2$, Al$\sb2$O$\sb3$, CaO and S, Fe and Ni as sulfides and metal. e S = stoichiometric (within analytical uncertainty of $\pm $$10 \%$).

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