Q Pl -gases

Primarily because of their rather normal isotopic composition, it is generally assumed (but in no way certain) that Q-gases (and hence Q) are of local, possibly Solar System, origin, unlike the gases hosted by the presolar circumstellar phases being discussed further below. 

Within the Q component as operationally defined variations in composition have been observed, partly at least connected with metamorphic history (Huss et al. 1996 Busemann et al. 2000). The most clear-cut trend is the decrease of the abundance of Q gases with increasing metamorphic grade of the host meteorites, coupled with an increase in median release temperature (Huss et al. 1996). As far as isotopic compositions are 

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