Petrographic and oxygen-isotopic study of refractory forsterites from R-chondrite Dar al Gani 013 (R3.5–6), unequilibrated ordinary and carbonaceous chondrites

Chondrites and Their Components

“…However, Jones et al that these objects were chondrules, that relict forsterites from such objects were present in other type I chondrules, and that refractory 16 O-rich forsterites were primitive nebular components. Pack et al (2004Pack et al ( , 2005 found <0.01-0.4 vol.% luminescent refractory forsterites in a variety of ordinary, carbonaceous, and R chondrites and found no difference in their chemical and isotopic compositions. Highly refractory forsterites with >0.6 wt% CaO and <0.5 wt% FeO are enriched in 16 O with D 17 O between À4 and À10%, whereas moderately refractory and nonrefractory olivines range between À5 and þ2%.…”

“…The oxygen isotopic and chemical compositions of the refractory forsterites lie beyond those at the FeO-poor end of the sequence defined by olivinerich, FeO-poor type IA chondrules and pyroxene-rich type IB chondrules (see Jones, 1994; Section 1.2.5.6.1). Melt inclusions in refractory forsterites are not in equilibrium with the olivine hosts -either because forsterite crystallized outside its stability field (McSween, 1977b) or because the melt reacted more readily with nebular gas than the crystallizing solids (Pack et al, 2004(Pack et al, , 2005Varela et al, 2005).…”

An experimental study on the hydrothermal preparation of tochilinite nanotubes and tochilinite–serpentine-intergrowth nanotubes from metal particles

“…However, systematic studies on various chondrites seem to suggest that highly reducing and high-temperature environments can exist locally in the solar nebula (Krot et al, 2000;Pack et al, 2004Pack et al, , 2005. Based on the framework of a recent model (or similar models) on chondrule and refractory inclusion formation (Shu et al, 1996Gounelle et al, 2001), one possible site for such highly reducing and high-temperature environments is the inner nebula near the protosun (Rai et al, 2005).…”

Re-examining the role of chondrules in producing the elemental fractionations in chondrites

“…Whether these forsterites formed in chondrules or earlier via condensation remains debated (e.g., Jones et al 2000;Pack et al 2004). If the fortserites are refractory condensates, they should have been accompanied by other refractory, presumably Al-rich, material.…”

“…If the fortserites are refractory condensates, they should have been accompanied by other refractory, presumably Al-rich, material. However, the low abundance of these forsterites (≤0.35 vol%: Pack et al 2004) means that even if they were accompanied by refractory material this would not significantly affect the matrix compositions. Except for the CVs, the positions of the CC matrix compositions in Fig.…”