Melt inclusions in igneous minerals can provide constraints on magma compositions, especially for planetary samples where mass is severely limited. Small inclusions (<15 lm diameter) are more abundant than large ones, but have been used little from concern that they did not entrap average magma, but are rich in melt of a diffusional layer against the host mineral. We compared bulk compositions and calculated original compositions of small and large melt inclusions in the Martian basalt meteorite (shergottite) Tissint. Small and large melt inclusions are consistent with the same line of igneous differentiation, have the same abundance ratios for incompatible elements (P, Ti, Al, K, Na), and are consistent with derivation from the bulk composition of Tissint (inferred to represent its parent melt composition). For Tissint, then, small melt inclusions show no evidence of entrapping diffusional boundary layers, and appear to have entrapped bulk magma. Thus, its small inclusions can be as useful as larger ones; this may be so for other planetary samples, and thus provides an additional tool for investigating planetary magmas.

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A partially serpentinized peridotite from the Josephine ophiolite has been studied in detail in order to characterize the chemical processes of its serpentinization. The original rock was harzburgite, and its olivine and orthopyroxene are partially replaced by veins and patches of lizardite serpentine and magnetite; brucite and talc are completely absent from the serpentinite, regardless of whether the precursor mineral was olivine or pyroxene. Petrographic and mineral-chemical data suggest at least two phases of serpentinization. Incipient serpentinization produced lizardite and magnetite veinlets, from preferential dissolution of orthopyroxene, and/or infiltration of a silica-rich fluid. No talc or brucite was produced, which suggests this serpentinization happened in a chemically open system. Later serpentinization was from a fluid closer to Fe-Mg-Si chemical equilibrium with the harzburgite, which should in theory favor formation of a brucite-bearing serpentinite. Brucite is absent from late serpentine veins, but they have some porosity which could represent former brucite that was dissolved out or was reacted out after serpentinization. Isocon modeling suggests that Si, Fe, and K were added during serpentinization and that Ca was lost; i.e., the serpentinization was not isochemical (except for H 2 O). Results of petrographic observations, thermodynamic modeling, and mass balance calculations were used to constrain the reactions for global serpentinization of the studied sample. These reactions indicate that water with a concentration of H 2 up to two times that of deep sea vent fluids may have been produced during the serpentinization of the Josephine peridotite, which could then have been a potential host for significant biomass.

Clast 100 in regolith breccia 15295 could be a key to resolving the relationship(s) between mare basalts and lunar picritic glasses. The clast is basaltic, with texture, mineralogy, mineral compositions, and calculated bulk composition suggesting that it crystallized in a thick lava flow or shallow intrusive body from a very‐low‐titanium (VLT) basaltic magma. The estimated bulk composition of clast 15295,100 is primitive (i.e., magnesian) compared to those of known VLT basalts, and is very close to those of VLT picritic green glasses, especially the Apollo 14 A green glass. From these similarities, we infer that clast 15295,100 is a crystalline product of a picritic magma similar to the Apollo 14 A glass. Clementine and M3 remotely sensed data of the lunar surface were used to find areas that have chemical compositions consistent with those of clast 15295,100, not only near the Apollo 15 site, but in a broad region surrounding the site. Two regions are consistent with clast's 15295,100 compositional data. The larger region is in southern Mare Imbrium, and a smaller region is in the eastern half of Sinus Aestuum. These locations should be considered as candidates for future missions focusing on sample science.