* Astronomy

Title: Chemistry, petrography, and mineralogy of the Tonk CI chondrite: Preliminary results
Authors: Endress, M.; Spettel, B.; Bischoff, A.

Chemically, CI chondrites are considered to be the most primitive material available for meteoritic studies; however, CI chondrites are highly brecciated and altered as well. A study of two thin sections (2 x 2 mm each) and a bulk sample of Tonk is reported. Tonk has a very low degree of brecciation and mineralogically appears rather homogeneous at least on a millimeter scale. As reported from other CI chondrites, single grains or clusters of magnetites are homogeneously distributed throughout the studied sections and very often associated with small Ca-phosphate grains. Sulfides (pyrrhotite) are much less abundant in Tonk compared to other CIs, forming either laths up to 100 microns long or hexagonal euhedral crystals. Carbonates are rare. We did not observe carbonate fragments like those previously reported in Ivuna and Orgueil. Calcium sulfates occurring as vein fillings are less abundant in Tonk than in other CIs.

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