A single large pallasite mass weighing of 17.7 kg was found ~80 km northeast of Mont Tourniat, Tiris Zemmour, Mauritania. The pallasite was subsequently sold to D. Pitt, and a type specimen of 66 g was submitted to the University of New Mexico (C. Agee, M. Spilde, and K. Ziegler) for analyses and classification. Mont Tourniat 001 was approved as an ungrouped pallasite in August 2023.
The Mont Tourniat 001 (MtT 001) pallasite is composed of partially rounded to angular, greeen to orange olivines (<40 vol%) embedded in an FeNi-metal host (~60 vol%), together with ubiquitous farringtonite (a phosphate first found in the Springwater pallasite) rimming olivine grains. Minor phases present include orthopyroxene, troilite, chromite, and schreibersite. Oxygen isotope values for four samples of MtT 001 plot on an extension of the main-group pallasite trend, but with somewhat higher δ18O values; therefore, MtT 001 occupies a unique O-isotopic space distinct from all other known pallasites (see diagram below).
Oxygen Isotope Diagram for Mont Tourniat 001
Diagram from MetBull 112
Based on all of the data gathered so far, it could be concluded that the pallasites in our collections represent at least thirteen separate parent bodies: (1a) main-group high-Δ17O; (1b) main-group low-Δ17O; (2) Eagle Station group; (3) Milton; (4) Vermillion + Y-8451 + Khatgal; (5) Zinder + NWA 1911; (6) Choteau; (7) NWA 10019 ± Bordj Badji Mokhtar 001; (8) LoV 263; 9) Hassi el Biod 002; (10) Lieksa; (11) Mont Tourniat 001; (12) Gyarub Zangbo; (13) NWA 16734. In addition, several pallasites with anomalous silicates (e.g., Springwater) and anomalous metal (e.g., Glorieta Mountain) could possibly increase the number of unique parent bodies. Proposed scenarios for pallasite formation can be found on the Imilac page. The specimen of Mont Tourniat 001 shown above is a 56.2 g partial slice, with excellent video-photography from T. Spinnato.
