Chasseron        46°51.07’N, 6°32.32E

Vaud, Switzerland

Find: 1959

Classification: Pallasite (Main group)

History: Found by Mr. Reto Merlo, Grüningen, Switzerland, during a school excursion in summer 1959 while he was searching for firewood. The finder remembers having found the sample between the hotel and the summit of Chasseron (distance ~160 m). The finder glued the sample on a piece of wood and kept it until 2017. After reading about meteorites, he sent the sample to the NMBE (received May 9, 2017) from where it was transferred to UNIL.

Physical characteristics: Metallic sponge shape, only slightly rusted, fragment with embedded yellow-green forsterite (olivine) grains. Locally fresh-looking, shiny fusion crust on metal and olivine. 23.5 × 13 × 11 mm.

Petrography: Typical pallasitic texture. Forsterite (olivine) grains size is 8-2 mm. Droplet-like troilite grains up to 0.6 mm embedded in forsterite (olivine). Schreibersite rounded inclusions in Ni-rich iron up to 1.8 mm. Ni-rich iron weathering is relatively low in an outermost zone just 0.1 mm thick, consistent with weathering grade W1. Bulk density by immersion in isopropanol is 6.17 g/cm3. From density calculation, volume fraction of forsterite is 57% and volume fraction of Ni-rich iron is 43%.

Geochemistry: Forsterite (olivine): microprobed Fa_14.9±1.1 (range Fa_13.6-15.9), Fe/Mn (at.) 34± n=5. Two analyses of Ni-rich iron (variety kamacite) yielded: Ni 7.15±0.21 wt. % and Co 1.20±0.20 wt. %. One analysis of schreibersite (XRD checked) yielded the following formula (based on 4 apfu): (Fe_1.92Ni_0.97Co_0.03)_2.92P_1.08. Stoichiometric troilite crystals checked by XRD. One analysis of chromite (XRD checked) yielded the following formula (based on 4 oxygen atoms):(Fe_0.62Mg_0.35Mn_0.03)_1.00(Cr_1.65Al_0.31Fe_0.02V_0.02)_2.00O₄. Forsterite (olivine) oxygen isotopes (R. Greenwood, OU): δ¹⁷O 1.514±0.051, δ¹⁸O 3.239±0.094, Δ¹⁷O -0.170 (n=2). Cosmogenic radionuclides: (Å. Rosén, GeMSE): Gamma-spectrometry performed in May 2017 showed significant activities of ²⁶Al (10.8+2.5/-1.7 dpm/kg) and ⁴⁰K (17.6+9.3/-4.9 dpm/kg, probably a contamination). No short-lived cosmogenic isotopes were detected. A significant activity (17.0+2.1/-1.2 dpm/kg) of ¹³⁷Cs is present as terrestrial contamination, consistent with a first peak of nuclear bomb-produced ¹³⁷Cs in the years 1957-1959.

Classification: This is a main-group pallasite based on texture, mineralogy and mineral composition including oxygen isotopes. Low degree of weathering.

Specimens: 4.8446 g and one epoxy resin polished section with isolated olivine grains at UNIL; sample number 093320.