Black Silver Mine        33°17'50.82"N, 113°18'11.45"W

Arizona, United States     Confirmed fall: 2024 Apr 16

Classification: Carbonaceous chondrite (CK6)

History: (P. Jenniskens, D. Vida, N. Moskovitz, M. Fries, R. Matson, M. Hankey) At 7:59 pm MST on 16 April 2024 (02:59:27 UTC on 17 April 2024), a bright meteor was widely observed across the southwestern US, with 127 reports posted to the American Meteor Society fireball website (event#1981-2024). Tentative NEXRAD Doppler radar data did not line up well with distant NASA/ASGARD video observations. LO-CAMS and Global Meteor Network cameras in Prescott Valley, Sedona, and Flagstaff captured the beginning part of the fireball in greater detail (N. Moskovitz) but offered only a narrow range of perspectives. The event was also recorded by two AllSky7 stations that recorded the endpoint which showed good agreement with the radar data. K. Gosiger posted video security camera footage of the fireball from Phoenix and provided the original video upon request. That data was combined to calculate a trajectory (D. Vida), suggesting that the Doppler radar reflections originated from this meteor (M. Fries). Orbital calculations are consistent with an origin from the outer asteroid belt at a relatively high inclination (a = 2.75 AU, i = 14.4 °, q = 1.0015 AU). Based on this orbit alone, a CO/CV/CK type carbonaceous chondrite originating in the Eos asteroid family was expected to have fallen (See review by Jenniskens & Devillepoix, 2025). The predicted strewnfield was calculated by P. Jenniskens, D. Vida, M. Fries, and R. Matson. Search efforts were organized by Lowell Observatory and several meteorite hunters, but no finds were made, in part because of the remoteness of the location and extreme summer heat. Hunting resumed in February 2025 guided by updated strewnfield calculations of R. Matson and M. Hankey. On 11 February 2025, Steve Arnold found a fresh, fusion-crusted 88 g chondrite near Black Silver Mine in Maricopa County, Arizona. The find location overlaps the predicted fall location for this mass. A further eight stones were subsequently found for a total mass of 456.4 g (Table 1). Several more stones are reported to have since been recovered, though their masses and coordinates were not provided. All the stones recovered to date were found in an elliptical area measuring 1.6 × 0.35 km that overlaps the calculated strewnfield.

Physical characteristics: The stones are blocky to angular and lack signs of weathering. Most show two types of fusion crust - primary with thick crust and broad regmaglypts, and secondary with thinner crust coating a hackly fracture surface. The stones are exceptionally friable and crumble easily even while cutting. The interior is gray and studded with a few recognizable chondrules to 3 mm. One slice shows a recognizable 2 cm lighter-colored clast. Sulfides are visible in the cut and polished surfaces, but metal is not.

Petrography: (L. Garvie, A. Wittmann, ASU) Powder X-ray diffraction pattern of the bulk meteorite is dominated by reflections for olivine, magnetite, felspar, pentlandite, pyrrhotite, and minor pyrite. The petrographic description is based on a 1.2 × 1 cm slice in a 1" polished round section. Optical and BSE imaging shows a recrystallized texture with several coarsely crystallized chondrules and one 2 mm BO chondrule with an igneous rim. The majority of the chondrules are PO and coarsely crystalline with grains to 100 µm. Augite and orthopyroxene are dispersed as anhedral grains to 90 µm. Plagioclase occurs as grains and aggregates to 750 µm. Many of the grains have an overall euhedral lath morphology but are intensely poikilitic, and large grains have a skeletal appearance. Plagioclase compositions vary widely from An35.7 to An84.0, even within the same grain. Chlorine-rich Ca phosphates occur as grains <1 to 50 µm and are strongly associated with sulfide-magnetite-rich regions. Magnetite is abundant and occurs as rounded grains 50 to 300 µm and as abundant <50 µm grains in chondrules and less commonly in the recrystallized matrix. Element maps and BSE images show that the magnetite in the nodules and larger grains has an abundance of Ti-rich exsolution lamellae. These lamellae vary from <1 to 5 µm thick and to 100 µm long. Sulfides include pyrrhotite, pentlandite, pyrite, and chalcopyrite. Larger grains occur as myrmekitic intergrowths of pyrite and pentlandite. Chalcopyrite is rare and occurs as <50 μm grains associated with the myrmekitic intergrowths of pyrite and pentlandite. Noble metal-rich phases dominated by various proportions of Ru, Os, Ir, and Pt occur as sulfides, arsenides, and tellurides. Most grains are ~ 1 µm or smaller, though one 7.5 × 4 µm is dominated by Ir-Pt-As. High-resolution SEM images show significant porosity between the mineral grains and individual silicate grains are intensely porous. The BSE images and element maps were used to estimate the mineral proportions and porosity (areal%, estimated error ±10%): 57.1 - olivine, 16.8 - porosity, 10.3 - feldspar, 3.7 - sulfides, 3.2 - pyroxene, 3.5 - magnetite, 0.6 - phosphate.