La Posa Plain        33°49’56.35"N, 114°15’53.03"W

Arizona, United States

Confirmed fall: 2023 Dec 28

Classification: Ordinary chondrite (LL3-6)

History: (R. Matson, W. Cooke, M. Hankey, S. Clary, T. Scott) At 7:40:37 p.m. MST on 28 December 2023 a bright meteor traveled NE to SW across western Arizona recorded by two NASA/ASGARD all-sky cameras and rooftop cameras in Arizona City and Kingman, AZ, Laughlin, NV, and Lake Elsinore, CA. This fireball was widely seen across the southwestern US, with ~100 reports to the International Meteor Organization (IMO) fireball network - event #8283-2023. Witnesses in Fortuna Foothills and Scottsdale, AZ, reported hearing a sonic boom. First alerted of the fireball the following morning by an email from NASA/ASGARD (W. Cooke), R. Matson analyzed NASA’s triangulated trajectory as well as upper atmospheric wind data from radiosondes launched from Las Vegas and Flagstaff <3 hours prior to the fall. Matson found two signatures of falling meteorites in the Yuma station (KYUX) NEXRAD Doppler radar data consistent with the location and timing of NASA’s terminus after accounting for wind drift. The first appearance of falling meteorites is at 02:43:47 UTC at an altitude of 5.1 km (1.36° Yuma radar sweep elevation angle) 3 min 10 s after the fall, and the second at 2:45:09 UTC at an altitude of 2.9 km (0.53° Yuma elevation angle), 1.4 km ESE of the first signature. Matson adjusted NASA’s computed terminus location by a few km until the radar locations coincided with those of dark flight modeling and generated an estimated strewn field map assuming a chondritic meteoroid density. S. Clary and T. Scott arrived at this predicted location ~20 km N of Quartzsite, AZ, on December 30. The first stone was found by Sonny Clary midday on January 1, 2024: this was a 25.5 g fully fusion-crusted stone found in the La Posa Plain east of the Dome Rock Mountains in La Paz County, Arizona at 33° 49’ 56.35” N, 114° 15’ 53.03” W. Later the same day, Terry Scott found a 70.5 g stone at 33° 49’ 32.99” N, 114° 16’ 03.68” W. Meteorites were recovered on January 4, by Clary (189.3 g) at 33° 49’ 54.24” N, 114° 18’ 09.46” W and on January 6 a 96.96 g stone was found by R. Matson at 33° 49’ 48.50” N, 114° 16’ 52.70” W. Three further stones were found 24 g (Joe Franske) at 33°49’36.43”N, 114°15’52.23”W, 34.4 g (Mike Hankey) at 33°49’41.86”N, 114°16’15.81”W, and 123.8 g (Elizabeth Vieira) at 33°50’34.36"N, 114°17’10.47"W. Total known weight to date is 564.5 g.

Physical characteristics: The stones have thick brownish-black and shiny fusion crust. Interior of the stones is dominantly white to light gray, mottled and brecciated, with scattered large sulfides to 3 mm. The stones are friable and highly fractured.

Petrography: (L. Garvie, A. Wittmann, D. Schrader, ASU) The petrography is described from two 1” polished mounts containing 1.7 cm2 slices from the 189.3 g stone. The stone is a breccia with a fresh, 150 µm vesicular fusion crust. The breccia clasts have a wide range of textures from granular, to porphyritic, to poikilitic, to cataclastic, and interspersed with mineral fragments of >100 µm olivine, pyroxene, feldspar, iron sulfide, and Ni-rich Fe metal. The clasts with granular and porphyritic textures contain large, >100 µm, abundant regions of feldspar. No clast types dominate in the sections studied and the boundaries between the different clast types are difficult to identify. Clasts with granular and porphyritic texture show well-developed 120° grain junctions. Most of the minerals studied are equilibrated. However, the section contains a 150 × 600 µm clast dominated by euhedral, <20 µm, grains of FeO-zoned olivine with FeO-poor cores. A few grains have FeO-rich cores that are cloaked by FeO-poor olivine, which is further enclosed in an FeO-rich rim. A few clasts contain unequilibrated pyroxene. A few chondrules are recognized, such as two PO chondrules with equilibrated olivine (one is 2.9 mm and another is 600 µm), and a hard-to-identify and strongly recrystallized 900 µm barred olivine-pyroxene chondrule. The chondrules are interspersed with the range of petrographic types. Troilite is polycrystalline and shows a range of sizes and textures depending on its petrographic setting from small melt spheres to mm-sized masses. It is typically anhedral and blocky though many grains show a fizzed texture. Troilite is locally intergrown with pentlandite, and is more abundant than Ni-rich Fe metal. Kamacite is relatively rare occurring as <100 µm grains. Accessory minerals include chlorine-free and chlorine-bearing phosphates, chromite, ilmenite, silica, and copper. Sparse shock melt veins up to 20 µm wide are annealed. In addition, the section contains 12 coarse-grained clasts to 2000 µm dominated by albitic feldspar/K-feldspar/Na-Al-bearing silica and coarse-grained exsolved pigeonite (clinopyroxene lamellae within orthopyroxene host, and vice versa).

Geochemistry: Olivine – Excluding the one type 3 clast Fa_30.51±1.29, range Fa_23.37-32.19, FeO/MnO= 61.41±3.68, n=18; The range for the type 3 clast is Fa_18.4–30.2 and the Fe-rich rim contains 0.21 wt% Al₂O₃, 0.15 wt% CaO, 0.34 wt% Cr₂O₃, and 0.13 wt% NiO. Low-Ca pyroxene – Fs_25.04±1.12Wo_2.52±0.78, FeO/MnO=39.00±3.58, n=12; High Ca pyroxene – Fs_10.42Wo_44.01, n=1. Kamacite: Fe90.33±0.96Ni4.84±0.76Co4.72±0.94 (n=19) [wt%]; High-Ni metal: Fe46.14±11.22Ni50.93±10.74Co1.82±0.56, range: Fe 34.7±62.7, Ni 34.9±61.6, and Co 0.8±2.5 (n=14) [wt%]. Pentlandite: Fe47.04±1.15Ni18.17±0.50Co1.07±0.87S33.22±0.19, range: Fe 44.8±48.2, Ni 17.4±19.0, Co 0.5±2.9 (n=8) [wt%].

Classification: Ordinary chondrite with Fa and Fs values, and Co in kamacite consistent with an LL chondrite. The stone contains regions that are petrologic grade 3, a few well-developed but equilibrated chondrules consistent with petrologic grade 4. A few chondrules are also present that are hard to recognize, recrystallized, and largely integrated into the matrix consistent with petrologic grade 6. Many of the clasts and regions are highly recrystallized with a granular-porphyritic texture with well-developed 120° grain junctions. Overall, this stone contains regions consistent with petrologic grades 3 to 6.

Specimens: 21.26 g at ASU.