Dishchii’bikoh Ts’iłsǫǫsé Tsee (Cibecue Star Stone) officially registered as witnessed fall (LL7, S3, W0)

Dishchii’bikoh has been officially registered as witnessed fall

Dishchii’bikoh is Apache for Cibecue. The meteorite’s full name is Dishchii’bikoh Ts’iłsǫǫsé Tsee ♫ (Cibecue Star Stone).

“Dishchii’bikoh 33°53’0.48″N, 110°38’8.20″W

Arizona, USA

Confirmed fall: 2 Jun 2016

Classification: Ordinary chondrite (LL7)

History: (D. Dunlap, M. Fries, R. Garcia, L. Garvie, M. Hankey, R. Matson, P. Mane, M. Miller, R. Ward) At 3:56:34 MST (10:56:34 UTC) on 2 June 2016, a bright fireball was widely observed throughout the southwestern US. The fireball was recorded in imagery from the NOAA NEXRAD weather radar network, on the KFSX radar in Flagstaff, Arizona. Radar reflections consistent with falling meteorite material were first recorded at 10:57:12 UTC at an altitude of 9.7 km above sea level (ASL). Two additional radar sweeps recorded the event, at 11:01:14 UTC (5.1 km ASL) and 11:02:30 UTC (5.1 km ASL). The mass of meteorites for these detections was estimated at 3.7 kg, 2.15 g, and 0.54 g respectively, using M. Fries’ dark-flight model Jörmungundr (v.42) and wind velocity data from a radiosonde launched from Flagstaff at 00:00 UTC. The fireball was also recorded on US Department of Defense orbital sensors, leading to a total radiated energy of 17.2 × 1010 J, with energy equivalent to 0.49 kiloton of TNT. The air-blast shockwave was recorded on the earthquake seismic network from the Payson-Strawberry station. Analysis of the Doppler radar data showed stones likely on the ground on the southwestern corner of the White Mountain Apache tribal (WMAT) lands. With the help of Jacob Moore (Assistant Vice-president of Tribal Relations, ASU), permission was granted by Ronnie Lupe, the WMAT Tribal Chairman, to enter the tribal lands and search for and collect meteorites. Laurence Garvie, Daniel Dunlap, and Prajkta Mane of ASU, and private meteorite hunters Robert Ward, Mike Miller, and Ruben Garcia searched for meteorites starting 22 June 2016. Robert Ward found the first stone, 0.93 g, at 33°53’19.7 N and 110°37’55.0’ W. A total of 15 fusion-crusted stones weighing from 0.9 to 28.6 g, for a total of 79.46 g, were found on 22 and 23 June, 2016. The stones were found along a 1.7 km transect, with a 10.16 g stone found at 33°53’0.48″N and 110°38’8.20″W near the center of the finds, though this location is likely at the small end of a large strewnfield that extends to the SW.

Physical characteristics: (L. Garvie, D. Dunlap, P. Mane, ASU; R. Ward, M. Miller, R. Garcia). Fifteen fusion-crusted stones for a total mass of 79.46 g. Fusion crust is dominantly shiny black, though on two stones it is brown, matte, and powdery. Five of the stones broke upon impact. Interiors are whitish gray, with uneven distribution of darker clasts to 5 mm, and troilite to 3 mm. Stones are dominantly soft with a sugary texture.

Petrography: (L. Garvie, ASU) Pieces of four stones were mounted in epoxy and polished. Sections show a breccia of clasts dominated by granoblastic textures in a cataclastic matrix. Granoblastic areas: areas with this texture occur as rounded clasts with a sharp boundary to the cataclastic material. No easily recognizable chondrules were visible, though one 200-μm-sized grain may be a remnant BO chondrule, and two rounded 500 μm-sized areas with finer-grained pyroxene than enclosing material may represent former PO chondrules. Silicates typically <400 μm. Feldspars coarse grained, commonly >50 μm, some grains to 300 μm. Troilite and taenite <400 μm across, rounded to subhedral. Troilite ~2 areal%, taenite ~1 areal% and trace kamacite. Troilite is single crystal and lacks shock lamellae. Native copper is sparse, to 30 μm. Accessory chromite to 200 μm. Cataclastic areas: Angular silicates to 200 μm. Troilite grains with feathery margins, though still single crystal and lacking shock lamellae. One section is traversed by several shock veins, with the sulfide dominantly fine-grained anastomosing network. Sulfide-rich clasts, to 2.5 mm, with FeS finely dispersed as small grains or as anastomosing network. Geochemistry: (L. Garvie ASU, P. Mane, UAz) Olivine, low-Ca pyroxene, and plagioclase dominate the sections. Microprobe results from the cataclastic and granoblastic regions are the same. Olivine Fa31.0±0.3, FeO/MnO=59.6±3.4, n=14; low Ca-pyroxene Fs25.0±0.3Wo1.8±0.3, FeO/MnO=35.6±2.0, n=9; high Ca-pyx Fs11.2Wo43.1, FeO/MnO=46.6, n=1; plagioclase Ab85.8±1.6An10.9±0.5, n=10; taenite - Ni 50.0±3.1 wt%, Co 1.9±0.2 wt%, Cu 0.18±0.06, n=10; kamacite - Ni 3.7±0.5 wt%, Co 11.8±0.7 wt%, n=10; chromite - Cr/(Cr+Al) = 0.85±0.01, Fe/(Fe+Al) = 0.79±0.03, n=10; and, phosphates dominated by apatites with F 1.1±0.3 wt% and Cl 4.4±0.3 wt%, n=7. Classification: Ordinary chondrite, LL7, S3, W0."