‘Kati Thanda (Lake Eyre South)’ fall officially registered as MURRILI
Murrili is officially registered in the Meteoritical Bulletin
“Murrili 29.26089°S, 137.53765°E
South Australia, Australia
Confirmed fall: 2015 Nov 27
Classification: Ordinary chondrite (H5)
History: The Murrili fireball was imaged by observatories of the Desert Fireball Network, and witnessed by local people at William Creek and Maree, as it blazed through the skies of South Australia around 9:15 pm on November 27, 2015. The object encountered the Earth close to its perihelion point, entering the atmosphere at 13.7 km/s. The object stopped ablating at an altitude of 18.32 km over Kati Thanda-Lake Eyre South. Its darkflight and fall position were modelled using a WRF climate model. An initial aerial search (2 weeks after the fall) revealed a small crater-like impact in the surface of the salt lake. The Arabana people are the traditional custodians of this land. Just after Christmas, with their permission and help – two Arabana men assisted with the search – the ground-based search team set out to collect the rock before rain erased evidence of the fall. On New Year’s Eve, a second aerial reconnaissance pinpointed the fall site. After some digging, the meteorite was pulled up through the salt-rich clay mud of the lake. It was recovered 218 m from the calculated fall line. The meteorite had punched a cylindrical hole through the mud and came to rest 43 cm below the surface.
Physical characteristics: Murrili fell as a single stone with a mass of 1.68 kg measuring approximately 13 × 7 × 6 cm. The mass was originally heart shaped. It is entirely covered with a matte looking fusion crust, aside from one small broken corner revealing a lighter gray interior. Two smaller wedges were cut from the mass for study. The cut surface shows extensive alteration with rusty staining heterogeneously distributed. The alteration does not affect the entire rock, there are areas that preserve the unaltered nature of the meteorite.
Petrography is based on investigations of a small polished thick section, which samples both the altered and unaltered materials in the sample. The overall texture is typical of ordinary chondrites having some chondrules (barred olivine, the remnants of porphyritic olivine, and possible radiating pyroxene) with distinct outlines, as well as large single mineral crystal clasts. Murrili contains olivine, orthopyroxene, plagioclase, metal and sulfide. Phosphate and chromite also occur in minor abundances. Metal and sulfide are randomly distributed throughout the sample. Some metal grains are altered on the edges, but the majority of metal grains are clean. There are fine-grained intergrowths of chromite-plagioclase.
Geochemistry: Olivine composition ranges from Fa18.5 to Fa20.4 (Fa18.8±0.5, n=15). Orthopyroxene ranges from Fs16.1Wo1.8 to Fs16.9W1.1 (Fs16.4±0.3Wo1.1±0.3, n=8). Chromite compositions range from Cr/Cr+Al = 0.850 to 0.868 (n=7); and Fe/Fe+Mg = 0.843 to 0.860.
Classification: The above compositions are consistent with classification at a type H ordinary chondrite. The texture, along with the Wo composition of OPX (Scott et al. 1986) and the chromite composition, indicates a petrologic type of 5.
Specimens: Main Mass is also type specimen at SAM. Two smaller pieces (137.2 g and 86.9 g) plus a cut slab (38.6 g) as well as one polished thick section are held at CUWA with the Desert Fireball Network team.