(troilite–metal nodule bearing)

standby for nwa 2646 photo
click on photo for a magnified view

Fell May 22, 2012
21° 16' 09" N., 78° 34' 49" E., main mass

In 2012, May 22 at approximately 2:30 P.M., a fireball accompanied by detonations was seen and heard by local residents as it streaked over the Akola and Nagpur districts of India, moving in a generally eastward direction. At the same time, the Broadband Seismic Observatory of the Geological Survey of India recorded a 2.1 magnitude seismic event lasting 90 seconds, which was centered 30 kms ENE of Akola. Several meteorite fragments were quickly recovered by residents in and around Katol.

Four fragments were recovered initially by residents at different locations, and these were documented by a team of geoscientists led by Binod Kumar: 1) the largest fragment, weighing 673.5 g, was found at Lakshmi Nagar by Nathoji Ramakrishna Charde; 2) a 74.4 g fragment was found near Khutamba road by Javed Razzak Shaikh after it penetrated the galvanized metal roof of a shed, damaging the concrete floor below; 3) a fragment was found at IUDP Layout by Govinda Muralidhar Mahajan that had penetrated 10 cm into the soil; and 4) a fragment was found at IUDP Layout towards Nagpur road by Pundlik Kashiram Shivarkar. It is now reported that more than 30 fragments have been recovered, having a combined weight of ~13 kg (Ghosh and Murty, 2014).

Extensive analyses of this unique meteorite were conducted at research facilities in both India (Geological Survey of India; Physical Research Laboratory; National Geophysical Research Institute) and America (Center for Meteorite Studies at Arizona State University; Institute of Meteoritics at University of New Mexico), eventually being published in the 2013 Meteoritical Bulletin #102 classified as an L6 chondrite.

An independent classification of Katol was published by Ghosh and Murty (Physical Research Laboratory, India) at the 45th LPSC, #1300 (2014). Here, Katol was classified as a shock-melted L6–7 ordinary chondrite, the first such breccia ever described. Although they report observing no discernable chondrules in the light-gray, recrystallized silicate matrix (primarily composed of olivine and low-Ca pyroxene), they did find rare microchondrules. Minor phases include plagioclase (mostly transformed to maskelynite), troilite, FeN-metal, high-Ca pyroxene, merrillite, and chromite. While specks of FeN-metal and troilite are ubiquitous throughout the meteorite, an ~2 cm-sized, shock-melted, multi-textured troilite–metal nodule was described as a shock-generated fragmental breccia.

The troilite–metal nodule is composed of a complex intergrowth of most of the same components present in the bulk meteorite, but with the addition of various high-pressure phases including wadsleyite and ringwoodite (Ray et al., 2014). These high-pressure phases correspond to shock pressures of at least 45 GPa (S5) and temperatures in the range of 900–1500°C. In addition, the presence of a complex network of sub-mm to µm-scale shear-stress-induced melt veins with interconnected metal-sulfide melt pockets, as well as silicate grains with planar deformation features, attests to a shock-heating event in which some localized shock pressures approached ~90 GPa (S6+). Based on microtextural evidence such as the quench-texture of the troilite–metal nodule, it was inferred by Ray et al. (2017) that the nodule was formed in a severe impact long after the chondritic host rock had become thermally metamorphosed to type 6–7, and that it was incorporated into the host rock during brecciation processes prior to ejection from the parent body.

Through measurements of the 60Co and 36Cl abundances, Murty et al. (2014) calculated the pre-atmospheric diameter of the Katol meteoroid to have been 1.7–3.4 m. Based on cosmogenic noble gas studies, they determined the CRE age to be 50 (±5) m.y. The specimen of Katol shown above is a 1.17 g partial slice.