(CM2.2; Rubin et al., 2007)
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Fell August 1, 2020
1° 53' 18.8" N., 98° 39' 39.6" E.
Around 4:40 P.M., several stones were seen and heard to fall in Setahi Nauli village, Kolang district in North Sumatra's Central Tapanuli Regency, on the Indonesian island of Sumatra. The largest stone weighing ~2.2 kg penetrated the metal roof overhanging the house of Josua Hutagalung and buried itself in the soil at a depth of ~15 cm. Mr. Hutagalung initially sold a few fragments that were removed from the stone, and thereafter he sold the remaining 1.843 kg main mass to three meteorite dealers (M. Lyon, R. Wesel, and J. Collins) who then sold it to collector J. Piatek. The total known weight of the Kolang fall is 2.55 kg. See the Karmaka Meteorites link at the bottom of the page for full details of the fall including numerous videos.
Kolang Main Mass In Situ
Kolang Main Mass with Adhering Soil
Photos credit: Josua Hutagalung, courtesy of Karmaka Meteorites
Samples were sent for analysis and classification to Arizona State University (L. Garvie) and the University of New Mexico (oxygen isotope analysis; K. Ziegler), and Kolang was determined to be a CM1/2 chondrite, the first of its kind to be recovered as a fall. The MetBull description of Kolang by L. Garvie states that Kolang is a breccia with clasts that exhibit significant variability in mineralogy, aqueous alteration phases, and abundance of chondules. This variability was also noted by Jenkins et al. (2021) with respect to the abundance and distribution of Ca, S, and metal among breccia clasts over the cm scale, which attests to open system aqueous alteration by fluids of varying composition. Jenkins et al. (2021) also found that the chondrules in Kolang have been significantly flattened (aspect ratio ≈ 1.5) in one or more impact events. Based on the consistency among chondrule azimuthal angles between the clasts, the impact(s) occurred after brecciation and lithification. Two predominant breccia clast types were recognized by L. Garvie, chondrule-rich and chondrule-poor, with a greenish-grey breccia clast present at a lower abundance. In one sample he identified a pinkish-colored CAI measuring 3 mm in size.
Modal abundances for Kolang obtained by King et al. (2021) are 82 vol% phyllosilicates, 8 vol% olivine, 5 vol% pyroxene, 3 vol% magnetite, 1 vol% Fe-sulfides, and 1 vol% calcite. In addition, King et al. (2021) employed thermogravimetric analysis to derive an estimate of the water abundance in Kolang of ~13 wt%. They also applied the aqueous alteration scale of Howard et al. (2015) to derive a phyllosilicate fraction (PSF) of 0.86, which defines a petrologic subtype of 1.3; this is equivalent to subtype 2.2 on the alteration scale of Rubin et al. (2007). It is noteworthy that a CM1 clast, sample ASU2147_C3c, was identified in Kolang (Schrader et al., 2021).
Organic matter in the form of polycyclic aromatic hydrocarbons (PAH) was studied by Lecasble et al. (2021) in Kolang and several other CM2 chondrites. It was determined to be present in Kolang at a higher concentration than in either Aquas Zarcas or Tarda, but maybe at a lower concentration than in Mukundpura.
Some carbonaceous chondrite groups, including the CM group, show a trend of decreasing Fe/S ratio of pyrrhotite with increasing aqueous alteration (Schrader et al., 2021 and references therein). A high degree of aqueous alteration under oxidizing conditions is evident in Kolang by its low Fe/S ratio of pyrrhotite of 0.893, with an average of 0.901 being typical for CM1/2 chondrites. In comparison, the CM1 clast ASU2147_C3c has a Fe/S ratio of pyrrhotite of 0.890. It is also recognized that subsequent heating of carbonaceous chondrites results in higher Fe/S ratios of pyrrhotite along with the formation of troilite (Schrader et al., 2021 and references therein). The O-isotope plots of seven clast samples are shown in the oxygen three-isotope diagram below, including two plots for each sample and excluding a metal- and chondrule-rich clast with disparate values; all of the plots fall within the field of CM chondrites.
Diagram adapted from MetBull 109
The specimen shown above is a 2.25 g fragment from the main mass of Kolang obtained from M. Lyon. A small portion of the specimen has fresh fusion crust with some adhering soil.
For additional information and videos about the Kolang meteorite fall, visit the excellent webpage by Karmaka Meteorites.