K3.6, K chondrite grouplet
Fell June 4, 1890
12° 23' N., 78° 31' E.
After sonic booms were heard, two stones were recovered in Tamilnadu, Salem, Kakangari, India. One stone was broken into pieces while the other, weighing 347 g, was preserved. Most of this meteorite is accounted for in only four institutions, the above specimen being obtained through the Natural History Museum in London by an American meteorite dealer.
Kakangari is a type 3.6 chondrite that belongs to none of the known chondrite groups, but has some characteristics in common with both ordinary and carbonaceous chondrite groups. It forms a duo with LEW 87232 (23 g), while a previously considered genetic relationship with Lea County 002 is no longer thought to be reasonable in light of significant differences in matrix abundances, chondrule sizes, and CAIs; instead, Lea County 002 is mineralogically and isotopically more similar to the CR chondrite group.
The Kakangari grouplet has unique petrologic and O-isotopic characteristics that distinguish it from other chondrite groups, including the following:
an oxidation state between H and E chondrites
a matrix unlike other chondrite groups (enstatite-rich and compositionally similar to the chondrules)
a high matrix abundance (30 vol%) similar to carbonaceous chondrites
a high metal abundance similar to H group ordinary chondrites
a high troilite abundance (10.5 vol%) with depleted chalcophile element abundances, indicative of large-scale sulfurization
refractory lithophile and siderophile abundances similar to ordinary chondrites
chalcophile elements that plot close to R chondrites
whole-rock O isotopic compositions that plot near the CR chondrites
chondrule O isotopic compositions that plot with the E chondrites
Kakangari consists of about half chondrules and half chondrule fragments, all type-I, FeO-poor, just as in the case with EH3 chondrules, and they are FeNi–FeS-rich. In addition, refractory material in the form of irregularly shaped CAIs is present. The relative proportion of chondrule textural-types, predominantly porphyritic and non-porphyritic, is unlike that in other chondrite groups. However, the abundance of POP chondrules is most similar to that of ordinary chondrites. Some porphyritic chondrules contain large metal–sulfide intergrowths having ragged outlines, while others contain small metal–sulfide beads within olivines and groundmass. Most chondrules and fragments also have metal–sulfide rims, but some have fine-grained, igneous-textured silicate rims. The abundance of silicate rims in Kakangari is intermediate to that found in the CV and ordinary chondrites. Layered rims are found on some chondrules, implying that they have experienced at least three melting events with two accretionary episodes. Spongy troilite usually forms the final layer on chondrules and fragments.
The matrix mineralogy preserves the thermal history of Kakangari, revealing formation by high temperature annealing, without complete melting, of aggregates of ultrafine-grained material. This precursor material was likely a mixture of nebular and presolar dust. A period of rapid cooling has been proposed to explain the production of orthoenstatite and clinoenstatite in the matrix. Chondrules and matrix have similar compositions and experienced reduction at some point, with the chondrules being less reduced than matrix silicates. Kakangari chondrules probably formed from material similar to that from which the matrix was formed, but reached higher temperatures necessary for complete melting. Solar-wind-implanted He and Ne suggest a residence in a regolith, with the probability that it is a breccia. Aqueous alteration processes produced ferrihydrite and chlorapatite as replacements for kamacite.
While no FeO-rich chondrules are present in either Kakangari or E chondrites, FeO-rich silicates are present in both (Berlin et al., 2007). These silicates do show evidence for reduction processes; the E chondrites were reduced to a greater degree than Kakangari as demonstrated by the more Mg-rich chondrules and higher contents of Cr and Ti in the troilite of E chondrites. It was suggested that the FeO-rich silicates in both of these groups had a common precursor, despite their differences in degree of reduction. In a broader sense, the K chondrites have a combination of properties that do not fit the existing systematics of either the E, O, R, or C chondrites for which isotopic, chemical, and petrologic characteristics vary smoothly relative to their heliocentric distance of formation. For example, the chondrule/matrix ratio is negatively correlated to the oxidation state through the series E>H>L>LL>C3>CM2>CI1, but the K chondrites do not fit into this sequence. Redox analysis suggests that Kakangari contains a unique suite of chondrules (Berlin et al., 2007).
Generally, bulk chondrules in Kakangari plot along the terrestrial fractionation line (ave. olivine: Δ17O +0.2 ±0.6‰; ave. low-Ca pyroxene: –0.1 ±0.7‰), while the matrix olivine and low-Ca pyroxene grains have O-isotopic compositions that are slightly 16O-enriched (by 2.6‰); actually, the matrix grains are divided between a majority that are 16O-rich (Δ17O –23.5 ±2.9‰) and others that are 16O-poor (Δ17O –0.1 ±1.7‰). As indicated by the O-isotopic data, Kakangari chondrules and the 16O-poor matrix component likely formed from the same nebular reservoir (Nagashima et al., 2011).
A NanoSIMS study of Kakangari conducted by Floss and Stadermann (2009) revealed a single 13C-rich grain (equivalent to ~9 ppm) and only relatively low abundances of presolar silicate/oxide grains, as well as a complete lack of both anomalous O grains and amorphous silicates in its matrix. These findings suggest that Kakangari experienced secondary processing, probably on the parent body, and thus cannot be considered a primitive meteorite.
The fusion crust of Kakangari is dull and dark brown, and exhibits a close textured, locally ribbed and netted texture (S. Ghosh and A. Dube, 1999). The photo shown above is a 1.15 g surface fragment of Kakangari with the fusion-crusted side shown beneath.
