A single 264 g meteorite was found in Northwest Africa and subsequently purchased by M. Jost of Space Jewels Switzerland. A sample was sent for analysis and classification to the Museum für Naturkunde in Berlin, Germany (A. Greshake), and based on mineralogical analyses NWA 6047 was determined to be a rare unequilibrated CK3 chondrite.
This meteorite has a dark-brown, fine-grained matrix with large, well-defined chondrules, and its silicates preserve a wide compositional range, features which are indicative of a low degree of thermal metamorphism consistent with a classification of type 3. This carbonaceous chondrite exhibits an unusually high matrix to chondrule ratio with an almost complete lack of FeNi-metal. Minor phases include Ni-rich sulfides, Cr-bearing magnetite, and rare CAIs. It is unshocked to very weakly shocked (S2) and has experienced significant terrestrial weathering (W3).
Comparatively, the CK group has a high oxidation state which has resulted in a very low content of FeNi-metal and a correspondingly high content of magnetite and sulfides. The dispersion of these sub-µm- to µm-sized magnetite and sulfide (pentlandite) grains within vesicles of like size has caused pronounced silicate darkening in all metamorphic grades. In addition, CK chondrites generally have high matrix to chondrule ratios, with the matrix composing ~5070 vol%. Chaumard and Devouard (2016) reported a large range in chondrule abundances among CK chondrites in their study, which they attributed to re-equilibration during metamorphism.
Previous studies (e.g., Sanborn et al., 2014) have established that a coupled Δ17O vs. ε54Cr diagram is one of the best diagnostic tools for determining genetic relationships among meteorites. New Cr- and O-isotopic analyses were conducted by Yin et al. (2017) for two new equilibrated CK chondrites (NWA 7461 and NWA 7704) as well as for unequilibrated NWA 6047 and CV3 Allende. When combined with previous analyses, it was determined that CK chondrites have an average ε54Cr value of +0.66 (±0.06), while the CV chondrites have an average value of +0.88 (±0.06). The significantly higher ε54Cr (+1.23 [±0.09]) and the Δ17O values determined for NWA 6047 indicate that it could represent a unique parent body separate from that of CK, CV, and CO chondrites (see diagrams below).
Diagrams credit: Yin et al., 48th LPSC, #1771 (2017)
Chromium vs. Oxygen Isotope Plot
click on diagram for a magnified view
Diagram credit: Sanborn et al., 49th LPSC, #1780 (2018)
A petrographic and mineralogical study of NWA 6047 (and other CK3 meteorites) was conducted by Dunn and Gross (2017) to better resolve the group classification, CV vs. CK. They determined that the magnetite composition of NWA 6047 is consistent with that of CV chondrites with respect to Cr2O3, TiO2, NiO, MnO, and CaO abundances; however, the abundance of Al2O3 was found to be lower than that of CV chondrites. They also found that the Fa content in matrix olivine is most similar to CV chondrites, as are the minor element abundances with the exception of Cr2O3 (higher than in CV) and MnO (lower than in CV). In addition, the average Fa content of chondrules in NWA 6047 (Fa1.9) is very much lower compared to the FeO-rich chondrules of CK chondrites, but is similar to the chondrule Fa values of CV chondrites. With respect to petrographic observations, they found that the chondrule abundance in NWA 6047 (~30 vol%) is lower than that in CV chondrites (~40 vol%) but higher than that in CK chondrites (~22 vol%). Furthermore, CAIs are present in both NWA 6047 and CV chondrites, but are rare in CK chondrites. Based on the combined results of their analyses, Dunn and Gross (2017) suggest that NWA 6047 be reclassified as CV3ox.
The photo of NWA 6047 shown above is a 6.92 g slice measuring 5 cm across with a small portion of a CAI visible. The photos below show a nice slice of NWA 6047, in the collection of Stephan Kambach, and a photo of the main mass. The bottom image is an excellent petrographic thin section micrograph of NWA 6047 shown courtesy of Peter Marmet.
Photo courtesy of Stephan Kambach
Photos courtesy of Marc Jost
click on photo for a magnified view
Photo courtesy of Peter Marmet