GROSNAJA

A shower of stones fell after sonic booms at 7:00 P.M. in Grosnaja, Mekensk, USSR. Only one stone of about 3.5 kg was recovered, the remainder falling into the river Terek. It has been shocked to stage S3. The CV3 group was subdivided into the following three subgroups (McSween, 1977; Weisberg et al., 1997):

1. Reduced subgroup including Arch, Efremovka, Leoville, Vigarano, and QUE93429
2. Oxidized-Allende subgroup including Allende, Axtell, Tibooburra, and ALH84028
3. Oxidized-Bali subgroup including Bali, Kaba, Grosnaja, and Mokoia.

The oxidized-Allende and reduced subgroups are separated on the basis of metal abundance and Ni content of sulfide (Howard et al., 2010). The previously used discriminator, magnetite abundance, has been shown to overlap between oxidized and reduced subgroups. The oxidized-Bali subgroup has a higher degree of aqueous alteration than oxidized-Allende (for more mineralogical relationships, see Appendix I, Carbonaceous Chondrites).

*A recent study was undertaken by Bonal et al. (2004, 2006) to refine the subtypes of several CV3 chondrites. They utilized several methods to obtain their data, including Raman spectrometry of organic material, a petrologic study of Fe zoning in olivine phenocrysts, presolar grain abundance, and a noble gas study. These methods are in contrast to that of TL sensitivity data of feldspar which is typically used to determine subtypes of ordinary chondrites, and which was previously applied to the CV3 chondrites. They suggest that TL sensitivity data is not applicable to aqueously altered carbonaceous chondrites because of loss of feldspars through dissolution, leading to an underestimate of the petrologic subtypes. They have redefined the petrologic subtypes of the common CV3 members as follows:

	Raman	TL
Allende	>3.6	3.2
Axtell	>3.6	3.0
Grosnaja	~3.6	3.3
Mokoia	~3.6	3.2
Bali	>3.6	3.0
Efremovka	3.1-3.4	3.2
Vigarano	3.1-3.4	3.3
Leoville	3.1-3.4	3.0
Kaba	3.1	3.0

These differences in petrologic subtype are explained by Greenwood et al. (2009) in their study of CV and CK chondrite relationships. They assert that there is a decoupling between the silicate and organic components with respect to measurements involving thermal metamorphism.

The finding of Allende-like oxidized lithologies in the reduced Vigarano breccia, as well as in the Bali-like oxidized member Mokoia, indicates that all CV3 subgroups came from a common heterogeneous asteroid. The Bali-like matrix mineralogy was formed by one or more mechanisms; in particular, asteroidal aqueous alteration of material similar to that of the primitive CV3 reduced subgroup at temperatures below 300°C, or re-condensation of vaporized, pre-accretionary, chondritic-rich dust.

The Bali-like mineralogy of Grosnaja includes the phyllosilicates saponite and sodium phlogopite replacing Ca-rich minerals in chondrules and CAIs. It is unique within its group for containing serpentine and chlorite group phyllosilicates, indicative of higher than normal temperatures during alteration. Other secondary minerals present include magnetite, fayalite, andradite, and Ca–Fe-rich pyroxenes. In the Allende-like lithologies, present in all CV3 subgroups, virtually no phyllosilicate or fayalite is found in the chondrules or CAIs. Instead, nepheline, sodalite, fayalitic olivine, and Ca–Fe-rich pyroxenes are found indicating a higher temperature of alteration than that experienced in the Bali-like lithology on the CV parent asteroid.

Reflectance spectra have identified an asteroidal analog for the Bali-like meteorite Mokoia—the K-type asteroid 599 Luisa. Luisa is located near the 5:2 resonance at ~2.8 AU, supplying fragments into Earth-crossing orbits on short timescales. On the other hand, the ~39 km diameter, C-type asteroid 495 Eulalia was found to have spectral characteristics very similar to Grosnaja, including a "featureless" spectrum, a slight negative slope, and a virtually identical albedo (Fieber-Beyer et al., 2008). Moreover, Eulalia is located at the 3:1 Kirkwood gap (2.487 AU) and is predicted to rapidly deliver almost half of its ejected material to Earth crossing orbits; the timing is consistent with the 1.7 m.y. CRE age of Grosnaja. The above specimen of Grosnaja is a 1.5 g partial slice cut from a 20.5 g specimen formerly in the Natural History Museum, Humboldt University, Berlin.

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