Ksar Ghilane 022 Ungrouped Achondrite Meteorite End Cut, Achondrite-ung, 9.07g, Augite-Dominant Interior

Augite-rich igneous texture in a 9.07g end cut

This 9.07-gram end cut from Ksar Ghilane 022 exposes an interior dominated by coarse augite crystals that formed through differentiated melting processes. The slice reveals the mineral assemblage that distinguishes this ungrouped achondrite: predominantly equant augite grains averaging 1.5 millimeters across, interspersed with minor enstatite and accessory phases including chromium-bearing troilite, daubreelite, alabandite, and manganese-iron oxide. Secondary calcite veins crosscut the primary igneous texture.

The end cut format preserves one natural exterior surface while exposing a cross-section through the specimen's interior structure. The polished face allows direct observation of grain boundaries and the spatial relationships between augite, enstatite, and sulfide phases. This presentation makes the specimen particularly effective for examining the petrographic characteristics that place Ksar Ghilane 022 outside established achondrite classification schemes.

Mineral assemblage and crystallization history

The mineral chemistry recorded in the Meteoritical Bulletin confirms augite with ferrosilite content near 0.0 to 0.1 and wollastonite ranging from 39.4 to 42.3. Enstatite shows ferrosilite around 0.1 and wollastonite between 0.9 and 3.6. These compositions indicate crystallization from a magma that underwent significant fractionation, producing calcium-rich pyroxene as the dominant phase while retaining only minor orthopyroxene.

The accessory sulfide assemblage includes Cr-troilite, daubreelite, alabandite, and manganese-iron oxide, representing late-stage crystallization products. The presence of secondary calcite veins indicates post-crystallization alteration, likely during terrestrial weathering after the meteorite's fall to Earth. The combination of igneous minerals and terrestrial alteration features provides insight into both the specimen's formation environment and its history since arriving on our planet.

Scientific context

Ungrouped achondrites represent differentiated asteroidal material that cannot be assigned to known achondrite families. These meteorites formed through partial or complete melting of their parent bodies, producing igneous rocks with mineral assemblages distinct from both primitive chondrites and classified achondrite groups. Ksar Ghilane 022's augite-dominated composition, coupled with its specific pyroxene chemistry and accessory phases, sets it apart from eucrites, angrites, and other established achondrite classifications.

Its oxygen isotope composition falls in the field of the enstatite chondrites and aubrites, but its mineralogy does not match any established group, which is why the Meteoritical Bulletin classifies it as ungrouped. This isotopic signature, combined with the unusual mineral assemblage, indicates formation on a differentiated asteroid with a distinct evolutionary history. Each ungrouped achondrite potentially represents material from a different parent body, making these specimens critical for understanding the diversity of igneous processes that occurred across the early Solar System. Collectors interested in differentiated meteorites can explore our complete selection at Ungrouped Achondrites.

What the research reports

The Meteoritical Bulletin classifies Ksar Ghilane 022 as an ungrouped achondrite (Achondrite-ung), published in Meteoritical Bulletin 113 (2025). The writeup, by A. Irving and P. Carpenter, describes a rock made mostly (more than 90 percent by volume) of nearly iron-free augite, with minor enstatite and unusual sulfides, from a find in Tunisia in 2023 with a total recorded mass of 50 kg. The research below comes from the authors’ own samples and methods and is given here as the study states it.

Rider-Stokes et al. (2025): a Mercury analog, not a proven Mercury meteorite

B. G. Rider-Stokes, E. Branagan-Harris, K. Markus, J. F. Snape, S. L. Jackson, S. S. Russell, R. C. Greenwood, T. H. Burbine, M. J. Whitehouse, D. A. Rothery, L. F. White and M. M. Grady published Insights into pyroxene-dominated surfaces and implications for ongoing space exploration missions (Icarus, volume 441, article 116713, 2025). The lead author is at The Open University. The study examined Ksar Ghilane 022 alongside Northwest Africa 15915, which appears to be related. Both contain iron-free silicates and unusual sulfides such as oldhamite, have oxygen isotope compositions in the field of the enstatite chondrites and aubrites, show almost no spectral features in visible and near-infrared light, and have a mineralogy similar to what is expected for the surface of Mercury.

What the authors concluded. The paper does not claim these rocks came from Mercury. Its abstract states that “it is unlikely that the two meteorites are fragments of Mercury,” while suggesting they may be good analogs for Mercury’s surface on a regional scale, useful for comparison with data from the ESA and JAXA BepiColombo mission. News coverage in 2025 described them as possible Mercury meteorites. In an Open University news release, the lead author noted clear differences from Mercury, including infrared data, plagioclase content and age, while adding that a Mercurian origin cannot be ruled out.

Frequently asked questions

Is this meteorite authenticated? Ksar Ghilane 022 is officially classified in the Meteoritical Bulletin as Achondrite-ung. You can verify this classification at Meteoritical Bulletin Database. This specimen includes a certificate of authenticity from Treasure Coast Meteorite Co.

What does "ungrouped achondrite" mean? An ungrouped achondrite is a differentiated igneous meteorite that does not fit into any established achondrite classification scheme. The mineral assemblage, chemistry, and oxygen isotopes distinguish it from eucrites, diogenites, angrites, and other known groups, indicating a parent body not represented by any established group; a 2025 study found it closely related to Northwest Africa 15915.

What is included with this specimen? You receive the 9.07-gram end cut slice and a certificate of authenticity. No display stand is included with this specimen.

What are augite and enstatite? Augite and enstatite are both pyroxene minerals that form in igneous environments. Augite is a calcium-rich clinopyroxene that crystallizes at relatively high temperatures, while enstatite is a magnesium-rich orthopyroxene. The dominance of augite over enstatite in this specimen indicates the magma chemistry favored calcium-rich pyroxene during crystallization.

Why is the oxygen isotope composition significant? Oxygen isotope ratios act as a fingerprint for identifying parent bodies. Each asteroid or planetary body has a characteristic oxygen isotope signature that reflects conditions during its formation. Ksar Ghilane 022's oxygen isotopes fall in the field of the enstatite chondrites and aubrites. Combined with its unusual mineralogy, which matches no established group, this suggests a differentiated parent body that no established group samples. A 2025 study found it closely related to Northwest Africa 15915, probably from the same parent body.

Display and collection value

The 9.07-gram size provides substantial hand specimen presence while remaining accessible for collectors building comprehensive achondrite collections. The end cut format offers both an exterior surface and a polished cross-section, allowing examination of both weathering features and internal structure. The coarse grain size makes individual augite crystals easily visible, providing a clear demonstration of the igneous texture that characterizes differentiated asteroidal material.

Ungrouped achondrites hold particular significance for collectors focused on parent body diversity. While classified achondrites like eucrites and angrites are well-represented in collections, ungrouped specimens offer the opportunity to own material from asteroids not otherwise represented in meteorite collections. This specimen documents a distinct differentiation history, mineral chemistry, and oxygen isotope signature that together define a separate lineage among differentiated Solar System bodies.

Meteoritical Bulletin entry: Ksar Ghilane 022 | Classification: Achondrite-ung | Find, Tunisia, 2023