Ksar Ghilane 022 Ungrouped Achondrite Meteorite Slice, Achondrite-ung, 1.75g, Augite-Rich Matrix

Differentiated material from an unknown parent body

This 1.75g slice exposes a cross-section of augite-dominant matrix representing differentiated planetary crust that does not match any established achondrite group. The specimen preserves an equant crystal texture where individual augite grains average 1.5 mm across, creating a granular fabric visible throughout the slice. Minor enstatite appears interspersed among the pyroxene grains, alongside accessory phases including chromium-bearing troilite, daubreelite, alabandite, and manganese-iron oxide. Secondary calcite veining crosses portions of the matrix, recording post-formation aqueous alteration.

The slice format allows observation of the textural relationships between mineral phases and provides a representative sample of the meteorite's internal structure. Found in Tunisia in 2023, this specimen joined the small inventory of ungrouped achondrites that challenge existing classification frameworks.

Pyroxene-dominated texture and mineralogy

Augite forms the primary mineral phase throughout this specimen, characterized by a ferrosilite content near zero (Fs ~0.0-0.1) and wollastonite component ranging from Wo ~39.4 to 42.3. These compositional values place the pyroxene in the calcic field, consistent with crystallization from a basaltic melt under conditions similar to those that produce terrestrial gabbros. The equant grain morphology indicates slow cooling rates that allowed crystals to develop isometric shapes rather than elongated or skeletal forms.

Enstatite occurs as a minor phase with ferrosilite content near Fs ~0.1 and wollastonite ranging from Wo ~0.9 to 3.6, representing orthopyroxene that crystallized alongside the augite. Sulfide minerals include chromium-enriched troilite and daubreelite, both of which typically form during late-stage crystallization in reduced environments. Alabandite (manganese sulfide) and the manganese-iron oxide phase represent additional accessory minerals that record the availability of manganese during parent body differentiation.

Scientific context

Ungrouped achondrites represent meteorites that experienced complete melting and differentiation on their parent asteroids but do not share the diagnostic characteristics of established groups like HEDs, angrites, or aubrites. Each ungrouped specimen potentially samples a distinct parent body with its own thermal and compositional history. Ksar Ghilane 022's augite-rich composition and specific pyroxene chemistry distinguish it from all currently recognized achondrite families, suggesting formation on a previously unsampled differentiated asteroid.

Oxygen isotope analyses of acid-washed subsamples place this meteorite on a distinct trajectory in three-isotope space, further confirming its independent origin. The crystallization sequence preserved in this specimen, augite as the primary phase with minor orthopyroxene, indicates a basaltic composition similar to eucrites but with mineralogical and chemical signatures that prevent classification within the HED suite. Understanding the diversity of differentiated asteroids requires specimens like Ksar Ghilane 022 that expand our knowledge beyond well-studied groups. Learn more about meteorite classification and origins at Learn About Meteorites.

Frequently asked questions

Is this meteorite authenticated? Ksar Ghilane 022 is classified in the Meteoritical Bulletin as Achondrite-ung. You can verify the classification at Meteoritical Bulletin: Ksar Ghilane 022. This specimen includes a certificate of authenticity documenting its provenance and classification.

What does "ungrouped achondrite" mean? An ungrouped achondrite is differentiated igneous rock from an asteroid that does not match the mineralogy, chemistry, or oxygen isotope signature of any established achondrite group. Each ungrouped specimen potentially represents material from a distinct parent body.

What is included with this specimen? This listing includes the 1.75g meteorite slice and certificate of authenticity. No display stand is included.

Why are augite crystals significant in this meteorite? The dominance of augite with near-zero ferrosilite content indicates crystallization from a calcium-rich basaltic melt under reducing conditions. This mineral assemblage differs from the augite chemistry in HED meteorites and other achondrite groups, supporting the specimen's ungrouped status.

What caused the calcite veining? Secondary calcite veins form when aqueous fluids carrying dissolved calcium carbonate infiltrate fractures in the meteorite, typically during terrestrial weathering after the fall or find. These veins postdate the original igneous crystallization of the rock.

Collector significance

Ungrouped achondrites occupy a specialized niche in collections because each specimen potentially represents a unique differentiated parent body. With only a small number of ungrouped achondrites recognized in the Meteoritical Bulletin, these specimens document asteroidal diversity beyond the major achondrite groups. This 1.75g slice provides accessible entry into this scientifically significant category at a weight suitable for study collections and educational displays.

The slice format exposes the augite-dominated texture and allows direct observation of the mineralogical features described in the classification documentation. For collectors building representative suites of differentiated meteorites, Ksar Ghilane 022 fills the ungrouped achondrite position with material that cannot be approximated by specimens from established groups. Browse additional differentiated meteorite types in our Ungrouped Achondrites collection.

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