NWA 15468 Ordinary Chondrite Meteorite Slice, OC4 melt breccia, 42.09g, Impact-Molten Matrix

Impact-molten matrix frozen in time

This 42.09g polished slice captures the violent thermal history of an ordinary chondrite transformed by catastrophic impact. The once-discrete chondritic structure melted and recrystallized into a breccia matrix, binding surviving fragments in what was briefly molten rock. The polished surface reveals this impact-generated mosaic with clarity: angular clasts of unmelted chondritic material suspended in a darker, recrystallized groundmass that cooled rapidly after the collision event.

NWA 15468 represents one of only six OC-4 melt breccia classifications recorded in the Meteoritical Bulletin. This specimen preserves both the pre-impact chondritic heritage and the transformative shock event in a single cross-section. The slice measures substantial enough to display the textural variation across multiple impact-processed zones, with some areas showing complete melting while adjacent regions retain relict chondritic features.

Melt breccia texture and shock features

The polished face exposes the characteristic texture of melt breccia formation: chondritic clasts ranging from submillimeter to several millimeters across, set in a fine-grained matrix that formed from impact-generated melt. The matrix itself shows recrystallization textures consistent with rapid cooling after the impact event. Some clast boundaries remain sharp where fragments survived the thermal pulse intact, while other areas show partial melting and diffuse boundaries where material began to incorporate into the melt phase.

Under magnification, the slice reveals shock darkening in portions of the matrix and evidence of localized melting that did not fully homogenize the material. This preservation of both melted and unmelted domains within a single specimen documents the thermal gradient present during the impact event. The polish brings out subtle color variations between the darker melt matrix and lighter clastic components, emphasizing the brecciated nature of this impact-processed material.

Scientific context

Ordinary chondrites dominate meteorite falls, but specimens that experienced sufficient impact energy to generate melt breccias remain scientifically valuable. The OC-4 designation indicates an ordinary chondrite composition with petrologic type 4 characteristics in the unmelted portions, combined with melt breccia textures from later impact processing. This dual record makes melt breccias important for understanding both the original parent body lithology and the subsequent collision history that generated localized melting without destroying the entire meteorite.

The scarcity of classified OC-4 melt breccias reflects the specific conditions required for their formation: impact energy high enough to generate melt, but not so catastrophic as to completely homogenize or destroy the meteorite. NWA 15468 formed in the asteroid belt, where collisions between small bodies generated the shock features and thermal metamorphism now preserved in this slice. For collectors and researchers interested in impact processes, this specimen provides tangible evidence of the energetic environment that shaped early solar system bodies. Learn more about meteorite types and formation at Learn About Meteorites.

Frequently asked questions

Is this meteorite authenticated? Yes. NWA 15468 is classified as OC4 melt breccia in the Meteoritical Bulletin. You can verify the classification at Meteoritical Bulletin entry: NWA 15468. This specimen includes a certificate of authenticity with full classification details.

What does "melt breccia" mean? Melt breccia forms when impact energy generates enough heat to partially or completely melt meteorite material, which then cools and solidifies while incorporating fragments of unmelted rock. The result is a mosaic texture of angular clasts suspended in a once-molten matrix, preserving evidence of the impact event that created it.

What is included with this specimen? The slice weighs 42.09g and ships with a certificate of authenticity documenting its Meteoritical Bulletin classification. No display stand is included.

Why are only six OC-4 melt breccias classified? The specific combination of ordinary chondrite composition, petrologic type 4 characteristics, and melt breccia texture occurs rarely in recovered meteorites. Most ordinary chondrites either lack significant impact processing or experienced different shock conditions that produced other textures. This classification scarcity reflects the narrow parameter window for OC-4 melt breccia formation and recovery.

How does this differ from a standard ordinary chondrite? A typical ordinary chondrite preserves its original chondrule structure largely intact. This melt breccia experienced an impact event energetic enough to melt portions of the material, creating a recrystallized matrix that binds surviving chondritic fragments. The specimen thus records both the original chondritic composition and a later collision history.

Collector significance

The classification scarcity of OC-4 melt breccias makes NWA 15468 a documented rarity in the meteorite market. With only six such classifications recorded, acquiring a specimen of this type requires patience and availability. This 42.09g slice provides display-worthy size with clear textural features visible to the unaided eye, while remaining accessible compared to other rare classifications.

The polished finish maximizes the visual contrast between melt matrix and clastic components, making the impact-processing history immediately apparent. For collectors building representative collections of chondrite subtypes, this specimen fills a category that sees minimal market availability. The slice format offers stable display geometry and exposes the internal texture completely, unlike partial slices or exterior-only individuals. Explore additional chondrite varieties at Chondrites or view other compositionally distinct specimens at Ordinary Chondrites.

Meteoritical Bulletin entry: NWA 15468 | Classification: OC4 melt breccia | Find, Mali, 2022