NWA 17918 Diogenite-pm Meteorite Slice, HED Achondrite, 9.29g, Polymict Breccia from Vesta

Polymict diogenite from Vesta's lower crust

This 9.29g slice of NWA 17918 displays the characteristic texture of a polymict diogenite, with multiple fragments of orthopyroxene-rich material embedded in a fine-grained matrix. The slice reveals distinct clast boundaries where different generations of plutonic rock meet, preserving a record of impact mixing in Vesta's lower crust. The specimen's cross-section shows the coarse crystalline structure typical of slowly cooled deep crustal material, with orthopyroxene crystals visible throughout the brecciated matrix.

Found in Algeria in 2025, NWA 17918 joins a limited group of classified diogenites. With only 74 total classifications recorded for this material, specimens remain scarce in both research and private collections. The slice format provides an optimal view of the internal structure, making the polymict nature of the breccia immediately apparent.

Orthopyroxene-dominated lithology

Diogenites consist primarily of orthopyroxene, a magnesium-iron silicate mineral that crystallized from magma deep within Vesta's crust. The polymict designation indicates this specimen contains fragments from multiple source regions, mixed together by ancient impacts. The varying grain sizes and textures within the slice reflect different cooling histories, with some clasts originating from deeper, more slowly cooled layers than others.

The coarse crystalline structure distinguishes diogenites from the finer-grained eucrites that formed closer to Vesta's surface. Under magnification, the orthopyroxene crystals show the blocky, prismatic forms characteristic of pyroxene minerals, with cleavage planes intersecting at roughly 90-degree angles. The darker matrix material between clasts represents impact-generated melt and crushed mineral grains.

Scientific context: Vesta's differentiated interior

Diogenites represent material from Vesta's lower crust and possibly upper mantle, excavated by massive impacts and delivered to Earth as meteorites. NASA's Dawn mission confirmed Vesta as the source of HED meteorites by matching surface spectra with laboratory measurements of these specimens. The polymict nature of NWA 17918 indicates it originated from a region where multiple impact events mixed materials from different crustal depths.

As plutonic rocks, diogenites cooled slowly at depth, allowing large mineral crystals to form. This contrasts with eucrites, which crystallized rapidly at or near the surface as lava flows. Together, eucrites and diogenites provide a vertical sampling of Vesta's crust, offering insight into differentiation processes on early solar system bodies. Learn About Meteorites to understand how these specimens help reconstruct asteroid geology.

Frequently asked questions

Is this meteorite authenticated? Yes, NWA 17918 is classified as Diogenite-pm in the Meteoritical Bulletin. You can verify the classification at the Meteoritical Bulletin database. This specimen includes a certificate of authenticity documenting the classification, weight, and origin.

What does polymict mean? Polymict indicates the specimen contains fragments from multiple parent lithologies mixed together by impact processes. In this diogenite, you can observe clasts of different orthopyroxene compositions and grain sizes, assembled into a single breccia during collisions on Vesta's surface.

What is included with this specimen? You receive the 9.29g slice and a certificate of authenticity. No display stand is included.

Why are there only 74 classifications of this meteorite? NWA 17918 was recently classified in 2025, and the total number of paired specimens submitted for official classification remains limited. This scarcity reflects both the recent discovery and the relatively small amount of material available for distribution.

How does this differ from a eucrite? Diogenites formed deeper in Vesta's crust than eucrites and consist almost entirely of orthopyroxene, whereas eucrites contain mixtures of pyroxene and plagioclase feldspar. The coarser grain size in diogenites reflects slower cooling at greater depths.

Collector significance and display value

Diogenites remain less common than eucrites in the meteorite market, making classified specimens like NWA 17918 particularly desirable for HED collectors. The polymict designation adds scientific interest, as these specimens preserve evidence of impact mixing processes that shaped Vesta's surface. At 9.29g, this slice provides substantial material for examination while remaining accessible for individual collectors building representative HED suites.

The slice format showcases the internal structure more effectively than an uncut specimen, allowing direct observation of clast boundaries and matrix composition. With only 74 total classifications, opportunities to acquire this material remain limited compared to more widely distributed diogenites. This specimen fits naturally into Diogenites collections and complements eucrite and howardite specimens for collectors assembling complete HED Meteorites series representing Vesta's crustal stratigraphy.

Meteoritical Bulletin entry: NWA 17918 | Classification: Diogenite-pm | Find, Algeria, 2025