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 polymict diogenites. With only 76 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.

Discovery and provenance

NWA 17918 was recovered in 2025 from the Adrar region of Algeria, totaling 996.87 grams across six stones. The find joins the limited inventory of polymict diogenites available to researchers and collectors, with only a small number of classified specimens of this type circulating worldwide.

Classification was performed by Jose Garcia of ADARA (Petrography and Curation of Astromaterials, Canary Islands, Spain). The type specimen of 20.30 grams is held by MUNA (Museo de la Naturaleza y Arqueologia, Tenerife, Spain), with two thin sections retained at ADARA. The main mass is held by Brian McDonald of Treasure Coast Meteorite Co. The classification was approved 21 December 2025 and published in Meteoritical Bulletin 114.

Petrographic analysis confirmed the polymict diogenite designation based on the coexistence of diogenitic and eucritic pyroxene phases. The diogenitic fraction is dominated by low-calcium orthopyroxene (Fs 28.4 to 33.3, Wo 2.9 to 4.3) with pigeonite, subcalcic augite, and ferroan olivine clasts (Fa 65.5 to 70.9). The minor eucritic component includes low-calcium pyroxene (Fs 62.8), calcic plagioclase (An 83.2 to 85.0), and a silica polymorph. Accessory chromite and minor FeNi metal are also present, with magnetic susceptibility measured at 3.40.

Scientific context: Vesta's differentiated interior

The asteroid 4 Vesta is the parent body of the HED meteorite suite, which includes howardites, eucrites, and diogenites. Vesta is one of the few asteroids known to have undergone full planetary differentiation, developing a metallic core, a silicate mantle, and a crust. Diogenites originated in the deeper crustal layers, where slow cooling allowed orthopyroxene crystals to grow to substantial size before solidification.

NASA's Dawn mission, which orbited Vesta from 2011 to 2012, confirmed the long-suspected link between HED meteorites and this differentiated asteroid. Spectral measurements from Dawn matched laboratory analyses of diogenites, eucrites, and howardites, providing direct evidence that these meteorites originated from Vesta's surface. The polymict diogenites in particular record the violent impact history that excavated and mixed material from various crustal depths.

Frequently asked questions

Is this meteorite authenticated? Yes. NWA 17918 is classified as Diogenite-pm in the Meteoritical Bulletin. The official classification record is publicly available through the Meteoritical Society database.

What does "polymict" mean? Polymict refers to a breccia composed of multiple distinct rock types or fragments from different source regions, mixed together by impact processes. In this case, the slice contains both diogenitic and minor eucritic components.

Where does this meteorite come from? NWA 17918 originated on the asteroid 4 Vesta, the second-largest object in the asteroid belt. It was ejected by an impact and eventually fell to Earth, where it was recovered in the Adrar region of Algeria in 2025.

How is the slice prepared? The specimen was cut using a precision diamond saw and the cut surface was polished to reveal the internal structure. This preparation allows direct visual study of the orthopyroxene clasts and matrix relationships.

Is shipping insured? Yes. All specimens ship fully insured with tracking. Treasure Coast Meteorite Co. handles each piece with care appropriate to its scientific and collector value.

Collector significance

Polymict diogenites represent a relatively scarce subset of the HED meteorite group, with only 76 approved classifications worldwide. The combination of multiple orthopyroxene generations, accessory chromite and FeNi metal, and the rare eucritic component makes specimens like NWA 17918 particularly valuable for collectors building a Vesta-focused reference collection. This 9.29g slice provides a substantial viewing area while remaining accessible to private collectors.

The slice format displays the polymict texture in a way that complete individuals cannot, with clast boundaries and grain relationships immediately visible. Explore additional Vesta-derived specimens in our Achondrites collection.

Meteoritical Bulletin entry: Northwest Africa 17918. 996.87 g | MB 114 (2025).