NWA 18592 Mesosiderite Meteorite Complete Individual, Stony-Iron, 161.00g, Remnant Fusion Crust

A complete individual mesosiderite with remnant fusion crust

NWA 18592 is a 161.00g complete individual stony-iron meteorite from the mesosiderite class, displaying remnant patches of black fusion crust against the weathered exterior. Mesosiderites are one of the rarest meteorite types known, comprising less than 0.3% of all classified falls and finds. This specimen was recovered in Northwest Africa, classified in 2026 by D. Sheikh at Cascadia Meteorite Laboratory, and accepted by the Meteoritical Society in May 2026.

The complete individual form means this specimen retains its full atmospheric entry shape rather than being cut from a larger mass. The dark fusion crust, formed during the brief seconds when the meteorite blazed through Earth atmosphere, remains visible across portions of the surface. Mesosiderites are mixtures of roughly equal parts metallic iron-nickel and silicate rock, making them visually and structurally distinct from any other meteorite class.

Structure and features

Mesosiderites display a brecciated texture in which metallic iron-nickel and silicate clasts are intermingled in roughly equal proportions. The silicate component of NWA 18592 contains low-calcium pyroxene clasts up to 1 millimeter, often with high-calcium pyroxene inclusions, along with lesser plagioclase feldspar. Accessory minerals include silica, merrillite, troilite, and chromite. The classification work documents moderate shock and moderate weathering throughout the specimen.

The metallic phase in this specimen has been substantially converted to iron hydroxide weathering products, common in mesosiderites recovered from desert finds. Patches of original fusion crust survive on portions of the exterior, dark and contrasting against the weathered surface. As a complete individual the specimen carries a distinctive sculpted exterior shape produced by ablation during atmospheric passage.

Discovery and provenance

NWA 18592 was recovered in Northwest Africa in 2024 and submitted for classification through Cascadia Meteorite Laboratory. The total known weight is 903 grams distributed across 11 stones, with the main mass held by Brian McDonald. A 24.6 gram type specimen is held at Cascadia. Classification was completed by D. Sheikh and accepted into the official record in May 2026, published in the Meteoritical Bulletin Database.

Geochemical analysis confirmed mesosiderite classification with low-calcium pyroxene composition of Fs33.8 plus or minus 1.3 and Wo3.7 plus or minus 0.4, high-calcium pyroxene composition of Fs18.4 plus or minus 2.0 and Wo38.5 plus or minus 3.2, and plagioclase composition of An94.6 plus or minus 1.6. These compositional ranges are diagnostic of the mesosiderite parent body and distinguish this specimen from other stony-iron meteorites such as pallasites.

Scientific context

Mesosiderites represent one of the most puzzling meteorite classes known. Their formation requires the violent mixing of crustal silicates with molten metallic core material, a combination that is difficult to reconcile with standard models of asteroid differentiation. The leading hypothesis involves a catastrophic collision between a differentiated parent body and the metallic core of a smaller asteroid, with the resulting debris recombining under conditions that allowed both phases to coexist in roughly equal abundance.

The presence of low-calcium and high-calcium pyroxenes along with calcium-rich plagioclase places mesosiderites in the broader igneous achondrite family, sharing some compositional similarities with HED meteorites believed to originate from Vesta. The high metal content separates mesosiderites from the achondrites and places them in the stony-iron meteorite group along with pallasites, though the two classes formed under very different conditions.

Frequently asked questions

Is this meteorite authenticated? Yes. NWA 18592 is an officially classified meteorite. See the official Meteoritical Bulletin entry. This specimen includes a Certificate of Authenticity issued by Treasure Coast Meteorite Co., IMCA #3323.

What makes a mesosiderite different from other stony-iron meteorites? Stony-iron meteorites come in two classes: pallasites and mesosiderites. Pallasites contain olivine crystals embedded in iron-nickel metal and formed at the core-mantle boundary of a differentiated asteroid. Mesosiderites contain brecciated silicate clasts mixed with metal in roughly equal proportions and formed through catastrophic impact mixing. They are visually and texturally distinct.

What is fusion crust and why does it matter? Fusion crust is the dark glassy coating produced when a meteorite passes through Earth atmosphere at hypersonic velocity. The outer layer of the stone briefly melts and then solidifies as the meteorite slows below ablation speed. Surviving fusion crust is a key authentication feature and is more commonly preserved on complete individuals than on cut specimens.

What does complete individual mean? A complete individual is a meteorite that has not been cut, sliced, or fragmented since recovery. It retains its full atmospheric entry shape, including any fusion crust, oriented features, and regmaglypts. Complete individuals are generally more desirable to collectors than cut fragments of equal weight because they preserve the natural form of the specimen.

What is included? The specimen pictured plus a printed Certificate of Authenticity. The COA documents the official classification, weight, and provenance through Treasure Coast Meteorite Co., IMCA member #3323.

Collector significance

Mesosiderites are among the rarest meteorite classes, comprising fewer than 250 distinct classifications worldwide and representing less than 0.3% of the entire meteorite catalog. NWA 18592 was newly classified in 2026 with a modest 903 gram total known weight distributed across 11 stones, which places it among the smaller mesosiderite finds and increases the relative importance of each surviving piece. The complete individual form with surviving fusion crust makes this specimen particularly desirable for collectors building a representative stony-iron section.

Meteoritical Bulletin entry: 903g TKW | MB 114 (2026)