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Meteorite Exhibit Information

H5 Chondrite Melt Breccia - NWA 12924

   The process of hot nebular material condensing and accreting into larger and larger masses, and ultimately transforming into chondrules, asteroids, comets, planetesimals, planets, and even the Sun, wasn’t the only mind-bending cosmic process going on in the Solar System's evolution. These things were also being mixed, heated, shocked and just plain blown apart by impacting one another at hypervelocity speeds.

These cataclysmic collisions continue to this day, but most of the orbits of the surviving bodies in our contemporary Solar System have been cleared of other things to hit. So while they do still happen, collisions are much less frequent than they were during the Late Heavy Bombardment period that lasted for several hundred million years from approximately 4.5 to 3.8 billion years ago.

This particular meteorite is a good example of the aftermath of one such hypervelocity collision between celestial bodies. The H in its classification designates it as an Ordinary Chondrite that fits in the high metal category. The 5 indicates the degree of chemical equilibration that has occurred since its formation. However its the "melt" and the "breccia" part in its name that indicates its been through a bit more than your average chondrite.

Indeed when we look closely at it, we can see it is not like the other ordinary chondrites. This one has been melted by at least one intense shockwave, causing the metal to be unevenly redistributed. The matrix has been darkened by shock effect, and the chondrules have been destroyed when the stone was momentarily in a liquid or semi-liquid state. 

Its estimated by some researchers that it would require an impact delivering approximately 60 gigapascal of pressure to the target material to cause the kind of melting seen in meteorites like NWA 12924. As a comparison, it's estimated that the pressure in the Earth's mantle starts at about 23 gigapascals.


Top Meteorite H5 melt breccia chondrite OCC planetarium



Name: NWA 12924

Classification: H5 Melt Breccia

Mass: 560 grams



Top Meteorite H5 Impact Melt


THE DETAILS - Northwest Africa 12924 (NWA 12924)

Place of purchase: Laayoune
Date: January 2018
Mass (g): 5700
Class:H5-melt breccia
Fayalite (mol%):18.8±0.4 (n=8)
Ferrosilite (mol%):16.3±0.2 (n=5)
Wollastonite (mol%):1.3±0.2 (n=5)
Classifier: C. Herd and L. Tunney, UAb
Type spec mass (g):20.1
Type spec location: UAb
Main mass:Mendy Ouzillou, Dustin Dickens 
Comments: Field number MMO-2018-3E
Submitted by C. Herd 



Found in: Niger

Purchased: January 2018

Classification: Ordinary chondrite (H5, melt breccia)

History: Mendy Ouzillou and Dustin Dickens purchased 5.7 kg of stones directly from a dealer in Laayoune, Morocco in January 2018.

Petrography: (C. Herd, UAb) Examination of a ~3 × 4.5 cm slice and a ~1 × 2 cm slice (later used to make the thin section) shows dark-gray rounded clasts containing metal and silicates with some microporosity, surrounded by lighter-gray microcrystalline domains which often have vein-like morphology relative to the clasts. Metal grains in the clasts are mostly <0.5 mm, but locally up to 8 mm in longest dimension. At thin section scale, the clasts consist of poorly delineated chondrules, metal and sulfides in a typical equilibrated ordinary chondrite texture. Microcrystalline domains are glassy in places, and contain fragments of the larger clasts; these are likely shock melt veins. Other shock effects include strong mosaicism in olivine.

Geochemistry: (C. Herd and L. Tunney, UAb) Data obtained by EMP examination of carbon-coated thin section, grey clasts only: Olivine Fa18.8±0.4 (n=8); Low-Ca Pyroxene Fs16.3±0.2, Wo1.3±0.2 (n=5); Feldspar Or2.5Ab81 (n=1).

Classification: Ordinary chondrite, H5-melt breccia. Likely paired with Tassedet 004.

Specimens: Type specimen of 20.1 g, including one thin section, at UAb. Mendy Ouzillou 2.85 kg, Dustin Dickens 2.85 kg.

Link & QR for Meteoritical Bulletin Entry.

 NWA 12924 Dustin Dickens OCC Planetarium

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