NWA 17916 CO3 Carbonaceous Chondrite Meteorite Slice, 12.00g, Mirror Polished Face

NWA 17916 CO3 carbonaceous chondrite slice, 12.00 grams

This slice weighs 12.00 grams and was cut from NWA 17916, a CO3 carbonaceous chondrite found in 2025 in Tindouf, Algeria. One face carries a mirror polish. The reverse retains the saw cut from sectioning, left as worked rather than finished. Part of the perimeter retains intact primary fusion crust, and pale caliche remains along one edge.

Structure and features

The polished face carries a dense population of chondrules set in a fine grained dark matrix. The Meteoritical Bulletin records a mean chondrule diameter of 247 plus or minus 116 micrometres across 36 measured examples, with clear boundaries and minimal alteration at the margins. The textural types identified in thin section include porphyritic olivine, barred olivine and radial pyroxene, and examples of each can be picked out on a polished surface at this size.

Calcium-aluminium-rich inclusions are present in this meteorite, averaging 332 plus or minus 102 micrometres across 34 measured examples, with sharp outlines and fine grained high temperature mineral phases. CAIs are the oldest dated solids in the solar system, and their presence is one of the features that separates carbonaceous chondrites from the ordinary chondrite groups.

The opaque component of the matrix is dominated by troilite and magnetite, occurring as dispersed grains and as interstitial filling between silicate components. Across the cut face the matrix carries brown and orange colouration. The Bulletin records the weathering grade for NWA 17916 as low and notes that no significant weathering products were observed in thin section, indicating minimal terrestrial alteration.

Two different materials sit on the outer edge of this slice and they are worth telling apart. Part of the perimeter retains intact primary fusion crust, the outer skin formed as the surface of the stone melted during its passage through the atmosphere. The Bulletin records the recovered stones as brown in colour with desert varnished fusion crust. Separately, a band of pale tan caliche adheres to one edge and shows as light veining through the edge profile. Caliche is a calcium carbonate deposit that forms around stones lying in arid soils, and it is common on meteorites recovered from the Sahara. It sits on the exterior of the stone rather than being part of the meteorite, and it has been left in place here rather than cleaned off.

Discovery and provenance

NWA 17916 was found in 2025 as two stones with a combined total known weight of 742.17 grams, brown in colour with desert varnished fusion crust. The find location is recorded as Tindouf, Algeria, the place of purchase as Morocco, and the finder as anonymous. The Bulletin records that the meteorite was purchased from a meteorite dealer.

Classification was performed by J. Garcia, ADARA, in the Canary Islands, Spain. The type specimen of 20.35 grams is held by MUNA, the Museo de la Naturaleza y Arqueologia in Santa Cruz de Tenerife, Spain, with three thin sections retained at ADARA. The remaining mass is held by Brian McDonald of Treasure Coast Meteorite Co. The working name recorded in the Bulletin is BMD 016. Classification was approved 14 September 2025 and published in Meteoritical Bulletin 114, Meteoritics and Planetary Science volume 61, pages 942 to 946. The CO3 designation rests on mineral composition, magnetic susceptibility of 4.39, and chondrule diameter.

Scientific context

CO chondrites take their group name from Ornans, the French fall that defines the type. The group is distinguished by chondrules that are small by the standards of chondritic meteorites, set in a matrix that makes up a modest fraction of the rock by volume. That combination is what produces the densely packed appearance on a cut face.

The petrologic type 3 designation records that the material escaped significant thermal processing on its parent body. Chondrules retain their original textures and boundaries rather than having been recrystallised, and compositional differences between individual chondrules survive. Olivine composition in NWA 17916 is recorded at Fa 18.2 plus or minus 11.1, and the width of that spread is itself a marker of a type 3 assemblage, since thermal metamorphism drives such compositions toward a single equilibrated value. Further specimens are held in the Carbonaceous Chondrites collection and the broader Chondrites collection.

Frequently asked questions

What does the CO3 classification mean?
CO identifies the Ornans group of carbonaceous chondrites. The 3 is the petrologic type and indicates that the material has not undergone significant thermal alteration on its parent body.

Why is one face polished and the other left as a saw cut?
The polished face is the display surface and carries the mirror finish. The reverse is left as cut. Finishing a single face is normal practice on slices intended for display in a stand or frame.

What is the pale material on the edge?
Caliche. It is a calcium carbonate deposit that forms around stones lying in arid soils, and it is common on meteorites recovered from desert environments. It is terrestrial material sitting on the outside of the stone, not part of the meteorite. It can be removed, and it has been left in place on this slice.

What is the fusion crust, and how is it different?
Fusion crust is the outer skin formed when the surface of the stone melted during atmospheric entry, so it is part of the meteorite itself rather than something acquired on the ground. The Meteoritical Bulletin records the NWA 17916 stones as carrying desert varnished fusion crust. Only slices cut from the outer portions of a stone carry any crust at all.

What are the small round objects on the cut face?
Chondrules. They are droplets of molten silicate that crystallised in the solar nebula before the parent asteroid assembled, and they are among the oldest solid material available to collectors. The Bulletin records a mean diameter of 247 micrometres for this meteorite.

What does NWA mean in the name?
NWA stands for Northwest Africa and is applied to meteorites recovered from that region without a precisely documented find site. The number that follows is a sequential identifier assigned on classification. Our guide to NWA meteorite designations covers this in full.

How can I verify the classification independently?
The Meteoritical Bulletin Database is public and free to search. Our page on understanding the Meteoritical Bulletin explains how to read an entry field by field.

Collector significance

A polished CO3 face shows the group's defining texture directly, which is not something a complete stone conveys. On this slice the chondrule population and the CAIs are both readable across the full cut surface, while the surviving crust and the caliche on the edge keep the connection to the stone's original exterior and to the ground it was recovered from. At 12.00 grams the piece gives that full face at a fraction of what a complete individual of the group commands. As recorded in the Meteoritical Bulletin database in August 2026, NWA 17916 is one of 686 approved meteorites classified as CO3.

This specimen is cut from a meteorite with a documented classification record. The full entry, including petrographic data, geochemistry, type specimen holding and approval date, can be read at the Meteoritical Bulletin Database entry for Northwest Africa 17916.