NWA 18496 CK6 Carbonaceous Chondrite End Cut 34.78g

A CK6 carbonaceous chondrite end cut

NWA 18496 is a CK6 carbonaceous chondrite, the most thermally metamorphosed grade found in the CK group. This specimen is a 34.78g end cut. One face is sawn to expose the interior of the stone, while the reverse retains its natural exterior, including fusion crust. What the cut face records is a chondrite that spent a long time being cooked deep inside its parent asteroid. Chondrule boundaries have gone soft or vanished entirely, and the matrix around them has recrystallized into a fine grained mosaic shot through with magnetite.

Every specimen we sell is documented against its published Meteoritical Bulletin entry. Treasure Coast Meteorite Co. is an IMCA member, #3323.

Structure and features

This piece is an end cut. One side is a flat sawn face through the interior of the stone, and the opposite side retains the original exterior surface with fusion crust intact. That combination puts the metamorphic texture of the interior and the atmospheric entry surface on the same specimen. For how that crust forms and why it matters, see our page on what fusion crust is.

The petrographic description that follows is taken from the published Meteoritical Bulletin entry for NWA 18496, classified by J. Garcia, ADARA. It describes the meteorite as a whole, based on thin section work, rather than this individual cut.

The thin section shows a well recrystallized chondritic texture. Chondrules are still recognizable but are commonly poorly defined because of extensive thermal metamorphism, with most showing diffuse to obliterated boundaries against a fine grained recrystallized matrix. A few chondrules still preserve internal barred or porphyritic textures, locally displaying relict barred olivine structures. The matrix itself is fine grained and highly recrystallized, made up predominantly of olivine and low-Ca pyroxene with abundant opaque phases. Minor phases are diopside, plagioclase and pentlandite.

Olivine occurs as anhedral to subhedral grains forming a polygonal mosaic, locally showing straight to slightly sutured grain boundaries consistent with thermal equilibration. Low-Ca pyroxene sits interstitial to the olivine as small anhedral grains. Plagioclase is present as interstitial grains and locally as recrystallized patches, which is what indicates the advanced metamorphic grade. Opaque phases are abundant and occur as irregular grains disseminated throughout the matrix and within chondrules, consisting predominantly of magnetite and sulfides and locally concentrated along fractures and grain boundaries. Metal is absent.

Shock features are minor. Olivine and pyroxene show limited fracturing and no planar deformation features are observed, giving a shock stage of S1. Terrestrial weathering is low.

• Classification: CK6 carbonaceous chondrite
• Shock stage: S1
• Weathering grade: low
• Olivine: Fa 26.3 ± 0.2 (FeO/MnO = 97 ± 5; NiO = 0.50 ± 0.09 wt%)
• Low-Ca pyroxene: Fs 24.2 ± 0.2 Wo 1.2 ± 0.3
• Diopside: Fs 7.6 ± 0.1 Wo 46.9 ± 0.3
• Plagioclase: An 42.5 ± 10.4
• Magnetite: Cr2O3 3.71 ± 0.04 wt%

Discovery and provenance

NWA 18496 was purchased from an Algerian dealer in 2022. As with most Northwest African material, no find coordinates were recorded, which is standard for stones that move through the dealer network before reaching a laboratory. If you want the background on how these names are assigned and what the numbering actually tells you, our guide on NWA meteorites explained covers it.

The stone was submitted for classification by Jose Garcia under the internal workname BMD 009, which appears in the published Bulletin record. Classification work was carried out by J. Garcia at ADARA Petrography & Curation of Astromaterials in the Canary Islands. A 20.4g type specimen was deposited at MUNA, the Museo de la Naturaleza y Arqueología in Santa Cruz de Tenerife, along with one thin section retained at ADARA. Per the Meteoritical Bulletin, NWA 18496 comprises 695g across 25 pieces, with the remaining material held by Brian McDonald of Treasure Coast Meteorite Co.

NWA 18496 was approved by the Meteorite Nomenclature Committee on 27 March 2026 and is recorded in Meteoritical Bulletin 115. That approval is what separates a classified specimen from an unclassified one, and it is worth understanding the difference: see the Meteoritical Bulletin explained and how meteorites are classified.

Scientific context

The CK group was defined by Kallemeyn, Rubin and Wasson in 1991, named after the Karoonda fall in Australia. Their work established that CK chondrites are closely related to the CV and CO groups on compositional, textural and oxygen isotope grounds, and that the group is unusual in having no unequilibrated members: every normal CK is metamorphosed, with petrologic grades running from 4 to 6. Reference: Kallemeyn G. W., Rubin A. E. and Wasson J. T. (1991), The compositional classification of chondrites: V. The Karoonda (CK) group of carbonaceous chondrites, Geochimica et Cosmochimica Acta 55, 881 to 892. https://doi.org/10.1016/0016-7037(91)90348-9

A grade of 6 puts NWA 18496 at the top of that range. In practical terms the petrologic number is a measure of how far thermal metamorphism has pushed a chondrite away from its original state, and the textures described in the thin section are exactly what that looks like: chondrules blurred into their surroundings, olivine grains annealed into a polygonal mosaic, plagioclase recrystallized into interstitial patches. If chondrules and petrologic type are new territory, start with what is a chondrite.

The other detail worth sitting with is the absence of metal. Nickel iron metal is the thing most people expect to find inside a chondrite, and in NWA 18496 there is none. Instead the iron is carried in magnetite and sulfides, and in the FeO-rich silicates themselves. That oxidized state is a defining characteristic of the CK group and is part of what separates it from the metal-bearing CV chondrites it otherwise resembles.

Frequently asked questions

What does CK6 mean?
CK is the carbonaceous chondrite group named after Karoonda. The 6 is the petrologic type, which describes the degree of thermal metamorphism the stone experienced inside its parent body. Six is the highest grade found in the CK group, meaning NWA 18496 was heated long and hard enough to substantially recrystallize its matrix and blur its chondrules.

What is an end cut?
An end cut is a piece removed from the end of a larger stone with a single saw pass. It gives you a flat interior face to study alongside the natural exterior on the opposite side, so you get both the internal texture and the original surface of the stone in one specimen.

Does this piece have fusion crust?
Yes. The exterior side of this end cut retains fusion crust, the thin skin of melted rock that forms as a meteoroid burns through the atmosphere. The sawn face on the opposite side exposes the interior.

Is a CK chondrite magnetic?
The Meteoritical Bulletin entry for NWA 18496 records that metal is absent and that the opaque phases consist predominantly of magnetite and sulfides. Magnetite is itself magnetic, so CK chondrites generally respond to a magnet, but that response comes from magnetite rather than from the nickel iron metal found in ordinary chondrites. Our page on whether meteorites are magnetic goes into why a magnet test alone proves very little.

Where is the type specimen held?
A 20.4g type specimen is deposited at MUNA, the Museo de la Naturaleza y Arqueología in Santa Cruz de Tenerife, Spain. One thin section is held at ADARA. Depositing a type specimen with a recognized institution is a requirement of the classification process.

What documentation comes with this specimen?
Each specimen ships with a Treasure Coast Meteorite Co. certificate of authenticity referencing the published Meteoritical Bulletin entry for NWA 18496. Treasure Coast Meteorite Co. is an IMCA member, #3323.

Collector significance

Two things give this specimen its footing. The first is documentation. NWA 18496 is an officially classified CK6, approved by the Nomenclature Committee and published in Meteoritical Bulletin 115, with its full petrography and geochemistry on the public scientific record. You are not buying an attribution, you are buying a stone whose identity is settled.

The second is condition. Weathering grade is low and shock stage is S1, which for a hot desert find means the textures in the cut face are close to what the stone carried when it landed. On a CK6, where the whole interest is in reading metamorphic texture, that matters more than it would on a piece bought for its exterior. Retaining fusion crust on the exterior alongside the sawn interior face adds the other half of the story, showing both what the meteorite did on the way in and what happened to it long before that.

Browse more carbonaceous chondrites, the full range of chondrites, or all stony meteorites.

The complete classification data for NWA 18496, including the full petrographic writeup and geochemistry, is published in the Meteoritical Bulletin Database: Meteoritical Bulletin entry for Northwest Africa 18496.