Northwest Africa 4679 (NWA 4679)

Northwest Africa 4679 (NWA 4679) was discovered in the form of a single stone weighing 735g in the Sahara Desert in Northwest Africa. It was classified as a rare Carbonaceous Chondrite, CK4 with a Shock Rating of S2 and a Weathering Level of W3. The classification petrography stated that the there are large chondrules of mainly POP (Porphyritic Olivine-Pyroxene - contains crystals of both Olivine & Pyroxene) texture in the bulk of the matrix averaging 1mm-2mm in diameter. The ratio of chondrules to matrix is approximately 50/50. Many of the chondrules in NWA 4679 are also rimmed. NWA 4679 also has numerous CAI's (Calcium-Aluminium-Rich Inclusions) which are not usually so prevalent in CK chondrites. They average 3mm-4mm in size but some are considerably larger. Examples of these white inclusions are visible in the photographs below.

The main and most unusual feature of this meteorite is the very large featureless dark inclusion. The classification mentions that this inclusion is of another petrological type Carbonaceous Chondrite which is most likely CO or CM. However this result was the product of a hand-lens analysis as the inclusion was not thin-sectioned. Another theory of origin for this inclusion could be that of a shock event. This may be evident when looking at the termination line between the host meteorite and the dark inclusion. In the slice below there are a couple of features on that border which are present in both areas. The first of which is in the first image below where there is a small, long (aligned North/South in the image) CAI at the very top point of the dark inclusion. The second is a rimmed chondrule which is even more interesting and is located slightly lower and to the right of the first CAI. While not completely gone, the bottom half of this chondrule has been 'disrupted' inside the inclusion with its basic shape still easily recognisable under 10X magnification. This specimen is part of the Meteorites Australia Collection (MA.07.0014).