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Northwest Africa 4560 (NWA 4560)

Northwest Africa 4560 (NWA 4560) was found in the Sahara Desert in Northwest Africa in June, 2006. Five stones totalling 900g were found with a varnished crust which displayed inclusions and an obvious chondrule-rich interior. NWA 4560 was originally classified as an LL3.7 but after further extensive studies it was found that this meteorite is actually an extremely unequilibrated LL3.1 while the Shock Rating is S2 and the Weathering Level is W2. The five stones were all slightly different and the first specimen below was taken from a brecciated 'dual lithology' stone which has two very distinct halves. The second slice at bottom shows distinctive black inclusions. NWA 4560 also shares some remarkable similarities with NWA 3119. The specimens below are part of the Meteorites Australia Collection (MA.07.0003 & MA.07.0033).

6.72g Complete Slice - MA.07.0003

Lithology 1: (Left in first image) has fewer chondrules and much more of the orange/yellow interstitial matrix. The chondrules also appear to be slightly more equilibrated than the other lithology and there are more chondrule fragments. There is a fragmented Bleached Chondrule in the centre of the first image on the border of the two halves. The metal in this half is in slightly larger grains/clumps than the other and Troilite (FeS) is also much more plentiful.

Lithology 2: (Right in first image) has more defined crisp chondrules which are set in a darker but hardly noticeable matrix. In fact, most of what appears to be matrix between the larger chondrules are primarily tiny chondrules. Metal is also finer and distributed more evenly although there is a relatively large armoured chondrule towards the bottom centre edge.

NWA 4560 (LL3.1, S2, W2) - 6.72g Complete Slice
NWA 4560 (LL3.1) - 6.72g Complete Slice.

Enlargement ---> 1200 x 991 (493KB)

NWA 4560 (LL3.1, S2, W2) - 6.72g Complete Slice
NWA 4560 (LL3.1) - 6.72g Complete Slice.

Enlargement ---> 1200 x 998 (524KB)

NWA 4560 (LL3.1, S2, W2) - 6.72g Complete Slice
NWA 4560 (LL3.1) - 6.72g Complete Slice. (Annotated Image)

Enlargement ---> 1200 x 991 (500KB)

 

10.92g Complete Slice - MA.07.0033

Side 1: The most notable feature in this slice is the large black inclusion. It is possible that this inclusion may have been created through a shock event; probably before being accreted. The centre of this inclusion is considerably different to the outer edges. In fact, the centre chondrules are more defined and whole than those at the outside. The outer material appears to be more fragmented and much smaller. But the most tell-tale sign of a shock origin is that the outer chondrule fragments actually swirl in a river around the centre whole ones. Much like you would expect to see in a good example of an Impact Melt Breccia. (Swirl direction/flow is indicated by the blue arrows in the image below.) The smaller black inclusion is similar but seems to have a slightly darker and more plentiful matrix. There also appears to be a very small river of fragmented chondrules within this inclusion too. One of the larger chondrules also has numerous relatively large (~0.5mm-0.75mm) bright pale-green crystals which may be Hypersthene. There are also a few very small variable chondrule fields (VCF) where certain areas seem to show less metamorphosed, crisp chondrules with little to no matrix. The pale lithology/breccia clast at the bottom of the slice shows sharp but more equilibrated chondrules along with more prevalent metal than darker lithology. The darker lithology also has numerous Troilite (FeS) blobs.

Side 2: Shows the other side of the pale lithology/breccia clast along with two more black inclusions. The larger has a darker and more featureless matrix along with smaller chondrules/chondrule fragments while the smaller is even darker with a few ghost chondrules. The variable chondrule fields (VCF) are also present with a larger one at the top centre/right.

NWA 4560 (LL3.1, S2, W2) - 10.92g Complete Slice
NWA 4560 (LL3.1) - 10.92g Complete Slice. (Side 1)

Enlargement ---> 1000 x 680 (285KB)

NWA 4560 (LL3.1, S2, W2) - 10.92g Complete Slice
NWA 4560 (LL3.1) - 10.92g Complete Slice. (Annotated Image - Side 1)

Enlargement ---> 1000 x 680 (285KB)

NWA 4560 (LL3.1, S2, W2) - 10.92g Complete Slice
NWA 4560 (LL3.1) - 10.92g Complete Slice. (Annotated Black Inclusion)

Enlargement ---> 1200 x 967 (513KB)

NWA 4560 (LL3.1, S2, W2) - 10.92g Complete Slice
NWA 4560 (LL3.1) - 10.92g Complete Slice. (Side 2)

Enlargement ---> 1000 x 697 (303KB)

NWA 4560 (LL3.1, S2, W2) - 10.92g Complete Slice
NWA 4560 (LL3.1) - 10.92g Complete Slice. (Annotated Image - Side 2)

Enlargement ---> 1000 x 680 (285KB)


 

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