NWA 5554 was discovered in the Sahara Desert
in Northwest Africa and purchased from a Moroccan dealer at the
St. Marie-aux-Mines show (France) in 2008. It was a single stone
weighing 1684g which was later classified as a rare brecciated
transitional chondrite H/L3-6 with a Shock Rating of S2 and a
relatively low Weathering Level of W1/2.
This meteorite is a breccia with a number of
various features and lithologies. The two most obvious are the
lighter grey areas and the darker brown. The light grey
lithology appears to be more metamorphosed and has more
bleached chondrules. There is
also much more visible metal and it is more porous than the brown
lithology. The brown lithology has many more tightly packed
chondrules which are also generally smaller in size. This
type-3 area is almost devoid of visible metal but curiously has
a number of large troilite (iron sulphide) inclusions.
The bleached chondrules are unusual in that
many of them appear to have either gone through bleaching twice
or were part of an interrupted bleaching process. Several
chondrules have been fractured or broken and display a heavier
bleached zone around the chondrule exterior with a finer
bleaching along the fractures and broken edges. A few are also
bleached all the way through with a very thin unbleached zone
just under the chondrules exterior surface.
Another obvious feature of NWA 5554 are the
large white-grey inclusions or chondrules. One of the smaller
appears to be a heavily bleached broken radiating chondrule but
the others are unknown as to their origin. They may be CAI's but
a far more likely scenario is that they are very large bleached
[or a similar process] porphyritic chondrules.
There also appears to be a dark lithic
fragment which is visible along the bottom of the slice in the
first two photographs. Parts of it contain extremely small pale
chondrules in one pocket while the other darker side is devoid
of any features except several small vesicles. One possible
origin is that it may be the remnants of an impact melt vein
which could have been created during the brecciation event. This
feature is also visible in more detail at the top of the slice
in the 6th and 7th photos.
The last two images show two very unusual
chondrules which have not been seen to this degree in any other
Meteorites Australia Collection piece. These chondrules are in
crystal-form meaning that they are transparent-translucent. They
are a bright green colour which may indicate a composition of
This complete slice of the NWA 5554 stone
below measures 85mm x 64mm at widest points and weighs 34.97g.
It is part of the Meteorites Australia Collection