Northwest Africa 5206 was discovered in
Algeria during 2007 and purchased by a dealer in Erfoud, Morocco
later in October 2007. The stone was a complete 1276g desert-weathered, brown stone. Hiding under this weathered exterior was
one of the most primitive and highly unequilibrated ordinary
chondrites ever discovered. NWA 5206 was to be later classified
as an Ordinary Chondrite LL3.05 with a Shock Rating of S2 and a
Weathering Level of W3. This meteorite is actually the first and
only chondrite to receive an LL3.05 classification.
The classification makes mention of the
closely packed pristine chondrules with many varieties present.
However, Type I Chondrules (FeO-poor) are dominant over Type II
(FeO-rich) by a ratio of 3:1. There are many chondrule textural
types present in this meteorite including some unique types.
Several heavily mantled chondrules have also been observed
during study and an example of this is viewable in the 6.47g partslice
below. A thin-section image showing a heavily mantled chondrule
taken during study at Northern Arizona is also further down the
page. There is another very rare feature in the partslice below
which is a metallic chondrule. Hutchison (2004) said the
following about this unusual feature:
"Metallic and metal-sulfide chondrules: some
carbonaceous chondrites, notably the CR group, and the most
unequilibrated (type 3) ordinary chondrites have subspherical
metallic or metal-sulfide objects whose dendritic or
polycrystalline textures indicate that they formed during rapid
cooling from melts. Kamacite, with 3-7 wt% Nickel, usually is
the dominant mineral. It may be accompanied by zoned taenite."
"Metal is usually accompanied by troilite in composite spherules
within silicate chondrules, but the sulfide may constitute an
entire spherule or, rarely, an entire chondrule. The spherules
presumably separated from silicate melt as immiscible droplets
of metal-sulfide liquid."
imagery and x-ray mapping at 3000X magnification has shown no
evidence that the homogeneous chondrule mesostasis has undergone
devitrification further indicating the highly primitive nature
of this meteorite. The classification also mentions that NWA 5206
may actually be more primitive than the given 3.05 subtype but
until high quality analyses are performed on chondrule mesostasis
for Potassium and Sodium contents and distributions, a subtype
below 3.05 is not warranted at this time.
6.47g Partslice - MA.10.0009