Northwest
Africa 4425
Algeria
Find: May 2006
Carbonaceous chondrite (CK3)
History: Purchased by P. Thomas in May 2006.
Physical characteristics: A complete, ventefacted stone
weighing 579 g, without fusion crust. It has a brownish
color indicating significant terrestrial alteration.
Petrography: (M. Bourot-Denise, MNHNP) Millimeter-sized
chondrules and CAIs observed. The type specimen contains
a 1.5 cm-diameter CAI rimmed with spinel and diopside.
Chondrules are generally porphyritic, with wide rims, and
contain magnetite beads. Large opaque nodules of magnetite
and sulfide are present in the matrix. Matrix is either
crystallized or fine, with abundant small magnetite crystals.
BSE images indicate that this chondrite is not completely
equilibrated; olivines and pyroxene in porphyritic chondrules
are zoned. In the type specimen, there is an angular clast,
2 cm in diameter, containing small, porphyritic pyroxene
chondrules (100-500 µm); chondrules and well-crystallized
matrix are completely equilibrated; magnetite is finely
scattered through the clast and does not make up nodules
as in the host; the interface between the clast and the
host is highlighted by small, euhedral magnetites.
Geochemistry: Olivine (Fa13.6±12.6, range Fa0.54-34.1);
low-Ca pyroxene (Fs16.8±11.0, range Fs2.8-30.7);
magnetite (Cr2O3 = 2.6-3.7, MgO = 0.87-1.15 [both wt %]).
Pyroxene in the angular clast: Fs23.35±0.86. Magnetic
susceptibility (J. Gattacceca, CEREGE) log c = 4.6 10-9
m3/kg.
Classification: Carbonaceous chondrite (CK3, estimated
subtype 3.8); minimal shock and moderate weathering.
Type specimens: A total of 32.8 g of sample (1 sawn fragment)
and two polished mounts are on deposit at MNHNP. Thomas
holds the main mass.
NWA
4425, 30X magnification
© Ph. Thomas (click to enlarge)
NWA
4425, 30X magnification
© Ph. Thomas (click to enlarge)
NWA
4425, 30X magnification
© Ph. Thomas (click to enlarge)
NWA
4425, 30X magnification
© Ph. Thomas (click to enlarge)
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