NORTHWEST AFRICA 5515 (CK4)

Meteoritic Bulletin 96

History: The meteorite was purchased in Munich, Germany in Nov. 2007 from a meteorite seller from Erfoud, Morocco. The meteorite was claimed by the Moroccan to have been found in Algeria. Over one-half of the stone, weighing 7 kg, was purchased by Michael Farmer. The remaining 6.7 kgs was sold to another meteorite dealer.

Physical characteristics: The total mass is 13.7 kgs. It consists of two pieces (7 and 6.7 kgs) that fit together to make a whole stone.

Petrography (T. Mikouchi, UTok): This meteorite shows an equilibrated texture composed of rare scattered chondrules reaching ~1 mm, embedded in fine-grained recrystallized matrix. The grain sizes of matrix minerals are generally several tens of µm. There are abundant irregular-shaped nodules reaching 0.5 mm in size similar to CAI. They are mainly composed of plagioclase and magnetite. Al-rich spinel is nearly absent. The effect of shock metamorphism is minor, but some olivine grains show undulatory extinction.

Mineral compositions and geochemistry: Olivine is equilibrated (Fa29-34). Olivine contains 0.2-0.6 wt% NiO. Pyroxenes are present as low-Ca pyroxene (Fs25-27Wo1) and augite (Fs8-10Wo46-47). Plagioclase composition is heterogeneous ranging An34-72. Magnetite is Cr-rich (Cr2O3 = 5 wt%). Noble gas analysis gives the cosmic-ray exposure ages of T(21Ne)=16 Ma, T(38Ar)=13 Ma and T(3He)=14 Ma (K. Nagao, UTok).

Classification: Carbonaceous chondrite (CK4); minimal shock, moderate weathering.