Northwest Africa 5515

Algeria (Coordinates unknown)

Find: Nov. 2007

Carbonaceous chondrite (CK4)

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 (Fa_29-34). Olivine contains 0.2-0.6 wt% NiO. Pyroxenes are present as low-Ca pyroxene (Fs_25-27Wo₁) and augite (Fs_8-10Wo_46-47). Plagioclase composition is heterogeneous ranging An_34-72. 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.

Type specimens: A total of 20 g of sample is on deposit at UTok. MFarmer holds the main mass.