Northwest Africa 4215

Mhamid, Morocco

Find: April 2002

Achondrite (diogenite, unbrecciated)

History: This single stone was bought by Bruno Fectay and Carine Bidaut in Mhamid, Morocco, in April 2002.

Physical Characteristics: A single brown stone weighing 46.4 g and displaying limited patches of fusion crust.

Petrography: (J. A. Barrat, M. Bohn, UBO -IUEM; P. Beck, Ph. Gillet, ENSL) The sample displays a well-preserved cumulative texture, consisting of zoned xenomorphic orthopyroxene grains on the order of 500 µm in size, with a few large chromite crystals (<5 vol%, up to 3 mm). Accessory olivine and scarce diopside grains occur within the groundmass, usually around the chromite crystals. Minor phases are cristobalite (determined by Raman spectrometry), troilite, and metal. This meteorite is weathered and its fractures are filled by calcite, limonite, and gypsum typical of hot desert alteration.

Geochemistry: (J. A. Barrat, M. Bohn, J. Cotten, UBO-IUEM; R. Greenwood, I. Franchi, OU) Orthopyroxenes (En_76.2Wo_1.1Fs_22.7 to En_68.6Wo_5.5Fs_25.9); olivines (Fo₇₆ to Fo₇₁); chromites (Mg# = 14.3–44.0, Cr# = 42.2–86.5) are chemically zoned (EMP). The bulk composition of this stone has been determined for major and trace elements (ICP-AES, ICP-MS). Its FeO, CaO abundances and most of the trace element concentrations (Sr, Ba, Pb, and REE among others) are high and indicate a significant contribution of the secondary minerals (limonite+calcite). In order to remove the terrestrial contribution, a subsample has been leached with hot HCl. The residue, made essentially of orthopyroxene and chromite, is similar in major and trace element abundances to diogenites as shown by the shape of its REE pattern and by its high Al/Ga ratio. Oxygen isotopic: (R. Greenwood, I. Franchi, OU) Were determined on a fraction of the leached powder, δ¹⁷O = 1.431 ± 0.102, δ¹⁸O = 3.203 ± 0.205 relative to V-SMOW, and ∆¹⁷O = −0.248 ± 0.005 (all ‰).

Classification: Achondrite (diogenite, unbrecciated).

Specimens: A total of 10 g type specimen and two polished thick sections are on deposit at ENSL. Bruno Fectay and Carine Bidaut of La Mémoire de la Terre hold the main mass.