Jiddat al Harasis 556 (JaH 556)        19°39.429’N, 55°35.392’E

Al Wusta, Oman

Found: 24 Jan 2008

Classification: HED achondrite (Howardite)

History: A single stone was found during a search for meteorites by E. Gnos, E. Janots, B. Hofmann, and A. Grimberg.

Physical characteristics: Irregular brown 36.647 g stone without fusion crust. Large vesicles (3-5 mm) are visible on the surface and in tomographic sections.

Petrography: (E. Janots, Münster; V. Nentwig, Münster, E. Gnos, MHNGE; B. Hofmann, NMBE): Petrographically heterogeneous rock consisting of lithic and mineral clasts in a finely recrystallized matrix. The matrix consists of clinopyroxene (Fs_30-42Wo_6-15) and plagioclase (An_76-92). Single mineral clasts of Opx (Fs_24-32Wo_2-3), Cpx (Fs_32-39Wo_5-15), olivine (Fa_19-44) and plagioclase (An_76-92) to 0.8 mm. Plagioclase clasts often recrystallized (probably from maskelynite) containing small troilite and ilmenite/spinel inclusions. Two types of rock clasts are distinguished: (1) Clasts consisting of opx (Fs_25-32Wo_2-3) and olivine (Fa_37-41); (2) clasts consisting of opx (Fs₂₀Wo₂), olivine (Fa_20-50), plagioclase (An_61-66). In the rock clasts, olivine can have a mosaic texture. Clasts show different ° of shock (maximum stage 5 with plagioclase recrystallization). Matrix contains remnants of chondrules with Fa_20-23 in center. Although metal is fully weathered to magnetite, hematite and goethite, the shape of oxides indicates former iron melt droplets. Pores are partially filled with secondary anhydrite and celestite and probable clay minerals.

Geochemistry: Bulk chemistry by combined ICP/ICP-MS shows CaO 6.9 wt%, MgO 14.1 wt%, Fe/Mn = 42.5 g/g, Ni 3940 ppm, Co 160 ppm. Oxygen isotopes (I.A. Franchi and R.C. Greenwood, OU): Analyses of thoroughly cleaned pyroxene clast (n=2) and matrix (n=9) yielded, respectively, δ¹⁷O = 1.88, 2.48, δ¹⁸O = 4.02, 4.98, and Δ¹⁷O = -0.23, -0.13 (linearized values).

Classification: Based on mineral chemistry, oxygen isotopes and texture, this is an HED impact melt breccia containing diogenitic and eucritic clasts in roughly equal abundance, consistent with a Howardite classification. Oxygen isotope data of matrix and high Ni abundance indicate admixture of ~10-15% ordinary chondrite (most likely H).

Specimens: All at NMBE.