New insights on the porosity and grain features of Al Haggounia 001, an impact-melt meteorite

In the frame of a broader study on impact effects on meteorites microstructures and mineralogy, we studied the internal structures and grain features of Al Haggounia 001 meteorite, a very interesting EL3 impact melt characterized by a strong porosity. The study was carried out using a 3D reconstruction obtained by micro-Computed x-ray Tomography (μ-CT) supported by chemo-mineralogical characterization obtained by SEM-EDS. The fragments examined consist of a matrix of enstatite, plagioclase, with minor phases such as sulfides, oxides, and phosphides. Only one relict chondrule was observed that consists of a radial pyroxene with enstatite composition, Na plagioclase and silica mesostasis. SEM-EDS analyses reveal that the average composition of pyroxene and plagioclase is (En98.4 Fs0 Wo1.6) and (Ab80 An12 Or8), respectively. The minor phases found are daubréelite, schreibersite, oldhamite, troilite, graphite, tiny kamacite grains survived to the weathering, and N-bearing oxide. In addition to primary phases, terrestrial products as jarosite and halite were found. Kamacite appears variably oxidized. HR-SEM images reveal resorption features as well as rounded etch pits on the surfaces of daubréelite, holes on plagioclase and scalloped enstatite crystals. The μ-CT measurements show an uneven porosity with an average percentage of about 15% that consists averagely of open pores (12%) and closed pores (3%) with irregular to round shapes. The methodological approach based on volumetric investigation provides information about the spatial distribution, volume percentage and shape of voids and mineralogical phases with different density and adds new elements about the origin of porosity in this meteorite.