Density, porosity, and pore morphology constitute the basic physical properties of meteorites.These properties of 214 fragments from 163 different ordinary chondrites (OCs), including falls, non-Antarctic finds, and Antarctic finds, were measured, calculated, and investigated. Of all the measured OCs data, densities, and porosities of 37 OC falls (14 H, 17 L, and 6 LL), 31 non-Antarctic finds (9 H and 22 L), and 95 Antarctic finds (24 H and 73 L) are reported for the first time. The individual masses of all the meteorite fragments measured in this study ranged between 0.8953 and 7.7133 g, and these masses were too low to be measured by the Archimedean glass bead method. Our study indicated that the grain density and porosity of find OCs are significantly reduced by terrestrial weathering. As a result, such OCs are not suitable for their physical propertie study. Shock degree ≤S2 slightly increases the measurable porosities of the meteorites by generating a certain amount of tiny cracks in the silicates to connect some isolated pores with the measurable pores. Shock degree over S2 significantly reduces the porosities of meteorites by compacting or even melting the material. Weathering reduced the porosities via space filling of weathering products. Shock load over S2 reduced the porosities of the meteorites by minerals compressing or melting. Moreover, the shock load over S2 also converted intergrain irregular pores into intragrain cracks. Thermal metamorphism mainly changed the pore morphology (size) by pore merging during mineral recrystallization. The pore morphology also plays a significant role in controlling the friability of OCs.

Context. E-type asteroids have been linked to aubrites, while M-type asteroids have been linked to enstatite chondrites (ECs) and iron meteorites (IMs). However, as ECs and IMs generally lack absorption characteristics, distinguishing their parent bodies by spectroscopy generally poses a challenge. Aims. We aim to develop a method to distinguish two kinds of M-type asteroids, the parent bodies of ECs and IMs, and to infer their composition. Methods. We measured the visible to near-infrared (VIS-NIR) reflectance spectra of aubrite, ECs, and IMs. Then we analyzed and compared their spectral parameters, such as the reflectance at 0.55 µm (R0.55), absorption bands, and spectral slopes. We also compared the geometric albedo and spectral slopes of a total of 13 E-type and 14 M-type asteroids. Furthermore, combining the collected radar albedo and density data of M-type asteroids, we discuss their potential composition at different depths. Results. We find that for most meteorites, with the exception of very weak absorption in an aubrite and an EH7 chondrite, ECs and IMs do not show any absorption characteristics. Aubrite shows extremely high reflectance and a negative near-infrared slope (NIRS) and ECs show relatively low reflectance and moderately positive NIRS, while IMs show relatively moderate reflectance and the steepest positive NIRS. Two diagrams plotting with R0.55 and NIRS calculated in the 1.1–1.2 µm and 1.1–1.4 µm bands were subsequently shown to perform optimally at distinguishing aubrite, ECs, and IMs. In addition, M-type asteroids have a wide range of NIRS and diverse radar albedo and densities, whereby 16 Psyche shows high NIRS, radar albedo, and density, while 21 Lutetia is dominated by low values for these parameters. Conclusions. We demonstrate that NIRS is correlated with metal content and increases with metal content. In particular, the NIRS calculated in the 1.1–1.4 µm band is a potentially useful parameter for inferring the surface metal content of E- and M-type asteroids. Based on our results, we suggest that the featureless M-type asteroids ought to be divided into two subtypes: Mm- (e.g., 16 Psyche) and Me-type (e.g., 21 Lutetia) in the aim of characterizing the sources of IMs and ECs, respectively.