Collection
Classification: Eucrite-melt breccia
Observed fall: No
Year found: 2022
City, Country: Northwest Africa
Mass: 5,85 kg
In collection
Weight #1 : 9,36 g
Weight #2 : 11,84 g
Certificate of authenticity: Yes (2)
NWA 15658 is classified as a Eucrite-melt breccia (EUC), a type of achondritic meteorite originating from the basaltic crust of 4 Vesta. Eucrites are composed predominantly of plagioclase feldspar and pyroxene, reflecting magmatic processes on Vesta’s surface or shallow subsurface. However, the “melt breccia” designation indicates that portions of the rock were partially melted and welded together by impact events, resulting in a brecciated structure where molten material consolidated fragments of pre-existing eucritic rocks. This impact-induced mixing and melting record the intense collisional history of Vesta’s crust. Studying NWA 15658 offers valuable insights into the interplay of volcanic and impact processes on early-formed, differentiated asteroids in the solar system.
Under the light microscope, a thin section of NWA 15658 – a Eucrite-melt breccia reveals angular to subangular clasts of basaltic plagioclase and pyroxene embedded in a partially melted, fine-grained matrix. Many clasts display igneous textures typical of eucrites—interlocking, well-formed feldspar and pyroxene crystals—while others show evidence of shock and fracturing. The matrix often appears glassy or very fine-grained in areas where localized melting occurred, welding the clasts together. Under polarized light, the larger feldspar and pyroxene grains exhibit clear interference colors, whereas the melt-rich regions may show subdued or cryptocrystalline textures. This mixture of intact igneous fragments and impact-induced melt zones underscores the high-energy collisional events that shaped Vesta’s surface.
