A petrologic and microstructural study of a compact type A calcium‐aluminum‐rich inclusion from the Northwest Africa 5028 <scp>CR2</scp> chondrite: Implications for nebular and parent‐body processes

Abstract Compact type A calcium‐aluminum‐rich inclusions (CTA CAIs) are believed to have experienced partial melting that erased all information on their original nebular condensation. To investigate this question, we report new microstructural data a CTA CAI, composed primarily of melilite, spinel, and perovskite, in the Northwest Africa 5028 CR2 chondrite. The melilite grains contain low (5–10 mole%) åkermanite contents not compositionally zoned. Spinel perovskite each occur as near endmember compositions MgAl 2 O 4 CaTiO 3 minor V Al, respectively. continuous rim with hibonite around CAI. We extracted two regions interest from interior CAI using focused ion beam techniques for detailed analysis transmission electron microscopy. Evidence thermal processing occurs perovskite–spinel–spinel triple junction an section spinel inclusion within section. parent‐body alteration form Fe‐rich sheet silicates rim, localized amstallite While previous work suggested many CAIs solar nebula, including melting, our show signatures primary condensation can be preserved more refractory phases contained less minerals, namely here has complex history involving gas‐phase condensation, processing, alteration.