Calcium-aluminium-rich inclusion

A calcium-aluminium-rich inclusion or Ca-Al-rich inclusion (CAI) is a centimeter-sized light-colored calcium- and aluminium-rich inclusion found in carbonaceous chondrite meteorites. CAIs consist of minerals that are among the first solids condensed from the cooling protoplanetary disk. The most common and characteristic minerals in CAIs include anorthite, melilite, perovskite, aluminous spinel, hibonite, calcic pyroxene, and forsterite-rich olivine. CAIs were formed at much higher temperatures than the associated chondrules, and may have survived many high-temperature events, whereas most chondrules are the product of a single transient melting event.

The isotopic anomalies of CAIs give valuable clues about the solar system's formation, suggesting that the solar nebula collapsed shortly after a nearby supernova, radiometric dating shows that the CAIs formed about 2 million years before the chondrules formed.

Using lead isotopic data determined on CAIs, an age of 4567.2±0.6 million years can be calculated which can be interpreted as the beginning of the formation of the planetary system. However, due to possible disturbances of the lead isotopic system within the CAIs, this age is possibly only a lower limit of the true age. Also an age of 4571 Ma for CAIs has been given, based on Mn-Cr and Mg-Al isotopic data.