The CAI Database: ²⁶Al–²⁶Mg Isotope Systematics

We present a publicly available calcium–aluminum-rich inclusion (CAI) database that focuses on the initial ²⁶Al/²⁷Al₀ ratio in CAIs, designed in a way that researchers in cosmochemistry and astrophysics may find useful. To date, the database contains 497 CAIs from 75 peer-reviewed papers. The CAIs are from all chondrite groups and cover different CAI types, textures, and sizes. The database includes the paper; the host meteorite; the CAI name and type; the ²⁶Al/²⁷Al₀, δ²⁶Mg₀∗, and δ²⁵Mg values and their uncertainties; the number of regression points; the maximum ²⁷Al/²⁴Mg; the mean-squared weighted deviation; the CAI size; and CAI descriptions. We grouped the CAIs in different ways to discuss ²⁶Al/²⁷Al₀ ratio distributions with implications for the CAI formation timeline. Overall, we agree with previous authors that CAIs have a bimodal ²⁶Al distribution: CAIs with robust isochrons (n = 151) have a median ²⁶Al/²⁷Al₀ = 4.8 × 10⁻⁵ (with a 1σ standard error of 0.1), while those with isotopic anomalies (n = 87) have a median ²⁶Al/²⁷Al₀ = 0.3 × 10⁻⁵ (with a 1σ standard error of 0.2). However, the large standard deviation of both groups (1.3 and 2.3, respectively) indicates that the ²⁶Al/²⁷Al₀ values scatter significantly within each population. CAI types and groups can have distinct ²⁶Al/²⁷Al₀ and δ²⁶Mg₀∗, but the unmelted inclusions (n = 33) have the highest median ²⁶Al/²⁷Al₀ = 5.1 × 10⁻⁵ and a low median δ²⁶Mg₀∗ = −0.05‰. We find slightly different ²⁶Al/²⁷Al₀ distributions between CAI chondrite types, but no differences between petrographic types or sizes. These observations can help us to understand CAI formation in the context of astrophysical models.