Crystal structures of four aragonite-group carbonates-aragonite (Ca 0.997 Sr 0.003 CO 3 ), calcian strontianite (Ca 0.147 Sr 0.853 CO 3 ), cerussite (Ca 0.001 Pb 0.999 CO 3 ), and witherite (Sr 0.019 Ba 0.981 CO 3 )-have been refined at ambient conditions, and thermal expansion has been measured over a range of temperatures from 143 to 586 K by single-crystal X-ray diffraction. Average linear thermal expansion coefficients α 0 (V) are 58(2), 58.3(7), 64(2), and 57(2) (× 10 −6 K −1 ) for aragonite, strontianite, cerussite, and witherite, respectively, throughout the experimental temperature range. Aragonite, strontianite, and witherite have very similar α 0 (V) values, whereas that of cerussite is significant larger, primarily due to the caxis thermal expansion for cerussite being much larger than those of the other carbonates. There are no significant differences for α 0 (a) values among the four carbonates, whereas α 0 (b) values decrease in the order of aragonite > strontianite > cerussite ≈ witherite, and α 0 (c) values increase in the order of aragonite < strontianite < witherite < cerussite. Crystal structures were refined for aragonite (184 to 527 K). <Ca-O> vs. T (K) is fitted linearly quite well, with a slope of 5.8(8) × 10 −6 (Å/K). Corrected for assumed rigid body motion, the CO 3 groups showed no significant change in C-O distances over the temperature range.