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Context: Sequoia is a retrograde kinematic substructure in the nearbyGalactic halo, whose properties are a matter of debate. For example, previousstudies do not necessarily agree on the chemical abundances of Sequoia stars,which are important for understanding its nature. Aim: We characterize thechemical properties of a sample of stars from Sequoia by determininghigh-precision abundances. Methods: We measured abundances of Na, Mg, Si, Ca,Ti, Cr, Mn, Ni, Zn, Y, and Ba from a differential abundance analysis on highsignal-to-noise ratio, high-resolution spectra from new observations and fromarchival data. We compared precisely measured chemical abundances of 12 Sequoiacandidates with those of typical halo stars from the literature, which alsoincludes stars from Gaia-Enceladus. This allowed us to characterize Sequoia andcompare it to another Galactic building block. The comparison was made afterputting all the abundances onto the same scale using standard stars. Results:There are significant differences in [Na/Fe], [Mg/Fe], [Ca/Fe], [Ti/Fe],[Zn/Fe], and [Y/Fe] between Sequoia and Gaia-Enceladus stars at $-1.8\lesssim[\mathrm{Fe/H}]\lesssim -1.4$ in the sense that these abundance ratios arelower in Sequoia. These differences are similar to those seen betweenGaia-Enceladus and in situ stars at a higher metallicity, suggesting thatSequoia is affected by type~Ia supernovae at a lower metallicity thanGaia-Enceladus. We also confirm that the low [{Mg}/{Fe}] of Sequoia is seen inthe literature and in surveys, namely APOGEE DR17 and GALAH DR3, if the starsare kinematically selected in the same way. Conclusion: Sequoia stars have adistinct chemical abundance pattern and can be chemically separated from insitu stars or Gaia-Enceladus stars if abundances are measured with sufficientprecision, namely $\sigma([\mathrm{X/Fe}])\lesssim 0.07\,\mathrm{dex}$.

High-precision chemical abundances of Galactic building blocks. The distinct chemical abundance sequence of Sequoia