We present a method for estimating the relative abundances of refractory elements in the interstellar dust of galaxies hosting damped Lyα (DLA) systems. The method requires gas-phase column densities of volatile and refractory elements, obtained from absorption-line spectroscopy, and interstellar abundances of the same elements, predicted by chemical evolution models of DLA galaxies. We applied this method to the sample of DLA systems with measurements of Mg, Si, S, Fe, and Zn column densities. We find that the dust abundance ratios (Si/Fe)d and (Mg/Fe)d decrease by almost two orders of magnitude in the metallicity range between ≃1/100 solar to roughly solar. This decrease is stronger than the well-known decline of α/Fe ratios with metallicity observed in metal-poor stars and galaxies, suggesting the existence of metallicity-dependent mechanisms of dust production. To cast light on these mechanisms we investigated the contributions of different stellar sources and interstellar processes to the galactic cycle of dust. We find that Type II SNe are important contributors to the dust composition at low metallicity ([Fe/H] < ‐0.6), whereas dust accretion in the interstellar medium appears to be important at higher metallicities, leading to a gradual rise of iron-rich particles, possibly in metal form. To further investigate the nature of the dust, we introduced an idealized model of dust grains based on a mixture of silicates (pyroxenes and olivines) and an iron-rich constituent. The model reproduces the evolutionary trends and suggests that olivines are dominant in silicates, in line with other studies of interstellar dust composition.
