Abstract <p>Experimental sulfuric acid leaching of quaternary andesite-basalt samples under closed system conditions under the influence of a concentrated sulfuric acid solution has been carried out. A qualitative and quantitative assessment of the effect of sulfuric acid leaching on the composition and properties of andesite-basalts at the first stages of opalization has been carried out. The mechanism of crack formation in andesite-basalts has been revealed due to the uneven expansion of the inclusions and the bulk during the leaching process. A comparison of the natural process of sulfuric acid leaching with laboratory leaching has been made.</p>