Abstract Silicate mineral fibers — stone (Sw) and glass wool (Gw) — are promising resources for cementitious binders. Insights gained from their dissolution kinetics under alkaline conditions can help to control the release of elements, formation of cementitious phases, and understand reactivity of similar type glasses (soda-lime and basalt). Decreasing the liquid-to-solid ratio (L/S) affects the dissolution rate of Sw, whereas the effect was lower for Gw. Residual rate observed for Sw was due to approaching equilibrium between the surface precipitates and solution chemistry. Two types of precipitation products were observed for both fibers at high pH: Mg-Al-Fe LDH and a C-N-(A-)S-H phase with a small concentration of Al. Dissolved Al was observed to incorporate more in LDH at a high L/S, whereas at a low L/S, Al incorporates more into C-N-(A-)S-H gel, altering its morphology. In addition, Ca-Ti-Si-rich globular domes, and Ca-Fe-Ti-rich nano-dome like hydrogarnets on the Sw fiber surfaces were observed.