In this paper, a detailed study focused on the characterization of the surface chemical species on the Kansk-Achinsk brown coal chars with different inherent mineral matters, calcium, in particular, and on the evolution of chemical species upon steam gasification at a mild temperature of 700 degrees C was performed by using surface-sensitive X-ray photoelectron spectroscopy, X-ray absorption near edge structure, and other techniques. It was found that the naturally occurring calcium surface species represented highly dispersed carbonate-like forms. Before gasification, they represented aragonite-like species. However, on steam gasification, they readily underwent solid-phase polymorphic transition into a calcite-like form. The main proportion of the surface carbon atoms (68-71%) on all the chars represented sp(2)-hybridized carbons in the graphene fragments, while the remaining 29-32% accounted for as oxidized carbon species of different configurations. Mainly, sp(2)-hybridized carbon atoms were found to be sensitive to activation by a calcium catalyst. The conclusion was drawn that these were highly dispersed calcite-like surface species derived from the aragonite-like ones under steam gasification reaction, which could be responsible for the catalytic activation of sp(2)-hybridized carbon atoms and for the char gasification reactivity.