Compositions comprising surface-modified nanocalcite particles dispersed in a curable resin system comprising a vinyl ester, and coatings and fibrous composites incorporating such compositions are described. The surface-modifying agents include a binding group ionically associated with the calcite and a compatiblizing segment, compatible with the curable resin. The surface-modifying agent may also include a reactive group capable of reacting with the curable resin system. Methods of preparing nanocalcite composites and coating a fibrous composites prepared from such nanocalcite composites are also described.