The enthalpies of solution of Cs2Ca[B4O5(OH)(4)](2)center dot 8H(2)O(s) in approximately 1 mol dm(-3) aqueous hydrochloric acid and of CsCl(s) in aqueous (hydrochloric acid + boric acid + calcium oxide) were determined. From these results and the enthalpies of solution of H3BO3(s) in approximately 1 mol dm(-3) HCl(aq) and of CaO(s) in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of -(10328 +/- 6) kJ mol(-1) for Cs2Ca[B4O5(OH)(4)](2)center dot 8H(2)O(s) was obtained from the standard molar enthalpy of formation of CaO(S), CsCl(s), H3BO3(s) and H2O(l). The standard molar entropy of formation of Cs2Ca[B4O5(OH)(4)](2)center dot 8H(2)O(s) was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of Cs2Ca[B4O5(OH)(4)](2)center dot 8H(2)O(s) computed from a group contribution method. (c) 2006 Elsevier B.V. All rights reserved.