A relatively simple indentation technique for the rapid measurement of fracture surface energy, Γ, of small samples is described. The reliability of this technique is assessed by testing soda-lime glass for which there are good independent fracture mechanics determinations of fracture surface energy. The indentation technique gives a value for Γ of 4.33 J m−2 which compares favourably with the accepted value of 3.8 J m−2. Fracture surface energies of the {010} and {001} cleavage planes of single crystal olivine (modal composition Fo88Fa12) are then determined and compared with theoretical estimates of the thermodynamic surface energy, γ, calculated from atomistic parameters (γ is equal to Γ in the absence of dissipative processes during crack extension). The experimental values for Γ{010} and Γ{001} are respectively 0.98 J m−2 and 1.26 J m−2. The calculated values of γ{010} and γ{001} are respectively in the range from 0.37 J m−2 to 8.63 J m−2 and 12.06 J m−2. The particular advantages of the indentation technique for the study of the fracture surface energies of geological materials are outlined.