Hello David,
Silastman is essentially correct.
What he is saying is that the specific heat of liquid water is 4.183 J/g.K. But, above 100C (373K) you will also have to use the latent heat of vaporisation of water (2259 J/g.K).
If there is no evaporation of water in your moist limestone system, the specific heat of the system can be calculated by multiplying the percentage of each component by its Cp and summing the results to give the Cp of the moist limestone ie.
92/100 *.908 + 8/100*4.183 = 1.17 J/g.K
If there is significant evaporation in your system, then you will have to account for the latent heat of vaporisation of the evaporated portion of the moisture, in a similar manner to the calculation above..
Regards,
Ted.