The heat content above 25.0 Deg c up to 1,000 deg c was measured for six rock types: St. Cloud gray granodiorite, Holston limestone, Sioux quartzite, Rockville quartz monzonite, Salem limestone, and the basalt at Dresser, Wisconsin. The calorimetric data were obtained with an isothermal jacket-copper block calorimeter. The experimental heat content data for each rock type are presented, along with specific heat data obtained from the temperature derivative of the heat content. For the six rock types the maximum deviations of the specific heats at a given temperature were within 10 percent below 575 deg c and within 34 percent above 575 deg c. The increase in the values of specific heat range from a minimum of 13 percent for the basalt at Dresser, Wisconsin. (Temperature range, 100 deg to 1,000 deg c) to a maximum of 46 percent for Holston limestone (temperature range, 100 deg to 870 deg c).