The Bureau of Mines has measured the low-temperature heat capacities and high-temperature enthalpies of crystalline k2si2o5 as part of a program for advancing mineral resources technology with energy economy. High-temperature enthalpies of glassy and liquid k2si2o5 and crystalline k2sio3 were also measured. An adiabatic calorimeter operation over the range 5 to 308 k was used for the heat capacity measurements for k2si205 from which the standard entropy at 298.15 K, s deg. 298 = 45.55 +/- 0.05 Cal/deg-mole, was calculated. Tabulated values of c deg. P, s deg., -(G deg. -H deg. 0)/T, and h deg. -H deg. O from 5 to 300 k are given for k2si2o5. A copper- block drop calorimeter was used in the enthalpy measurements, operating from 298.15 to 1,198 k for k2sio3 and from 298.15 To 1,453.8 K for k2si2o5. No transitions were found for k2sio3. The k2si2o5 showed two reversible first-order transitions, one at 510 k with a heat of transition of 0.29 Kcal/mole and one at 867 k with a heat of transition of 0.38 Kcal/mole. The heat of fusion for k2si2o5 was calculated to be 8.42 Kcal/mole. Relative enthalpies are given in equation form, and high-temperature values are tabulated for c deg. P, s deg., -(G deg. -H deg. 298)/T, and h deg. - H deg. 298. Also tabulated are ah deg., Ag deg., and log k for formation of k2sio3 and k2si2o5 from both the elements and the oxides.