The polymorphism and dielectric properties of Ba1-xSrxAl2Si2O8 (x = 0.00, 0.01, 0.05, 0.10, and 1.0) feldspars were examined. Strontium additions enhanced the formation of the monoclinic phase, decreasing heat treatment times from three days to 24 hrs. The dielectric constants of all compositions varied between 7 and 8 over a temperature range of -175 to 200 degrees C and at 1, 10, and 100 kHz. An abrupt change (about 5%) in the dielectric constant of Sr-feldspar occurred at -70 degrees C, confirming the existence of the triclinic low temperature polymorph.