Potash feldspar fractions from the intrusives and country rocks at Gjelleråsen have been studied using X-ray powder method. The potash feldspars of the country rocks far away from the zone of intrusion are triclinic in character. Approaching the contact zones the disordering of the feldspars typically increases. This is indicated by the decrease in tritlinicity values in the same direction. The increasing degree of disorder in potash feldspars has been shown to be resultant of heat transfer across contact zones.