This study forms a part of Bureau of Mines continuing research on thermal fragmentation of rocks. The potential of internal heating techniques for rock fragmentation is discussed. A concept of rock fragmentation with rapid internal heating of a localized inner volume of rock is advanced. The energy required for rock fragmentation is made available by creating a required volume of localized heating. The fragmentation of rock using the proposed method is analyzed and qualitatively compared with the results of experiments with charcoal granite, Dresser basalt, and Sioux quartzite. High frequency dielectric heating below 100 mhz is used in the study as an example to examine the working of the concept. The selection of operating conditions for the experimental heating is explained. Fragmentation of charcoal granite and Dresser basalt test rock blocks is achieved for localized heating below 550 deg. C. The heated volume required for fragmentation is observed to be less than 2 percent of the test block volume and the electrical energy consumption is in the order of 3.5 to 6.5 Kwhr/m3. The method offers a possibility for in situ fragmentation of rocks favorable for internal heating. The method is highly dependent on rock properties governing internal heat generation. The efficiency of dielectric heating in the experimental study is observed to increase with increasing dielectric loss of the rock material, ranging from about 10 percent in Sioux quartzite to about 50 percent in Dresser basalt.