We present results of the determination of Cl-36 (T 1/2 = 3.0.10(5) a) in rock samples produced in situ by cosmic rays and natural radioactivities. These experiments were designed to determine the feasibility of using Cl-36 for studying erosion processes in calcium rich minerals like limestone or dolomite. The Cl-36/Cl ratios in the samples have been determined with accelerator mass spectrometry (AMS) at the Munich accelerator laboratory. A first application is the investigation of the erosion in the last million years in Allchar (Yugoslavia) for the feasibility study of the geochemical Tl-205 solar neutrino experiment.