Using an Atomic Force Microscope (AFM) operated in contact mode under ambient conditions, we have tried to resolve atomically sharp cracks perpendicular to the basal plane of muscovite mica. However, although tip radius of probes of less than 10 nm allowed a lateral resolution of 0.7 nm and the tip-sample adhesive force has been minimized, our experimental results demonstrate that the molecular structure of crack tips can't still be resolved. Even worse, sometimes the tip-sample friction can disrupt the region around the crack tip. This thus leads to the conclusion that one will fail to resolve atomically sharp cracks under ambient conditions by contact AFM. The inability is due to low lateral resolution of contact AFM and strong tip-sample interaction force under ambient conditions. New techniques of scanning samples in liquids and UHV non-contact AFM both of which have true atomic resolution are strongly recommended for future studies.