In this paper, we present an approach to extract feature lines on a 3D mesh. The main problem of classical methods is the difficulty to obtain connectivity of resulting lines. In order to sort out this recurrent problem, we propose an algorithm based on the following ideas. The first one is to label candidate points: they characterize the relevant areas corresponding to the expected features. Our second idea is to unfold this binary flagged mesh into a 2D space in order to use well-known morphological operators. By mapping the resulting output back on the mesh, we get relevant and connected feature lines. We then apply this technique to geological data scans to extract fractures and bench limits.