Archeological studies have demonstrated that many Prehistoric artefacts in obsidian found in the Near East have a chemical affinity with obsidian out-cropping in the Nemrut volcano. In the archaeological literature, Mount Nemrut is considered as one of the most important obsidian sources used by prehistoric societies. During our two field works in 2013 and 2014, we prospected a wide area on and around Nemrut volcano. Our findings confirm the location of the obsidian outcrops described in the literature. According to our observation, obsidian on Mount Nemrut volcano is generally not exploitable for chopping tools. Most of the studied obsidians we defined on the field, present a facies with numerous phenocrysts and cracks, which is not compatible with a good knapping quality. However, we identified a new outcrop associated with obsidian artefacts such as nuclei and rough flakes. Geological samples of the obsidian from this outcrop present all a very different fades compare to those of others Mount Nemrut obsidians: obsidian from this area does not show any phenocryst or cracks, and they are very homogeneous and uniform. These characteristics are in favor to knapping criteria. Comparatively to the other known obsidian outcrops in the Nemrut volcano, we can assume here that this obsidian outcrop is, to date, the only source one that could have been exploited, by Prehistoric people on the Nemrut volcano. Our work, using chemical analyzes (LA-ICP-MS), petrology and field observation enhances characteristics for workable obsidian that depends on the modality of emplacement. This last one should have been different from the other outcrops to provide a different facies.