Pachuca, Otumba, and Chicoloapan. Obsidian from Pachuca is notable because of its unique green-gold color and its internal purity which makes it one of the highest quality obsidian sources in Mesoamerica. It was much sought after and widely traded. Green obsidian is also found in the area of Tulancingo, but is distinct from Pachuca obsidian because of its internal opacity (e.g., it is a more milky or clouded green). Substantial research has been carried out to decipher the Guatemala region sources. As mentioned earlier, the Guatemalan region includes the El Chayal, Ixtepeque, and San Martin Jilotepeque sources, located in southern/southeastern Guatemala. Obsidian originating from Guatemala was widely used in Mesoamerica and is found as far north as the Yucatán Peninsula, moving via a well-developed long-distance trade network that inter-connected much of the Maya area. Newer and tentative additions to the Guatemalan source area are Jalapa and Sansare. However, the El Chayal area is often seen as subsuming these two into one large source area. The Pre Classic Monte Alto culture and the Olmecs also used the Tajumulco Volcano source, in the southwest of Guatemala, a source that was almost forgotten during the Classic and Post Classic periods. Analytical methods Trace element analysis Obsidian, a volcanic glass, comes from several geological sources in Mesoamerica, as listed above. Each of these sources has a distinctive “fingerprint” of trace elements that proportionally vary due to the individual circumstances of each source's formation. Neutron activation analysis (NAA) and X-ray fluorescence (XRF) are two analytical methods used to identify the types and amounts of trace elements. These data are then statistically compared to data already available for the known sources. Visual sourcing Visual sourcing is the process by which the source of obsidian artifacts are determined by the analysis of not only their visual appearance (e.g., color, inclusions, etc.) but also their physical attributes, such as surface texture, light reflection, internal opacity, and so on. While not as reliable as trace element analysis, and completely dependent on the experience of the researcher, visual sourcing has a number of advantages. Primarily, it is a cheap method that allows for the analysis of an entire obsidian assemblage. This is in comparison to trace element analysis which, due to high costs, allows for the analysis of only a small sample, preferably one that is statistically representative. Hydration dating Obsidian hydration dating is a method that allows for the