Complex sentence: Tajumulco, El Chayal, Ixtepeque, and San Martín Jilotepeque are the most well-known of the Guatemalan obsidian sources and the most commonly exploited in Pre-Columbian Mesoamerica, in fact, almost all Obsidian found in Olmec and Maya sites is from these sources.
Split into simpler sentences: Tajumulco, El Chayal, Ixtepeque, and San Martín Jilotepeque are the best known obsidian sources in Guatemala and were commonly exploited in Pre-Columbian Mesoamerica. In fact, almost all Obsidian found in Olmec and Maya sites originates from these sources.