Early Olmec obsidian trade and economic organization at San Lorenzo Hirth, Kenneth ; Cyphers, Ann ; Cobean, Robert ; De León, Jason ; Glascock, Michael D. Abstract Publication: Journal of Archaeological Science Pub Date: June 2013 DOI: 10.1016/j.jas.2013.01.033 Bibcode: 2013JArSc..40.2784H