@article {,
	title = {Obsidian Trade at San Lorenzo Tenochtitlan, Mexico},
	journal = {Science},
	volume = {174},
	year = {1971},
	pages = {66-671},
	author = {Cobean, Robert H. and Coe, Michael D. and Perry, E. and Turekian, K. and Kharkar, D.}
}