Obsidian

 

This obsidian and shark tooth fossil pendant can be purchased on ebay :

http://www.ebay.com/itm/122059972328?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

Obsidian is a form of silica glass made by the hot lava flow of a volcano. It's not technically a mineral or a glass but this prize substance was extremely useful to early prehistoric humans. It's natural sheen made it useful for 'scrying' by the Aztecs when they made their prophetic messages available to their people. They called huge pieces of obsidian smoking mirrors and looked into the shards for visions of the future.

Earlier in the Americas, huge trade centers were set up for trading obsidian. This substance is usually very dark and sometimes flecked with spots of crystallized white. It's easy to carve and has a natural gloss or sheen. We find obsidian artifacts all over the Americas in the form of jewelry, carved figurines and even spearhead points. 

In it's natural form, obsidian breaks in flecks or shards and the edge of these shards is sharper than a razor edge making it a functional tool for cutting and carving. In fact, the Aztecs used it when performing their sacrifices to the gods.

Obsidian was easily accessed so any region that had obsidian became prosperous through trade. Cities like the ancient Teotihuacan became highly populated and well known by their major trade export of obsidian.