Aztec priests, using razor-sharp obsidian blades, sliced open the chests of sacrificial victims and offered their still-beating hearts to the gods. They then tossed the victims' lifeless bodies ...

Not only is it a visually attractive material, but it can easily be worked to create sharp edges, perfect for spearheads, knives, and hand-axes. Snowflake obsidian has been linked by some to ...