Within the Museum’s exhibit showing the formation of the earth and its geologic ages are examples of volcanic glass formed from acid (silica-rich) lava: on the top, left is (black, glassy) obsidian - and to the right, this same volcanic material which cooled and hardened before the gas bubbles escaped.
Obsidian, hard but fragile, can be pressure-flaked into projectile points or scrapers and flaked off into narrow blades. The discarded fragments can also be used without retouching, since the edges of a freshly broken piece are as sharp as a razor-blade. The obsidian core and flakes are from the Aztec culture and a part of the exhibit of Mexico and Central America.
