Everyday Uses of Rocks and Minerals - Shelf 6
The rocks on this shelf are produced by volcanic eruptions. Obsidian forms when lava cools very quickly, forming natural glass. It can be broken to produce extremely hard, sharp edges, which many cultures have used for projectiles and knives. Even today, some surgical scalpels are made from obsidian, as seen at the lower right of the image.
Pumice is also formed by rapid cooling of lava. In this case, the lava is cooling as dissolved gasses are escaping, creating a large number of frozen bubbles in its structure. Imagine freezing a shaken-up cola as it foams out of the bottle. Pumice is used as an abrasive, illustrated here by pre-faded jeans, weathered by rubbing with pumice, and Lava brand soap, which includes pumice as a scouring agent for cleaning extra-dirty hands.