WATCH: Why seashells are tougher than chalk

WASHINGTON -- Seashells are made mostly of calcium carbonate, also known as chalk, a mineral soft and crumbly enough to use for sidewalk doodles. Yet seashells are tough and resilient. In this video, Reactions explains why seashells are so different, and why you can't use them to draw on your driveway:

American Chemical Society——Bio and Archives

American Chemical Society, ACS is a congressionally chartered independent membership organization which represents professionals at all degree levels and in all fields of chemistry and sciences that involve chemistry.