Agate is a striped chalcedony quartz that forms in layers and in a wide variety of colors and textures. An individual agate forms by filling a cavity in a "host" rock. As a result, agate often is found as a round nodule, with concentric bands. In ancient times it was said to quench thirst and guard against fever, and agate bowls were very popular in historical Europe.

Prehistoric sharks' teeth may be black, brown, or gray, depending on the minerals in the soil in which they have been buried. Sand at the bottom of the ocean preserved and fossilized the teeth, and wave action uncovers and washes them ashore. Many fossil shark teeth have been collected from the coastal areas of the Gulf of Mexico.