The midwestern American state of Iowa is primarily known for its agriculture, earning it the nickname of "Food Capital of the World." While much of its flat land is devoted to growing corn, there are a few semi-precious gems and minerals that can be found mostly in and around its rivers and river basins. Most these materials are derived as pseudomorphs of each other, meaning they're similar in form and shape but have a different composition.
Typical to most bodies of water, both salted and fresh, pearls can be found in some of the shelled mollusks living in Iowa's rivers. Also common to most bodies of water, the chances of locating a pearl within a mollusk is fairly rare, which is what makes it valuable. Pearls are identifiable as smooth, round stones with an iridescent white, silver or pinkish appearance.
Also found in Iowa's rivers is a gem known as false coral. In the water, it's similar in appearance and shape to red coral, but the living organism loses its color once removed from the water. Like coral, the remains of the organism form a hard, porous material that can be used for jewelry.
Likely the most identifiable of the semi-precious gemstones found in Iowa, chalcedony is a type of quartz. While not scientifically distinguished from quartz, it's widely considered by gem collectors and experts as a different item. Chalcedony typically comes in white or blue. The stone is often a variant, or pseudomorph, of coral, meaning a different chemical compound results in the quartz-like material.
Although not typical in Iowa, the presence of natural chalcedony creates a possibility of this particular quartz pseudomorph. Impurities within the chalcedony may occasionally cause a moss-like substance to grow within the stone. Moss agate isn't considered a true agate since it lacks the multicolored banding typically found in the stone, but the change in chemical composition allowing the internal substance to grow is great enough to warrant a separate classification from chalcedony and agate.