Aragonite, like calcite, is a form of calcium carbonate, the same mineral that also forms seashells. In nature, this mineral gets recycled back and forth between living and nonliving forms. If you keep an aquarium, a piece of aragonite will help create a natural, healthy environment for the living creatures inside. You wouldn’t want to use the pretty pieces for this, though, since aragonite will gradually dissolve in water.
Like calcite, aragonite comes in an amazing variety of formations and colors.
The white piece is a type of stalactite sometimes called “cave calcite.”
The little brown piece is a Sputnik aragonite (no one seems to know why, except that the name sounds cute, and the formation looks vaguely like a wee space ship.)
Blue aragonite has a very distinctive color, and this piece has a really cool pick-up-sticks, coral-like formation as well.