Is the red gem a ruby or a garnet? For the untrained eye, these can be hard to tell apart. But, garnets can be colorless, red, black, or something green! These gems are often found in metamorphic rocks and have been valuable for thousands of years. This volume presented by Scientific American introduces readers to the creation, structure, and properties of garnets. Fun fact boxes offer readers surprising bits of knowledge, such as garnets' use in sandpaper. Beautiful full-color photographs enhance the understandable text. The main content supports knowledge building, a key component of the science of reading.