These glow-in-the-dark rocks are a unique and practical product. They work by absorbing and storing light, then emitting a bright glow in the dark for several hours before gradually dimming. This process can repeat for many years. They are multifunctional, suitable for various uses such as fish tank decorations, aquarium gravel, fairy garden ornaments, and outdoor decor for yards and walkways. Made of polystyrene resin, they are non-toxic and free of radioactive elements, ensuring no harm to animals. With about 500 pieces in a pack, each rock is around 20 - 30mm long and the total weight is about 900g (2LB). During the day, they serve as excellent decorations with their beautiful and brilliant colors. And in the dark, they provide a great glowing effect, with the glow being brighter in darker surroundings and after more exposure to visible light.