If collecting stamps is too boring for you, this day could be something you might like: Collect Rocks Day is observed on September 16, 2021. A rock is a naturally solid aggregate of one or more minerals. Rocks, especially the minerals and metals found in them, have been an important resource throughout human history and essential to human civilization. Why not playing geologist for a day to find out more fascinating things about the material the earth's outer solid layer is made of? Alternatively you could use this occasion for a nice trip into the nature.