Imagine a hobby where you collect something and that something costs nothing, it's totally free, all you need give up is your free time. In addition, that something is available in unlimited quantities in every country around the world and you can collect as much as you can carry most of the time. That something comes in a wide range of colours, is comprised of an equally wide range of materials and does not require any specialist tools to collect what-so-ever, other than a teaspoon and a supply of sampling bags. If you were to start collecting samples of this something you would have an unlimited number to collect, possibly in the region of tens of thousands, possibly even more. That something is sand and the hobby is sand collecting.