I can be hard, I can be soft. I can scratch my fellow self, or I can be scratched. I'm not always as strong as another version of me. I can be used as a form or communication, as well as presents or luxury. Inside and outside the earth's crust I am made, and waiting times range from one day to millions of years. I come in many colors when I am solid, and I can also be grouped together to make another common solid. Controversy has been made about health concerns in which I am removed from the earth, from disease to sudden death. While a certain few are mentioned above, I grow constantly under your feet. Little do you know you always walk on me, even when you don't try. Mountains, mines, I can be found anywhere, my rarity ranges from diamond to the most common pencil. I am collected, sold, extracted everyday. You use me so commonly that you may not realize I am what I am. I have many different names, hundreds at least, but I am categorized under one name. What am I?