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?

Minerals. They come in many different colors, and stronger ones scratch weaker ones. Graphite is used to write with (communicate) and diamonds are considered luxurious. Grouped together, minerals make rocks. Coal can cause black lung (disease) and while being mined it can cave in and crush someone (sudden death). More than 3000 minerals are in existence, (hundreds of names), but I am categorized under minerals.

Today's brain teaser courtesy of Braingle.com.