Technically, carbon is a rock, and it's in EVERYTHING you eat, as one of the building blocks of life as we know it.
Er, no. Carbon has several forms, or crystallic structures, one of which is diamond. A gemstone, but technically not a rock.
More stable (indeed most stable) is graphite, which is what's most likely used for "lead" in your pencil.
Carbon chemistry is also known as "Organic Chemistry", and is indeed the corner stone of all living things on this planet (with the possible exceptions of a few sulphurbased bacteria, but I'm not sure they were really real), as well as all things we can digest. Ofcourse, carbon is also the basis for such compounds as crude oil and its derivative products, plastic and many other things.
This is why I always have trouble deciding wether to laugh or cry when I hear about the "low carb" diet. It tell you to eat few or no carbonhydrates. But "carbonhydrate", to a chemist, means something based mainly on carbon and hydrogen, which is just about anything we can digest, except water!. Indeed, if you refrain from eating things that contain carbon and hydrogen, I can assure you you will loose wieght, and fast at that!
Yes, I know that's not what's meant when the dietists talk about "carb", but that's such impressise use of language. Why can't they just call them
sacharides, and not sound quite so intolerably stupid and uneducated?