I'm not quite sure I know where you are going with that question, but basically diamonds are 'rocks' because they are naturally occurring substances - better yet, naturally occurring crystalline substances. Speaking more specifically, they aren't actually 'rocks'. Diamonds are minerals: crystalline carbon mineral. read more
Speaking more specifically, they aren't actually 'rocks'. Diamonds are minerals: crystalline carbon mineral. Rocks are (usually) made up of many different minerals (or many small fragments of one or several minerals. Diamond is a mineral that occurs most commonly in a rock called 'kimberlite' which is a deep-sourced igneous rock. read more
Diamond is considered a mineral, and individual diamonds in nature are individual mineral crystals. read more