Birthstone Month- April Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temprature and presuure, another solid form of carbon known as graphite is the chemically stable form, but diamond almost never converts to it. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are utilized in major industrial applications such as cutting and polishing tools. They are also the reason that diamond anvil cells can subject materials to pressures found deep in the Earth.