Diamond is a gemstone that consists entirely of carbon (C). It is typically colorless and is the hardest natural mineral on Earth because of its very dense crystal structure (the Greek word adamas translates to ‘unbreakable’ in English). It is formed at high temperatures and pressures in the mantle and as a result it is metastable at Earth’s surface. Diamond is a precious stone commonly used in jewelry, together with sapphire, ruby and emerald.
Information source: Mindat.org
Image: White diamond crystal found in South Africa. Source: Parent Géry, Wikimedia Commons.