What is 'The Hope Blue Diamond'? The Hope Diamond is the world’s largest deep blue diamond. It was formed deep in the Earth’s core over a billion years ago. It was brought to the surface by a diamond-bearing volcanic shaft in India. Since its discovery in the early 1600s, it has crossed oceans and continents, and passed through the hands of kings and commoners. It has a notorious past, having been sold, stolen, recovered and re-cut from the French Blue diamond once owned by the French Royal Treasury.