Physical Properties
Diamonds register a 10 on the Mohs hardness scale, making them the hardest of all gems and indeed, diamond is the hardest natural substance on Earth. These precious stones are made of the same element -- carbon -- as coal, but in the case of diamonds, the carbon is highly compressed. Blue diamonds obtain their color from the presence of boron in the stone.
Cullinan Diamond
In 1905, the largest rough diamond ever mined was found at the Premier Diamond Mine in South Africa. The rough, named the Cullinan Diamond, after the chairman of the mine, weighed 3,106 carats. Two of the largest pieces cut from the Cullinan rough are in the British Crown Jewels; several others are in Queen Elizabeth II's private collection. Cullinan also had nine of the small blue diamonds from the rough made into an exquisite necklace for his wife, Annie.
Hope Diamond
The Hope Diamond is a 45.52 carat, antique cushion cut, deep blue diamond of legendary beauty. Its origins are shrouded in mystery, but it is believed to have been cut down from a 112 carat diamond sold to King Louis XIV of France in 1668. That stone was cut down to 67 1/8 carats in 1673, and became an important part of the French Crown Jewels. It disappeared during the French Revolution and never resurfaced. The next reports of a lovely, large blue diamond occur in 1839, in the gem catalog of a collector named Henry Philip Hope -- the man from whom the Hope Diamond derives its name.