Humans have been fascinated by gemstones for thousands of years. Today, gemstones are valuable not only for their beauty and rarity, but in what they can tell us about the earth and its history. In this high-interest video, the history, lore, and science of popular gemstones such as diamonds, sapphires, rubies, emeralds, and opals is explored. This video is one of the three part series NOVA: Treasures of the Earth: Gems, Metals
The allure of diamonds is far-reaching. The chemistry and crystal structure of diamonds is responsible for their amazing properties. Diamonds are the hardest known substance, yet they can be consumed in fire, or shattered by an accurately placed strike. The cutting of diamonds into eye-catching gemstones for jewelry is described. A dazzling diamond gemstone is the product of adherence to mathematical principles of crystallography and symmetry. The main factor dictating the brilliance of a diamond is the cut, which internally reflects all incoming light and directs its out towards the observer’s eye. The “fire”, or flash of colors within a diamond, results from the multiple refractions whereby incoming light is spread apart into its rainbow spectra of colors. The properties of carbon in the form of diamond, the hardest known mineral, and graphite, the soft material in pencil “lead”, are explained as the arrangement of carbon atoms in crystals that correspond to differing environments and pressures of formation.
The lore of diamonds is presented with New York, where the majority of America’s diamonds pass through, with Tiffany & Co., Marilyn Monroe, and the fabled Hope Diamond. The unique blue color of the Hope Diamond is derived from atoms of the element boron that are mixed into the diamond’s crystal lattice. The Hope Diamond is rumored to have a curse which afflicted its various owners. Today it resides safely within the Smithsonian Institute. The social costs of diamond mining are explored: The presence of “blood diamonds” on the market, diamonds that are sold via an underground economy that helps to bankroll dictatorial regimes in Africa; and the presence of horrific conditions in African diamond mines.
Along with diamonds, various other noteable gemstones are explored. We learn that sapphire and ruby are different colored varieties of the same mineral, corundum, the second hardest known mineral after diamond. Brilliant sapphires are mined from gravel in the island nation of Sri Lanka, where the famous 12-carat sapphire engagement ring stone worn by Princess Diana was obtained. In China, jade is valued above all other gemstones. Its characteristic green is seen in statues, armbands, and other types of jewelry. Its tough molecular structure led to it being associated with security; in Chinese lore, jade imparts a protective aura to its owner. In Australia, the multi-colored gemstone opal is called “the Queen”. The diverse colors of opal is derived from its physical structure, billions of tiny spheres of quartz suspended in a geometric array. The world’s largest brilliant green emeralds are found in North Carolina, the gift of an ancient continental collision that created the Appalachian Mountains.
Gemstones form in various ways. Many are related to the motion of earth’s plates, what we call plate tectonics. Volcanic activity deep in the mantle creates diamonds, which form on an upwelling plume of magma termed a kimberlite pipe. Inclusions of ancient material in diamonds also reveals that plate tectonics likely started about 3.2 billion years ago. Sapphires and rubies form when one of earth’s plates subducts or pushes its way under another plate. Australian opal appears to be derived from water-borne silica which is precipitated in fissures and cracks in the earth; opal can even replace the shapes of once-living life creating amazing opalized fossils. Although technically not a crystal, opal appears under the electron microscope as a fantastic congeries of tiny, perfect spheres of silica.
The PDF contains a two-sided video worksheet consisting of 50 multiple choice and true-or-false questions, along with an answer key, and an MS Word download link. You will need to obtain a DVD of the video, use the PBS Internet site, or YouTube