10.9" Plate of HUGE Herkimer Diamonds on Sparkling, Druzy Quartz

Herkimer diamonds are not actual diamonds, but rather double terminated quartz crystals found in and around Herkimer County, NY. The diamond in the name is from not only their exceptional clarity, but also from the natural facets they display when found. Only crystals with these qualities found in Herkimer County, New York can be called "Herkimer Diamonds". Similar double terminated quartz crystals have also been found in abundance in Tibet and Afghanistan, but these are not true Herkimer Diamonds.

The geologic history of these crystals began 495 million years ago in a shallow sea. Waxy organic material along with quartz sand and pyrite was encased in rock made of dolomite and calcite. As sediment buried the rock and temperatures rose, crystals grew very slowly, resulting in quartz crystals of exceptional clarity. Inclusions can be found in these crystals that provide clues to the origins of the Herkimer diamonds: solids, liquids (salt water or petroleum), gases (most often carbon dioxide), two- and three-phase inclusions, and negative (uniaxial) crystals.

Quartz is the name given to silicon dioxide (SiO2) and is the second most abundant mineral in the Earth's crust. Quartz crystals generally grow in silica-rich environments--usually igneous rocks or hydrothermal environments like geothermal waters--at temperatures between 100°C and 450°C, and usually under very high pressure. In either case, crystals will precipitate as temperatures cool, just as ice gradually forms when water freezes. Quartz veins are formed when open fissures are filled with hot water during the closing stages of mountain formation: these veins can be hundreds of millions of years old.