Herkimer diamonds are a unique form of quartz crystal found in the Mohawk River in Herkimer County, New York. They are mostly brilliant, very clear and show the classic 18-sided, doubly terminated hexagonal form. When there are inclusions of water, carbon, etc., these provide clues to the exact origins of the Herkimer diamonds.
The very intriguing geological history of Herkimer diamonds dates back to approximately 500 million years ago. Organic materials along with quartz, sand and pyrite were encased in rock. Temperatures rose as sediments buried the rock causing the organic material to decay. The result was a gas, that when trapped, reverted back to a stone state. Finally, over the course of 300 million years, the glaciers that sat atop Herkimer County began to melt, and washed away layers of the sedimentary rock, allowing the compounds and elements inside these pockets to cool down and crystallize. This whole process causes the quartz to come out of the solution very slowly and results in the growth of quartz crystals of exceptional clarity.