Herkimer Diamonds are in fact double-point quartz crystals.
These crystals are very clear and sport a natural faceting to boot!
Herkimer Diamonds get their name from the site where they have been discovered which is Herkimer County, New York. Other double-point quartz crystals can be found throughout the world but only those mined in Herkimer County, NY can be given the name "Herkimer diamond".
An awesome fact is how these crystals came to be formed: Their journey to become what they are now started around 495 million years ago... at the bottom of a shallow sea. Waxy organic material, quartz sand and large masses of pyrite encased by a rock formation made out of dolomite and calcite were slowly buried, leading to temperatures rising within it. The rise in temperature combined with cavities formed within the rock lead to these quartz being formed. The very slow process of the formation of the crystals aided in giving them amazing clarity.