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Herkimer diamond is a double-terminated quartz crystal discovered within exposed outcrops of dolostone in and around Herkimer County, New York and the Mohawk River Valley. Because the first discovery sites were in the village of Middleville and in the city of Little Falls, respectively, the crystal is also known as a Middleville diamond or a Little Falls diamond.
| Herkimer Diamond crystals in a cavity|
Photo © Bill McIlquham
Many of the New York crystals are known for their extreme clarity, and Wiccan and New Age belief systems often ascribe specific occult properties and a wide variety of mystical powers to them.
These quartz crystals, which geologists theorize formed extremely slowly in small solution cavities or vugs, have 18 facets (6 sides) and two terminations. There are also larger cavities that are several feet in diameter that are called "pockets". Herkimer diamonds are found clear, cloudy, smoky or even containing a variety of rare impurities. Impurities (rare and general) can include clusters, scepters, fluid inclusions (sometimes incorrectly called enhydros), phantom, and bridge crystals. A fluid inclusion is a pocket within a crystal containing liquid, usually water, sometimes also methane or oil, and rarely, smaller crystals. A phantom is a crystal containing other visible crystals of the same type, a skeletal crystal contains a series of crystal edge outlines inside the crystal and a hopper crystal has its faces replaced by a step like pattern.
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