Herkimer Diamonds can only be found in one place in the world, Herkimer County, New York, USA.  They are very unique in that they come out of the ground double terminated with 18 faces (naturally faceted). A common diamond must be formed by a lapidary in order to appear terminated and faceted in this way.  Herkimer Diamonds are a quartz crystal.  Most quartz crystals are a 7 on the Mohs hardness scale while Herkimer Diamonds are 7.5.  They are more rare than a common diamond and are over 500 million years old. Many Herkimer Diamonds can be found to have black spots in them.  This is called Anthraxolite, black carbon deposit which looks similar to black coal.  Some even have bubbles of water found in them or a rare combination of the two.  Your Herkimer Diamond can be valued based color, clarity, and carat weight