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The best website on "Herkimer Diamonds"
There are some questions about Herkimer diamonds that are asked with regularity. For example: Why are they so clear? What is listed here are those questions that people have sent by email to this site, or have mentioned on the community page, or mentioned in conversation. It is important for the viewer to understand that answers to these questions are based on theory. Most answers given will be linked to a theory about how Herkimer diamonds are formed, and the science in support of that theory. One of the main functions of this public website is to keep the theory up-to-date and scientifically supported (see the New Theory page). Science is always pushed forward by inquiring minds and we are always open to questions, ideas and comments. Please send us your comments and questions using the community site.
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FAQ - Frequently Asked Questions about Herkimer Diamonds
A public service project always open to input from the community interested in Herkimer diamonds.
Web page author - W. David Hoisington, Ph.D.
Why are Herkimer diamonds here in New York?
Why are Herkimer Diamonds so clear?
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There is a simple answer to this. This place is where a unique set of geologic conditions occurred in this location (Herkimer county, NY) that have not occurred anywhere else in the world. These are briefly listed on the theory page (click new theory link at the top of this page) and understanding how these features combined to help make the Herkimer district is the more complex answer.
There are other locations that produce small quartz crystals with a similar form, but there is no other location in the world that has the range of features found in the Herkimer district.
This is not an easy question to answer and there really has not been research applicable to this until recently. What is observed in the field is that there is a correlation between very clear crystals and black carbon material, hydrocarbon. The theory suggests that this hydrocarbon is the residue from oil. In addition field evidence, in the form of skeletal crystals, suggests that the fluid related to the formation of Herkimer Diamonds was at times chemically super-saturated with SiO2 and that there were sharp fluctuations in this availability and nature of this fluid (see discussion on the skeletal page). There is also evidence of this solution flucuation in the varied forms that quartz takes throughout the Herkimer District. When such dramatic flucuations occur impurities are likely to occur within the crystal because of changes in the rate at which the crystal faces grow. If the crystal can grow at a constant steady rate despite the fluid/chemical fluctuations then it can result in a clear crystal (provided there are no other impurities in the solution like hydrocarbon flakes and bubbles). This steady state crystal growing process is aided by the presence of hydrocarbons (oil/gas) in the solution during the Herkimer diamond growing process, thus the link between the black carbon material and the clear crystals.
There appears to be a size maximum for very clear crystals - about 5 cm point to point, and more commonly 3 cm. This again is probably related to solution impurities and fluctuations having more time/volume to cause an effect when the crystal is larger.
In addition, it is important to consider the effect of freeze-thaw. Any crystal that is exposed to water that freezes in winter can develop fractures. The open holes that contain Herkimer diamonds, in particular the larger pockets, can be an avenue for water movement and thus prone to the freeze-thaw action. The pockets packed with carbon might be less prone.
There seems to confusion about this in regard to the smoky color found in the occassional Herkimer diamond. There is some folklore suggesting that the smoky color is due to micro amounts of carbon matter in the crystal. In actuality this is a correct answer only for BLACK quartz from the district (not smoky). The smoky quartz is actually caused by radiation bombardment from a small amount of uranium that has accomanied some of the hydrocarbon material, but not all of it (and why all of the quartz is not smoky).
Another common notion is that there is an Aluminum impurity involved. Although this might be true for smokey quartz in granitic terrain (like the Conway granite of NH) is it probably not true in the Herkimer mining district. Here, in the absence of aluminum bearing rocks like granite, it is more likely that an OH bond is being effected, both in making the smoky color and in color healing processes (changing back to clear/white - which doesn't happen as freely with the Aluminum variety).
Wating to answer your question.
How come some of the Herkimer diamonds are smokey?
Some people may desire more scientific information regarding the formation of smoky quartz. Below is a short pdf document. BEWARE! This document has very scientific information and can be difficult to understand.
More information about smoky color is on the science page - click science at the top of this page.
Why are they called Herkimer diamonds?
This more of a historical answer than a geological one. They are named after General Herkimer and the "diamond" term was given to enhance their marketting, due to their clarity and bright sparkle. But the name "Herkimer diamond" is not an official quartz variety name (like the name amethyst). Thus far there is no research to indicate that the quartz from Herkimer county is chemically or morphologically unique. But the lack of science doesn't change the popularity of the name and its widespread use.
Although other locations that produce small quartz crystals with a similar form, the name Herkimer diamond should be applied only to those quartz crystals found in the Herkimer district. But there are a wide range of quartz habits in the Herkimer district. Is every type of quartz to be called "herkimer diamond"? If not what are the parameters to use that will say this one is a Herkimer diamond and this other is not?
Go to the Herkimer color page to see photos of smoky color