This site was last updated on May, 2011
New Theory of How Herkimer Deposits Formed
The best website on "Herkimer Diamonds"
The new theory about how Herkimer diamond deposits were formed is based on the field evidence (see the three links below) and on the scientific evidence (see the science page). The new theory will seek to combine these sources of information together into a theory that best explains all the observed field evidence and answers the questions posed by Herkimer enthusiasts. In addition we hope to convey this explanation of how the Herkimer diamond deposits were formed in a format that is easy to understand by the general public and yet also supported but the best scientific knowledge available.
"A unique mineral deposit requires a unique set of conditions"
A public service project always open to input from the community interested in Herkimer diamonds.
Links to pages containing field evidence and photos
If you don't agree with the above theory and have information to support a better theory then please send it by email. Science is always open to new ideas and information. If you have seen something in the field, if you have an "odd" specimen, then please send us an email. Odd things are usually great clues!
The development of this new theory is also tied to new research projects. See the new research page
Web page author - W. David Hoisington, Ph.D.
A Really Brief History of Herkimer Diamonds by W. David Hoisington, Ph.D.
Many theories and ideas have been tossed out there to explain how Herkimer diamonds were formed (see old theories page). What is proposed here is a new theory that better fits all the field and laboratory evidence. It is a work in progress, as more evidence is currently being collected.
Herkimer diamonds are found in Herkimer county, New York. They are very shiny quartz crystals that are doubly terminated (coming to a point at both ends of the crystal) and at first look they shine like a diamond. There are many places outside of New York that claim to have Herkimer diamonds, but they are mislabeled. Herkimer diamonds come from only one place in the world.
Over the course of Earth's history this place in New York was the location for a unique sequence of overlapping of events. This unique sequence of events started around 500 million years near an ancient shoreline. Over millions of years sedimentary rocks were formed at this shoreline and they had open holes along certain layers. These holes were formed due to a combination of weathering and stromatolite (ancient fossils) features. This is called increased porosity - which formed avenues for later fluids to follow.
Sometime after the host rock was formed (300 to 400 million years ago, but no firm dating has been done), deep within the Earth, fluids containing gas, oil (leaving behind "black hydrocarbon material"), salt and dissolved quartz (and a few other things) moved up along cracks (vertical flow) and then out along these porous layers that had all the holes (horizontal flow). As the fluids moved into the cracks and the "hole layers" the solutions eroded the holes further, and also provided material that helped to "grow" the doubly terminated quartz crystals called Herkimer diamonds. There were several episodes (see the mineral sequence diagram) of this fluid movement resulting in different minerals and different types of quartz. These episodes also vary slightly from one deposit to another and this gives rise to some features that are unique to only one deposit. In adddition variations in the effects of vertical fluid movement versus horizontal fluid movement add to the unique features seen at each Herkimer diamond mine. Some mines mat have had mostly horizontal flow (like AD and CG) and others have mostly vertical (like HBQ) and many show effects of both (like DA, TCR and TM?).
There has also been additional groundwater movement through the "hole layers" that has resulted in changes (etching, erosion, weathering, pocket collapse) to the cavities containing the Herkimer diamonds. Today you can crack open the rock and find a hole with a couple, or a larger hole with a hundred, Herkimer diamonds inside, and then there are empty holes with smooth weathered walls.
This is a really brief history and the details are more complex and varied across all the different deposits in what is called the "Herkimer Diamond Mining District" (or just Herkimer district). More detailed deposit paragenesis (history) for every mine will be presented in the future, after more information is collected. With the help of many hands making contributions every field season, we are hopefull to put more pieces of the puzzle together.
The Herkimer district hosts a unique mineral formation and as such requires a unique set of conditions, or history. This history is proposed below:
1. Snowball Earth - mass extinction and chemistry changes
2. Cambian Bloom - extensive stromatolites changing to framework stromatolites with increased "holes"
3. Limetone shelf and beach development (sand layers)
4. Sea level changes and karst features - increased "holes"
5. Early dolomite formation? Near surface?
6. Burial and formation of adjacent organic bearing sediment basin, collapse of earlier karst features and the open stromatolites. "Hole bearing" layers adjacent to sandy layers - forming porus channel ways ready for fluid migration.
7. Faulting, migration of early silica fluids (druze phase) along previously formed porus channel ways, also early hydrocarbon.
8. Migration of Herkimer diamond fluids with hydrocarbon
10. Faulting, erosion and more karst features forming open holes in the Herkimer host rock that sometimes are empty
9. Migration of calcite formation fluids (and late sulphides)
Also visit the carbon page for additional discussion
11. The activity of man reveals the deposits.
The above history is supported by scientific study (see the science page - click on science at the top of this page) and field evidence, including the mineral sequence (click on minerals at the top of the page). Yet it is a "hypothesis", a theory under investigation. Information is added regularly and contributions of information are warmly welcomed.
There is a television show on snowball earth called "Prehistoric Disasters: Snowball Earth" - a nice job talking about this event.
After the early druze episode and the early hydrocarbon episode there is a later druze phase followed by a strong hydrocarbon phase and then the Herkimer diamond mineralization. The intensity of these mineral phases varies from one deposit to another and often varies within just one deposit. But it is these phases (#7 and #8) which result in the bulk of the diferent types of mineral specimens. (Note: weathering, #10, also contributes to variations in what a mineral specimen looks like).
This theory, with all the supportive documentation on this website, is not published elsewhere. Please reference the author, date (top of the page), and the website.
Note that there is a theoretical link between hydrocarbons and the formation of water clear Herkimer diamonds.
What probably happened across the 60 km long Herkimer mining district (map on home page) is that there were various "pulses" of early mineral fluids, followed by pulses of oil/gas followed by, and overlapping the fluid pulses that made the Herkimer diamonds. The intensity of these pulses would likely vary across the district. In addition there are vertical flow features (movement up cracks) and horizontal flow features (movement along porus beds). The changes in the intensity of these various pulses, their direction of movement, and the timing of their effects upon each other, has contributed to a range of mineralization effects across the many Herkimer diamond deposits in the district. This is basically why each deposit is slightly different.
Please note that there is a difference in age between the host rock and the formation of Herkimer diamonds.
