Best Website for Herkimer Diamond Information

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Free Website Where Herkimer Diamond Enthusiasts Share Information with the Public

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Dr.C. did two talks at the Herkimer Diamond Festival (July)which are in a Youtube movie. The research on the Herkimer District is in need of samples and photos.

How can you help? Visit the "how to help" page.

How were Herkimer diamonds made:
the Oil and Seed Crystal Theory

Over the decades that man has been collecting these shiny gems of the earth in the Herkimer district people have come up with many explanations as to how they got there.  Some of these older explanations are still on the internet and are discussed on the "old theories" web page.  This web page presents a new theory - the Oil and Seed Crystal Theory.

Any theory used to explain the origin of Herkimer diamonds must be a "best fit" to all of the evidence available.  On this website the "Oil and Seed Crystal Theory" is presented as the best fit.

Since 1999 there has been quite a bit of new science that sheds light on how Herkimer diamonds might have been formed.  In addition, we the community represented by have built a data base of observations that are supported by photographs.  The combination of the science and the field data has lead to a new theory, the Oil Migration and Seed Crystal Theory, which is presented here.

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 addition of holes to the rock is called increased porosity and it helped make space for Herkimer diamonds which were formed  after the host rock was formed. 
The host rock age is around 500 million years old, the minerals associated with Herkimer diamonds are younger - 300 to 400 million years old, but no firm dating has been done.  After the host rock was formed 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 into the flat "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 (and different types of fluid) resulting in hydrocarbon, 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 may 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?).

The short version : 1) the host rock is specially prepared with "holes" and made ready for the Herkimer diamonds, 2) fluids came into the rock along vertical faults and horizonal "hole layers" and made minerals before the Herkimer diamonds, 2) oil came into the rock which influenced Herkimer diamond formation (the oil part of the theory), 3) tiny Herkimer diamonds, called "baby floaters", came and acted as seed crystals (the seed crystal part of the theory) and then 4) the Herkimer diamonds grew where there was space and access to fluids.  Calcite formed after and much later weathering altered both the rock and the minerals. Click on Explanation above to see this short version illustrated.

There continues to be 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 (vug) with a couple, or a larger hole (pocket) 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 contributions every field season, we may 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:

W. David Hoisington, Ph.D.

 1. Snowball Earth - mass extinction and chemistry changes
There is a television show on snowball earth called "Prehistoric Disasters: Snowball Earth" -  a nice job talking about this event.
 2. Cambian Bloom - extensive stromatolite growth changing to  framework stromatolites with increased "holes"
 3. Limetone shelf and beach development (sand layers)
 4. Sea level changes and karst features and possible sabkha (coastal salt flats).  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.
During stages 7, 8 and 9 there are many pulses, or episodes, of mineralization. In addition there are pulses of hydrocarbons. The intensity of these episodes vary from one deposit to another and often can change within just one deposit.  But it is these two phases (#7 and #8) which result in the bulk of the different types of mineral specimens that come from the Herkimer district.  (Note: weathering, #10,  also contributes to variations in what a mineral specimen looks like).
 10. Migration Herkimer diamond fluids - Herkimer diamonds grew
 11. Migration of calcite formation fluids (and late sulphides)
 12. Faulting, erosion and more karst features forming open holes in the Herkimer host rock that sometimes are empty
 13.  The activity of man reveals the deposits.

Photo evidence of an early dolomite phase

Photos not available yet

Multiple druze episodes, see the photo evidence

See the quartz sphere page for evidence and the hydrocarbon page

Visit the calcite page and the sulfide page

No photos yet

Visit the hydrothermal page for more information

Note that there is a theoretical link between hydrocarbon and the formation of water clear Herkimer diamonds. Click on Questions at the top of this page

The above history is supported by scientific study (see the science page) and field evidence, including the mineral sequence (click on Other 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.  More photograph documentation, and specimen donation, is always welcomed.

The Herkimer diamond district is a unique area not just because of the Herkimer diamonds but also because of the fossilized oil field .  Information about both will help advance science in many ways.  The Herkimer district is a big place and the gathering of information needs to be done with the help of many.          This is a community project.

What probably happened across the 60 km long Herkimer mining district (map is on directions page - click Directions at the top of this 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  likely vary across the district.  The early cooler hydrocarbon fluids made an oil field which was then "fossilized" by the later, hotter, Herkimer diamond fluids.  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 (click on Other Minerals at the top of this page for a diagram), their direction of movement, and the timing of their effects upon each other, has contributed to a broad range of mineralization effects across the many Herkimer diamond deposits in the district. This is basically why each deposit is slightly different and also why variation occurs across a single deposit.

We do not have firm dates for when the above list of events happened, but we do know that the oil was there before the Herkimer diamonds and that the probable source rock for the oil is the Utica shale with an age around 450 million years.  Then you have to create the conditions for making oil from that shale and moving it into the Herkimer host rock.  In summary, the oil came into the rock long after it was made, maybe 100 million years after. But the possible age range for when Herkimer diamonds were made still falls within a large window from 250 to 450 million years ago.

There are many ways you can help with Herkimer diamond research.

You can help!
 Find out how.
 Click here

June, 2012

 9. The introduction of the "baby floater" stage and seed crystals from which Herkimer diamonds grew.

It is likely that during this pre-Herkimer diamond episode there was hydrothermal activity that altered the host rock.

Photo evidence to support the seed crystal theory

How Herkimer diamonds were made: The oil and seed crystal theory - a brief overview
 8. Migration of hydrocarbon  fluids - there were several episodes of this and at different times throughout the district. This is the oil part of the oil and seed crystal theory and it is important that the evidence indicates viscous hydrocarbons present BEFORE the development of Herkimer diamonds.

Art by Dr.C.