This site was last updated on May, 2011
Scientific Information Related to Herkimer Deposits
Definitions and Scope:
The best website about "Herkimer Diamonds"
This part of the website will have links to scientific information that is, or at least hypothetically might be, linked to the formation of Herkimer Diamond deposits. Most of the information posted here is quite scientific and may not be easily understood by the general public. There will be comments posted by the author of this website (in white lettering) that proposes the connections of the information to the Herkimer Diamond deposits. Additional comments are welcome - just use the email or the community page.
"Snowball" Earth - The Land Before 500 Milion Years:
Stromatolites and Other Cambrian Carbonate Fossils:
Karst Development & Solution Breccias - Openings in the Rock:
Carbon Cycle and Carbonate Platform Development:
Cambrian Earth - What was it like 500 million years ago?:
The Host Rocks for the Herkimer Diamond Deposits:
Quartz Crystal Growth - Why are Herkimer diamonds so clear? The link to Hydrocarbon:
The Dolomite Debate:
Anthraxolite or Something Else? Let's call it hydrocarbon!
TBR Gas Play in Cambrian Carbonates - A comparison to Herkimer:
MVT Deposits in Cambrian Carbonates - A comparison to the Herkimer District?:
The Post-Cambrian Tectonic History - "Earthquakes":
Age Information on Some Mineral Deposits in the Applachians:
New York Geology and Regional Geology Information:
Mentions "large growth-framework cavities, as well as metre-sized caverns", a definate increase in porosity tied directly to the reef.
Includes comments on the carbon cycle
There are "desication cracks and intraclasts indicative of tidal flat (peritidal) deposition". This, and sea level changes, says a lot about the conditions where the Herkimer host rocks were formed. It was shallow and close to land.
Also see below - karst development and sea level changes
Similar porosity changes may have happened in the Herkimer region
In the Herkimer deposits field evidence shows there are clearly 2 calcite crystal phases after dolomite, and a third (in some places).
There appears to be evidence that dramatic sea level changes took place, several times, during the time the Herkimer host rocks were being formed and directly after. This would have significant effects on the host rocks , first in creating interlayered sand deposits and secondly in creating creating solution openings and breccias (weathered broken rock as fragments), both are evident in Herkimer depositis, and in other similar rocks in the Eastern USA. There are ever "dry holes" in some of the Herkimer deposits with nothing in them. Both of these events (sand layers and solution openings) helped to increase the porosity of the rock and aid in helping fluids to flow through. This increased porosity helped to make room for the formation of the Herkimer diamond deposits, and in some instances quite large openings that could be filled with crystals.
There is a stromatolite layer associated with most if not all of the Herkimer Deposits. It is likely that during this late time in the Cambrian, and this close to land, the stromatolites were becoming what are called the "framework" type. If that is true then the rock they helped to make (the Herkimer host rock) also likely had a greater porosity and may have even had visible open spaces. This increased porosity helped to make room for several events of fluid flow through the rock and helped in the formation of Herkimer diamond deposits.
This idea of stable continental boundaries (in relative motion to each other) alows the sea floor to remain stable, and to have a shallow sea for an extended period of time helping to establish the stromatolite boom.
Probably the most important point to consider here is that the Herkimer host rock environment, at the time is was being formed, was not conducive to preserving organic carbon. Most of the carbon was used in making carbonate (limestone) and feeding other animals (there may have been worms and other burrowing animals - see next section below). Then if there was any organic material left after that it was likely washed out to sea, due to the fact that the Herkimer host rocks were formed quite close to land with both river and beach activity.
We can never really know what happened 500 million years ago. What we can do is take all the pieces of information and present a model, or hypothesis, that's the best explanation, one including all the information and all the field evidence. The field evidence from the Herkimer deposits is mostly located on other pages within this site. What is located on this page is the scientific information about the behavior of the rocks and the fluids which might have influenced the formation of Herkimer Diamonds. The scientific information below is divided into topics (light blue headings) and includes links for more details (white blocks).
There are many different things we can say about geologic history just prior to the Cambrian (Herkimer host rock time), but one of the most important would be that almost all life perished. This then left little competition for the stromatolites that followed in the Cambrian It is also likely that there were some effects to water chenistry due to distant, but massive volcanic eruptions. This, along with the glacier event, may have scraped the earth bare (leaving behind glacial erosional features) and poured acid rain on it, thus changing the nature of rock erosion.
When considering the role that the Herkimer host rocks played in assisting Herkmier diamonds to be made, it is important to consider the entire history of the rock. This means the conditions on the Earth before it was formed, while it was being formed and after it was formed (all the points discussed above). Then, if we have proper evidence, we can place the timing of when the Herkimer diamonds grew somewhere within that total historical framework describing Herkimer host rocks as they appear today. It includes all the information on this "scientific" page, plus the field evidence. The linking together of all this information in a "story" about the history of Herkimer diamond deposits is done on the the new theory page.
There was quite a bit of past "earthquake" activity in the Herkimer region. A fault in Little Falls is reported to have had a "throw", earth movement, of 800 feet. There were several differernt episodes when the earth was either cracking apart (called extensional faulting) or being squeezed (called compressional faulting). It appears that field evidence supports a relationship between fault development and the occurence of extensive mineralization. The fauts occured some time after the host rocks were formed. This also means that the mineralization events are much younger than 500 million years.
What is important to note is that the Herkimer region (district) is at the the intersection of two major (tens of miles long) fault trends - one basically North-South and the other basically East-West (thanks to Taury Smith from the NY State Museum for this info). This has likely added another unique feature to the Herkimer host rock - well developed intersecting sets of jointing, or what is observed in the field as breaking into nice blocks. This joint pattern also affected rock porosity and the flow of mineral fluids. It is likely that the regular distribution of Herimer diamond pockets along a layer is in part due to the increased porosity at intersecting joints. In the 1960's collectors would probe the joints with a metal rod until they heard a certain sound. The sound of hitting a Herkimer diamond. Following well developed joints (in addition to understanding the distribution of crystal bearing layers) can still be used today in prospecting for Herkimer diamond "pockets".
There are videos that contain much of the information on this page ->
The website above is an important piece of research that indicates mineralization episodes occurred before and after the Herkimer diamonds. This is similar to the field evidence in the Herkimer deposits (see minerals link at the top of the page). In addition the researchers suggest that the Herkimer diamonds and the anthraxolite are linked, and also tied to petroleum bearing fluids, about 200 degrees C. In the next section on quartz growth we will see the importance of this temerature. In addition these are fluids which came into the host rock considerably after the rocks were formed, perhaps as young as Permian (290 million years old). This younger date is similar to other mineral deposits in the Applachians and similar to mineralization in Cambrian rocks elsewhere in the USA (scroll down to see supporting information).
The gas deposits in the Finger Lakes region of NY are hosted in rocks very similar to the Herkimer host rocks. The study done at Palatine Bridge, which is within the Herkimer region, suggests a similarity between the fault related mineralization found there and the mineralization associated with the gas deposits. This is supportive evidence suggestive (along with the "anthraxolite") that petroleum bearing fluids moved through these Herkimer host rocks rocks after they were fractured by faults. The petroleum bearing fluids are directly linked to the formation of Herkimer diamonds (along with all the conditions that created dramatic increases in porosity). Additional studies in both the gas deposits and in the Herkimer deposits may help scientists to understand both.
The article above points to the importance of "extensional faults", or cracks that open instead of close, as important to the movement of mineralization fluids. This is consistent with the inofrmation gathered by other reasearchers. But there is some conflict about the date of mineralization (their's being the end of the Taconic Orogony, or about 430 million years old). But there was intense extension during the Permian throughout the Appalacians and several quartz rich mineralization episodes in NY are dated to that time. Another researcher suggests that mineralization episodes occurred throughout the tectonic history of the region (see article below).
Could it be that younger tectonic events (Permian - 290 million) have had a role to play in forming these gas deposits and some of the associated mineralization? It would fit better into the regional picture, and what we know about the need for deep organic rich basins. In addition other researchers point out the importance of "younger tectonic fracturing" in the formation of productive, carbonate hosted, gas and oil deposits throughout the world (see below). Open "extensional" cracks are VERY important not only in the oil and gas deposits but also the Herkimer Deposits.
Dolomite is an ever present mineral in the Herkimer diamond deposits. The host rock is called the Little Falls dolostone - a stone made of mostly dolomite. Dolostone was originally limestone and then the calcite in the limestone was changed to dolomite with the addition of magnesium. There is a scientific debate about how dolomite is formed and basically there are two sides to the argument: 1) the fluids that made the dolomite were there with the burial of the rocks, and 2) the fluids were introduced later along faults and rock layers with good porosity (lots of holes/cracks).
Or another article (that also describes mineralization similar to the Herkimer area, see below) which suggests post-Taconic extensional faulting (the opening of the rocks) with mineralization "can be consistant with being far field effects of Paleozoic and Mesozoic tectonism" or younger than Taconic and more consitent with regional mineraization.
It is likely that the Herkimer region has the same combination of hydrocarbon deposits and mineral deposits found elsewhere in the USA and in the world. Here in NY we have TBR gas deposits in the Finger Lakes area and "signs" of MVT deposits in the Herkimer region. A familiar pattern, which is something nature tends to do. These MVT signs include 1) a zinc mine, 2) well formed chalcopyrite in the Hanson/Benchmark quarry and 3) reports of galena and sphalerite in the region. Although the Herkimer region does not contain economic concentrations of metals, it is a "mineral district", or a region of hundreds of square miles that has similar mineralogy. That is also similar to MVT deposits. The Herkimer host rock is also similar (see info on the Viburnum Trend). The Herkimer district also has some similar mineral deposition patterns, and the associated gas deposits have a similar "geochemical signature" (see article below).
Evidence for "framework" structure and open spaces
What can be added to this list of interesting deposits is the appearance of chalcopyrite and sphalerite in the Hanson/Benchmark quarry (with Herkimer diamonds) and the fact that there is a zinc mine (not commercial) within the Herkimer District. Neither of these two deposits have been dated but they have characteristics that are similar to other MVT deposits AND, as such, they could fit into a younger time frame of formation (340 to 240 million years old) consistent with the regional mineralization picture.
Note: A comparison is being made in this scientific analysis between Herkimer deposits, TBR gas/oil deposits and MVT deposits. The ages of which are discussed above. Additional ages on mineral deposits can support this analysis.
Probably one of the most frequently asked questions about Herkimer diamonds is "It looks like it was cut. Was it formed like that? How did that happen?" What is presented here is some evidence and some ideas that answer these questions.
The link between hydrocarbon and clear Herkimer diamonds is well established in the field. Large pockets can be filled with hydrocarbon (sometimes with clay too) and contain hundreds of clear crystals. These have been nick-named "Jewery Boxes". Below is a discussion of the importance of this link with carbon (or hydrocarbon) as a controlling factor in the formation of clear Herkimer diamonds.
The Carboniferous time period, with the large amount of preserved carbon in its rocks, is well known to be linked, as a source, to gas and oil deposits throughout the world. Such a consideration should be given to the TBR gas deposits in the Finger Lakes area. A post, or late, Carboniferous date for the Herkimer deposits would be consitent with the scientific information presented here.
An interesting piece of research that looks at dark quartz containing carbon inclusions from Nevada and the Herkimer area. The main focus was to see if the element C (carbon) was fitting into the quartz (formula = SiO2) structure. It was not. But the study did show that Herkimer diamonds with black inclusions contained carbon with free radicals. It was concluded that the dark color of the "smokey" crystals were due to the carbon, which has led to a false rumor in the field that all "smokey" Herkimer diamonds are caused this way. There is a difference between black and smokey. It is likely that some of the carbon material (not all) contained uranium (another research paper discussed finding platinum in anthraxolite at Fonda, see link below). There is also an old paper showing the occurrence of uranium with anthraxolite ( see link below ).The link between uranium and organic material is fairly common. It is the radiation from the uranium in some carbon that causes the occassional smokey color. But black quartz is due to carbon inclusions or coatings.
This research should be exciting as it is an attempt to grow laboratory quartz in the presence of hydrocarbons and to see if Herkimer diamonds can be duplicated. The theory being tested is based on the premise that hydrocarbons (petroleum fluids) were present during the formation of Herkimer diamonds and that these fluids had a significant impact on the crystal growth - basically acting as a growth rate inhibitor. A slow rate of growth helps make clear crystals by moderating the impact of imperfections, particularly those due to dramatic changes in solution chemistry.
There is other research to suggest that quartz crystalization, at temperatures around 250 degrees C (close to the temerature established in the anthraxolite research above), is stablized in the presence of hydrocarbon fluids. Rapid fluctuations in the quartz saturation of the solution (how much quartz is disolved in solution) would normally change crystal growth rates, but with the hydrocarbons present the growth rates remain constant across changes in solution concentrations (see field evidence discussion below). What this means is that crystals can grow at a smooth and constant rate and will have less imperfections even with changes in the quartz concentrtaion of the fluids flowing through the rock. This means the crystals are more likely to be formed clear.
There is field evidence that solution concentrations did vary. The occurrence of "skeletal" or "hopper" crystals is an indication of supersaturated fluids. Many skeletal features show "melting" and "healing" textures indicating another change in the solution concentration (including skeletal contacts but no visible features in the crystal, and "phantom" crystals - faint outlines of crystals inside crystals). Finally there are crystals that show no skeletal features. For photos of these features go to the crystal form page or the skeltal page.
Field evidence as support for solution concentration changes
In addition to the above super saturation changes it is important to note that there is evidence of several diferent episodes of quartz mineralization within the Herkimer deposits. Before the Hekimer episode, there was a "druze" episode (probably several, again illustrating saturation variations) anfd the crystals are pyramidal and not Herkimer like. And proposed here is a new term called "baby floater druze". This is a unique druze like coating of microscopic, totally clear, Herkimer diamonds. These "baby floaters are also found inside (locally called "manifestations") some of the best clear Herkimer diamonds. There is often an association between large clear crystals and "baby floaters". Sometimes the "baby floaters" stick out of the larger crystal, or leave a contact imprint (not a skeletal contact), or are partially "melted" back into the larger crystal leaving a ghost. All of this is evidence of "true floaters", which are Herkimer diamonds not attached and may have even crystalized "floating" inside hydrocarbon.
Note: As stated above, there is field evidence that both disolving and growing of quartz crystals was likely occuring in the Herkimer deposits which is best seen in the hopper crystals - see the skeletal page
The Cambrian was a unique time in Earth's history. There was a stromatolite bloom followed by the arrival of a wide diversity of creatures unknown to us today (see info on the Burgess Shale). But what was likely the most important in terms of the Herkimer diamond deposits was that conditions were just right for making a rock that would be porous enough (had holes and cracks) for mineral bearing fluids to move through. This is the significance of the shallow sea, the carbonate platform (with porous limestone), the later karst (cave like processes) events, and the later fault and fracture events. They all combine to make a unique set of conditions to help for the region (district) of Herkimer deposits.
What is not known is the relationship between the "baby floaters" and the formation clear Herkimer diamonds. As a "old time" collector, I can say that if someone shows me a 1 to 2 inch very clear Herkimer diamond that has a brilliant sheen, almost irridescent, on its faces, then there is a strong probability it comes from a pocket with "baby floaters". Exactly what that means is yet to be determined. It does not mean that all clear crystals are associated with "baby floaters". But all this information will be woven into the new theory describing how Herkimer diamonds were formed.
The above research suggests that the black carbon in the deposits (anthraxolite, bitumen or pyrobitumen) was at one time fluid hydrocarbon. The research also draws parallels between mineralization in the Herkimer region and mineralization in TBR gas deposits within the Finger Lakes area. Both types of deposits are hosted in similar rocks with similar mineral deposition histories. It seems that oil exploration geologists looking for TBR type oil/gas deposits also look for MVT (Mississippi Valley Type) deposits in the same region as evidence of fliuid flow through the rocks - a common association in other regions.
MVT deposits have younger dates than those given to Herkimer deposits*
Several researchers have pointed out that fluid flow associated with mineralization is related to fault structures - both in the Herkimer region and in the TBR deposits (see above research). Tectonics have also infuenced the MVT deposits (see below). This is another similarity.
As we can use the study of the TBR deposits in NY to learn something about Herkimer deposits, we can also look at research done on Cambrian hosted MVT deposits. Perhaps we can find within this research ideas that point us in the direction of long unanswered questions about the Herkimer deposits. One question is "Why are there different layers of mineralization?" A possible answer - there were changes in the rock porosity.
Most of the MVT deposits have dates younger than those attributed to the Herkimer deposits. It is suggested here that there was a regional mineralization event in PA-NY that has similar, and earlier, dates to the MVT deposits. More evidence to support this is cited below. Part of this research project is aimed at better dating of the Herkimer deposits.
IMPORTANT RESEARCH PAPER
If you are an "old timer" and experienced in finding Herkimer diamonds then you know of the connection between Herkimer diamond deposits and "black carbon like material" which some have called anthraxolite. It has also been called bitumen, pyrobitumen, hydrocarbon and in the past it has been connected to coal making processes. There has been a "black substance" from the Hanson quarry that reportedly smelled like "gasoline". Perhaps there are many variations in this "black carbon" looking material. There may be some confusion as to what name to apply but any theory explaining the formation of Herkimer diamonds MUST explain the formation of, and role of, the carbon material in connection to clear crystals.
Above is an interesting article that looks at the distribution of fossils in rocks that are of similar age to the Herkimer host rocks across a broad region. An important part of the paper speaks of an "unconformity" over the Herkimer host rocks. This a discontinous gap between rock layers indicating that the Herkimer host rocks were exposed to weathering and erosion AND that this was an event specific to certain areas (all of the Herkimer region) and not found in other areas. What happened at that time was that a karst environment was formed, a time where the limestone was having small "caves" made in it. That changed the Herkimer host rocks making them even more open (porous) to fluid movement and ready to host the Herkimer diamonds..
The above study was done in the Little Falls area looking at faults and associated fault networks and the distribution of dolomitization (how much of the limestone was turned into dolomite). What was found was that mineralization was connected to "all fracture sets host veins except N-striking ones" (see the above paper). The research also showed that there were several episodes of mineralization (similar to our crystal field evidence, click on minerals link at the top of the page) and that there was a similarity to observations in nearby gas deposits see below). The above study did show that were mineraization events occuring at different times, some earlier than others. Perhaps there was also a change in the fluid chemistry at different times.
It is anticipated that we will add a photo page that has side-by-side photos of mineralization from MVT deposits and mineralization for the Herkimer region (district) . Click on the link.
A public service project always open to input from the community interested in Herkimer diamonds.
There has been liquid oil and bitumen found with some fluid inclusions inside Herkimer diamonds. The oil is a yellowish/brownish color (go to inclusion page and also scan down to see inclusions of an amber colored material). A sphere of of hydrocarbon material was found (go to carbon page) and spheres of quartz that most likely were formed inside gas bubbles (go to sphere page).
Given this to be factual field evidence then it may be that the change from liquid hydrocarbons to solid residue (degradation) was variable across the entire Herkimer district (the paper cited below shows that this variable oil degradation is a common phenomenon) and thus this may actually have resulted in a variety of "black carbon" substances (and a variety of names). Using the term hydrocarbon would include all the possible varieties and is a more appropriate term than anthraxolite.
New information will be added to this page as researchers are currently seeking information to questions about the formation of Herkimer diamonds. To see this ongoing research go to the new research page.
Click on the Link
Much of the karst research calls into play the role soil development in connection to acids that leach away the carbonate. 500 million years ago the soil would have been quite different.
Web page author - W. David Hoisington, Ph.D.
A discussion of the chemical analyses and issues
What probably happened across the 60 km long Herkimer mining district is that there were various "pulses" of early mineral fluids, followed by pulses of oil/gas. The intensity of these pulses would likely vary across the district. Following, and maybe overlapping the late oil/gas pulse, was the Herkimer diamond fluid pulse. This pulse contributed to variable oil degradation throughout the district. The changes in the intensity of these various pulses, 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.
*Note that we do not have a firm date for the mineralization in the Herkimer District. Only a date based on the host rock.
Please note that there is a difference in age between the host rock and the formation of Herkimer diamonds.