This site was last updated on July, 2010
The best website on "Herkimer Diamonds"
Almost all the pockets containing clusters of Herkimer diamonds come with a black carbon material, most appropriately called hydrocarbon, along with clay (mud). Even some of the small "vugs" that have only one or two crystals may be packed with the black hydrocarbon. There is an association of clear crystals with the hydrocarbon rich pockets, as opposed to the more mud filled ones. Below is a picture donated from Bill and Anne where you can clearly see all the black with the herkimer diamonds. To the left is a microscope picture of the typical hydrocarbon on first phase dolomite (Fonda, NY - DA, 2008). You can see the curved shapes it commonly makes as well as the dimpled texture. But the black material takes many forms and calling them all "anthraxolite" may not exactly be accurate. Yet they probably are all forms of degraded oil, or hydrocarbon.
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Other Minerals - Clay and Hydrocarbon
A public service project always open to input from the community interested in Herkimer diamonds.
In the scientific section, rationale is given for using the term "hydrocarbon" as opposed to the name anthraxolite. The rationale is that this material is most likely "degraded oil", which simply means that it is oil which has lost most of its lighter components. But there is evidence in the Herkimer district that this hydrocarbon occurs in a wide variety of forms. Although the above form is most common, it has been seen as a light dust over druze (at Middleville, HD), as dust inside septer rods (Little Falls - TM, St. Johnsville - HBQ), and as film coatings on phantom prismatic quartz crystals that sometimes appears more brown than black (St. Johnsville, HBQ). This is shown below:
And in some instances a golden brown fluid can be found as an inclusion, which is most likely oil. Click here to go to the inclusion page to see a photo ->
Hydrocarbon, smelling like "gasoline" mixed with sulfur, has been reported from St. Johnsville (HBQ) and oil has been found as inclusions in Herkimer diamonds. In addition hydrocarbon has been seen as a fine dust, as a fine sand and as round spheres (see photo below). Combine this with the photographic evidence above and this means there is evidence that all the black carbon material found in the Herkimer district may not be the same. This is because it is probable that the oil which came with (and before) the mineral forming fluids arrived at different times and "degraded" differently at different locations in the district and even within a single deposit. Giving all the black material the same name of "anthraxolite" may be faulty unless it is actually determined to be that through some form of analysis. This makes little difference in terms of collecting Herkimer diamonds, but it does make a difference in terms of developing a theory explaining their history. In addition, the variations in the occurrence of the hydrocarbons, in connection with variations in the timing and intensity of the various quartz episodes, may help in explaining most of the differences that are seen from one deposit to another (see mineral sequence diagrams).
Some of the "pocket" photos on this website clearly show Herkimer diamonds covered with a light brown mud (shown in the above photo from Middleville, NY - AD). It is likely that this pocket mud is a combination of original clay, that deposited with the quartz, and material re-worked by ground water. Finding examples of original clay is difficult because so much of the district has been affected by ground water. In addition, it is fairly ugly and not likely to have been saved by collectors - like the photo below of dried mud over quartz druze. Photo Dr. D. - 2008.
In the picture below (Fonda, NY - DA, 2008) the clay is coating second phase dolomite. The clay is often white or cream - different from the re-worked pocked mud which has a brownish color. In both of these pictures it is not easy to see the clay as something significant and probably moving into the rock at the end of when the carbon material came (you can see the black carbon in the above photo). This clay is important in terms of developing a theory about Herkimer diamonds.
Perhaps, as collectors become more aware, they will pay closer attention to the occurence of clay and the black (brown) carbon material. Collect samples, take photos, and help to expand our knowledge about these wonderful mineral deposits.
Web page author - W. David Hoisington, Ph.D.
Below are a two photos (Fonda, DA - 2008) that show the original clay, and how it look different from mud. The first, on the bottom left, is accompanied by black carbon material in a string of small vugs in solid rock that were protected from ground water.
To the left is another common occurrence of the black carbon material - as a film over first phase dolomite. This is very common in Middleville and often associated with small clear Herkimer diamonds (usually 1 to 3). See the matrix page link below. Photo Dr. D., Middleville, NY (AD) - 2008.
Below are two photos of another type of black carbon material from Middleville, NY (AD). Instead of being a coating over crystals this is a substance mixed in with the sandy layer of the rock, but not strickly following bedding, and has a slighly different color. Photos Dr. D., 2008.
To the left: sand grains coated with hydrocarbon showing that it is not following a flat bedding plane. It looks like it flowed into the rock, sort of like colored fluid flowing into a paper towel.
Below is a close-up that shows some of the hydrocarbon as a film in a small vug (top left) and then the lighter gray material on the bottom of the photo (which is the majority of dark material shown in the photo on the left). The difference between the two forms of hydrocarbon ocurrence seems clear.
The photo on the left was donated by Mike Eggleston (2008) and is of a skeletal crystal from Treasure Mt. The inner skelton structure doesn't show well in this photo but can be seen in the lower left and bottom center. But the photo is placed here, as opposed to being on the skeletal page, because it is an excellent picture of the white clay coating (arrow points) the crystal faces of the "skeleton" which is inside the crystal. As is noted on the skeltal page, clay is commonly found in the pockets containing these crystals.
Sand soaked with carbon material
<- Vug with black carbon material film
Mud is a fairly common feature in Herkimer diamond pockets. Most of it is a mixture of clay that came along with the fluids that formed the Herkimer diamonds with clay from ground water movement. The mixed material can be called "mud" whereas pure white (or cream) colored material, rare as it might be, can be called clay. Below is a nice photo of mud on the pocket floor, still a bit wet, donated by Bill and Anne, 2008 (Middleville - AD).
"Anthraxolite" versus Hydrocarbon
It is easy to use the term "hydrocarbon" and it is more accurate that the term anthraxolite.
Tip of a Herkimer diamond ->
On the quartz form page there are some unusual dome like features and concave inpressions in the crystals. It is likely that these curved features are due to the curved surfaces of the hydrocarbon. Below is a picture of bitumen (from an Arab location) that shows its natural curved features.
Any experienced collector in the Herkimer district will easily notice the similarity between the above photos and the hydrocarbon found in association with clear Herkimer diamonds. This association of curved textures on the quartz and curved hydrocarbon material is just another piece of evidence linking the two in the history of Herkimer diamonds.
Please go to the science page for a detailed discussion on this topic of why the name to use for the black carbon material should be hydrocarbon instead of anthraxolite.
Space reserved for more hydrocarbon material photos. Scroll down to the clay photos.
In some cases these curved features are so dramatic that they result in quartz spheres (see the link)
And spheres of black hydrocarbon material.
Spheres from the TCR deposit (access provided by the owner). Photograph is 2 cm across. Photo Dr. D. 2009.
What is in the Bottom of a Pocket?
Sometimes people write to me and ask me what kinds of "junk specimens" would be helpful. The one thing I always say is uncleaned, fresh pocket wall rock - one specimen from the bottom and one from the top (because it is believed that the pockets show zoning).
Below are some photographs of the bottom wall rock from one "mud pocket" at AD (sample donated by Bill and Anne, 2008). Note the mud coating and the rock fragments (at the little white arrow).
If you rinse this mud through a fine screen, and collect what remains, the result is shown below. Note the small size (5 mm scale is given). It is also interesting to note that the rock fragments are angular (not round like from a stream) and the Herkimer diamonds show no damage.
After carefully cleaning the bottom wall rock, it is interesting to see what it looks like. The photograph to the left shows a "mounded" terrain with "valleys" between (something I think is common in many deposits). The mounds are mostly barren while there are crystals tucked into the valleys.
The crystals tucked in the valleys are better seen in the close up view below (see the arrows).
These are "ugly" specimens and nothing the average collector would save. They are just scientific evidence for the History of Herkimer diamonds. To understand the collection of photos of cleaned wall rock, it is important to understand the behavior of the "baby floater" phase, as we know it thus far.
When there is no well developed early druze phase there is no "quartz rind". You can see this in the photographs on the baby floater web page. What this means is that only a small amount of weathering is needed to dislodge the coating of the baby floater phase from the wall rock. This separation will happen at the high points (mounds) while the valleys will still contain vestiges of the little crystals. The material will easily break apart and be found in the bottom of the pocket. Go to the Baby floater page to see photos.
<----Typical black hydrocarbon in a vug
Different black carbon inside sandy rock
The sphere below is about the same size as the large one above ( a little less than one cm across), and of similar form, but it is obviously not black.
The sphere above has an amber color and no crystal form. It has a faint petroleum smell. But most interesting is that it has a "rubber like" form. You can gently squeeze it and it will bounce back to its original form. This is most likely a hydrocarbon. Thanks to Frank for finding this at HBQ (permission to photograph, 2010, Dr. D.). Also see the inclusion page for pics of amber hydrocarbon inside crystals.
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.
