HerkimerHistory.com
This site was last updated on August, 2010
Definitions and Scope:

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 right is a picture of the typical hydrocarbon on second phase dolomite (TCR, 2010).  You can see the curved shapes it commonly makes and how it can fill in a cavity.   These are the common forms, 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.

Please help with picture donations!

Other Minerals - 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. much like the sphere on the right, which is most likely a hydrocarbon.  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).

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.
To the left is another common occurrence of the black carbon material - as a film over first phase dolomite in the "Vug Zone".  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.

<- Vug with hydrocarbon film

"Anthraxolite" versus Hydrocarbon

It is easy to use the term "hydrocarbon" and it is more accurate that the term anthraxolite.
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 middle East bitumen sample 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.

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.
<----Typical black hydrocarbon in a vug
Different black hydrocarbon 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.).  
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.

Clay and pocket mud has its own web page - click here.

To the left, also of interest, are the flat sheets of marcasite. 
To the right is another common occurrence of the hydrocarbon material - as shiny curved forms over first phase dolomite in the "Vug Zone".   Photo Dr. D., Fonda, NY (AD) - 2008, 1 cm across. The dimpled texture is not common.
Sand soaked with carbon material
Bitumen sample from Middle East
aaaaaaaaaaaaiii