History of the Herkimer Diamond  Host Rock

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Broad continental changes creating the setting for the making the Hermimer host rock

Changes in the world that happened just before the birth of the Herkimer host rock

This presentation shows a representation of multiple conditions during the time when the Herkimer host rocks were being made and the time just immediately following. An important feature is the presence of stromatolite layers - but they are only a part of the story.  Stromatolite layers, of this same age, occur all over the world.  Only in the Herkimer district do these layers contain the many different Herkimer diamond deposits.  What is important to consider are all the various geologic events that combined to shape the Hermiker host rocks. Along with unique "open" (framework)stromatolites, there were sand layers and erosion events. Later there was the formation of collapse breccias and other karst features (known througout the  world during this period in geologic history).  It is the combination of a unique set of events that gives us a very porous layers in a carbonate sequence, now called the Herkimer host rock.  It is a rock primed and ready for the growth of Herkimer diamonds.

There is some question about the nature of the porous layers.  There is little doubt that layers with high porousity existed, but exactly when did they develop the larger "pockets".  This is a question that will be explored in the next presentations - one on faulting and the one on glaciers.

This presentation (which is not available yet - more research needed) describes conditions after the host rocks were first formed that probably affected the formation of Herkimer diamond deposits.  There are basically two sets of events  that happened after the host rocks were burried to about 4000 feet.  First was faulting,  big cracks in the Earth along which large blocks of rock were shifted up (or down).  Second, there was fluid movement along these faults, and then out into porous (connected holes) layers in the rock.   It appears that  certain fault orientations were more conducive to fluid movement and certain layers in the rock more open to fluids moving through them. There is little doubt, based on field evidence and drill core samples, that these two events occurred within the Herkimer host rock (in specific areas).  A review of the "General Mineral Sequence" for the district suggests that there were many different fluid movement events linked to the formation of minerals in the Herkimer district.  What is still in hot debate is the timing of these faulting events and their exact relationship to the formation of Herkimer diamonds.  Thus far, a precise date for when the Herkimer diamonds were formed is not available.  Most researchers agree that it happened some time after the first faulting, and before the last of the faulting for the region. Thus there is often a link of the age of Herkimer diamonds to major continental collision events. 

The effects of glaciers and man on the appearence of Herkimer Diamond deposits was critical to having the Herkimer deposits become available to the public.  The glaciers removed hundreds of feet of rock exposing the Herkimer host rock to the surface and then man located the deposits and made them known to the public.  It is also imortant to note that the last geologic event to affect the Herkimer diamond deposits was erosion - water running through the rock and weathering both rock and crystals.   In some places there are large empty holes, or what might be called "mini-caves", in the Herkimer host rock.   In interviewing experienced collectors, many have recounted stories  of these empty holes. One mine owner said that there was one big enough to sit in,  Another collector spoke of one six feet long, and a couple of feet high, with only a single crystal tucked way in the back.  The recent weathering has also had an impact on the minerals - fractures in larger Herkimer diamonds, etching of dolomite and calcite, turning sulfides to rust, and moving around mud and small rock fragments. 

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"Major events were the Taconian orogeny, caused by a collision with a volcanic island arc 460-440 m.y. (million years) ago; the Acadian orogeny, caused by a collision with a microcontinent called Avalon 410-380 m.y. ago; and the Alleghanian orogeny, caused by a collision with West Africa 330-250 m.y. ago."

It is obvious that several mineral fluid events moved through the Herkimer host rock.  Please click on the minerals tab at the top of the page to see the sequence.  What we do not know is exactly when these events happened.  Currently it is a process of gathering "clues" and piecing together the best fit explanation.

We also do not know the exact timing of the mineral events in relation to the various "mountain building" events.  More research is also needed here.

Please note that there are also YouTube versions, but they are of lower quality