Getting the Rock Ready: A series of geologic events all overlapped in one place to make a special “birth place” in limestone. We needed a rock that had lot of holes in it with enough room for the Herkimer diamonds to grow. A very unique series of events took place that helped make this porous rock (one with holes - see example photo).
Step 1a: The Stromatolite Invasion!
Scientists believe that around 600 million years ago the whole Earth was covered in ice - an event call “Snowball Earth”. There was a mass extinction of life with this event - but bacteria survived (cyanobacteria). These life forms developed into the colonies that make what are called stromatolites.
Step 1b: The Massive Uplift - Caves
Even before this “birth rock” was changed from mud into solid rock the area was beginning to experience earthquakes (the rock, in isolated places in the Herkimer District, shows signs of this earth movement). There were multiple shifts in the sea level resulting in multiple “stomatolite layers”. This layering s something we observe in the Herkimer Mining District and it has an effect on the mineralization which occurred a bit later. Then the rock was buried and solidified. Then it was uplifted and exposed to the air. This resulted in a “cavity forming” (called paleokarst) world and the making of more holes in the future birth place for Herkimer diamonds.
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From 550 million years ago up to the age of the Herkimer diamond host rocks, about 500 million years old, stomatolites were vast in numbers. It is likely they changed form during the time of the Herkimer host rock, lending the rock a more porous nature.These stromatolites DID NOT make Herkimer diamonds. If they had then they would be common in similar rocks around the world.
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Dr C will presentHerkimer Diamond Discoveriesat the 2017 Herkimer Diamond Festival