Weathering (and Iron Oxides, like rust) in the Mines and Deposits within the Herkimer Mining District
Weathering, the effect of water and ice, on the mines and deposits of the Herkimer Mining District is always present - somewhere in the mine. This is
particularly true in the deposits that are very close to the surface, like Hickory Hill.
At times collectors can encounter small cavities (up to 2 ft) that have totally smooth walls - no crystals of any kind, not even the very early dolomite. In many
areas the second dolomite, and the first calcite, show heavy etching from weathering. Often the sulfides have been changed to rust coatings, or lumps of iron
oxide (likely a mixture of limonite and goethite). In the slide show there will be side - by - side photos, non-weathered and weathered.
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Weathering and Herkimer Diamonds
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Weathering has had a dramatic effect on
Herkimer diamonds. It is quite difficult to
find a crystal larger than 3 cm long that is
without flaws (although a few 4 cm ones
have been reported to this author).
Smaller clear crystals, less than a cm,
are very common. The dominant
process causing these fractured in the
crystals is the weathering - the forces of
water freezing and causing the crystal to
crack. Larger crystals have more surface
area and thus receive more force from
the water freezing. Larger crystals also
tend to have internal structural weak
points created during the growing
process out of a hypersaturated solution
(see the hopper - skeletal page).
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by W. David Hoisington, Ph. D. unless another author/photographer is cited.
There is some other evidence to support
this linking of flawed crystals to ice
pressures. Herkimer diamonds are found
totally encased within calcite. This calcite
has served as a protective shield against
the ice pressures. The Herkimer
diamonds within calcite are almost always
without fracture flaws. This is shown in
the slide show, along with a series of “size
versus flaws” photos.
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Thank you Shannon Haley
Wilbur for the donation of 30
samples from the Fonda
region.1/05/2019 and 3/2/2019
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