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Calcite - Three Episodes - in the Mines and Deposits within the Herkimer Mining District
Calcite is the last major crystal forming event in the Herkimer Mining District, and occurs in three stages.  The early stages resemble the calcite found within fracture seams in Amsterdam, NY. The latter stages show similarities to the calcite found around Illion, NY.  Overlap of these stages (later on top of earlier) can be found wtihin the district.
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Calcite and Weathering
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Calcite is rarely found without some element of weathering effect.  This will be seen is some of the photos in the accompanying slide show here, but more dramatically illustrated on the weathering page (click button above). The slide show here seeks to present the best examples.
Calcite - Stage 1
The most common form that calcite takes in the district is as flattened “nails head” crystals.  These are called this because from the side view they can look like the head of a nail. The calcite can occur as single disk like crystals up to 120 cm but more commonly average in the range of 3 to 5 cm. It is also quite common for these  disc like crystals to stack next to each other in parallel growth. This calcite is most commonly amber, or honey, but it can be grey. The “nails head” form can also occur with the side prismatic faces elongated - and this shows some variation across the district.
Calcite - Stages 2 and 3
Stage 1 calcite can be found coated with either a layer of white calcite without form, or coated by white to clear calcite rhombs (like skewed cubes).  These white/clear rhombs are commonly small, ranging from 1 to 5 mm across. Occasionally the crystals will be honey or deep amber and rarely the crystals can occur in a scalenohedral form. The final calcite stage is boytroidal, masses of rounded mounds.  In places the form can appear as stacked mounds. The color ranges from white/grey to honey yellow. Both crystal forms of stages 2 and 3 can be found in Illion, NY. as well.
The information, and photography, on this website is copyright protected by W. David Hoisington, Ph. D. unless another author/photographer is cited.
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Due to several injuries Dr C has been forced to put this Herkimer diamond research on hold. Will return this winter (see discoveries page)