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Centre for Earth and Environmental Science Research

Characterisation and Growth Mechanisms of "Herkimer Diamonds"

Executive Summary
ResearchersJohn Quaife, CEESR
Prof. A. Rankin, CEESR
Prof. J. Clemens, CEESR
Funding Body/SourceKingston University
Duration2007 -
Project Summary

"Herkimer Diamond" is the name given to the doubly terminated quartz crystals of exceptional clarity, much valued as semi-precious gemstones. The type locality is Herkimer County, New York where they occur in the centre of crystal- lined vugs and cavities, often together with tarry bitumen (FigB), in dolostones of Cambrian age.

Doubly terminated quartz crystals with similar clarity and an association with hydrocarbon-bearing inclusions have been reported from a number of large other worldwide localities Local names such as Patagonian Diamonds (Argentina), Hindu Kush or Himalayan Diamonds (Pakistan) Marmarosh Diamonds (Ukkraine) and Merthy Diamonds (Wales) are applied to such specimens to distinguish them from those found in Herkimer County and surrounding areas of the Appalachians

The current research aims to investigate the reasons for the characteristic bi-pyramidal shape and optical quality of "Herkimer diamonds" and their tendency to trap large hydrocarbon-bearing liquid, solid and vapour inclusion.

The working hypothesis currently being tested is that these crystals grew under slow, stable hydrothermal growth conditions in the presence of hydrocarbons which acted as growth inhibitors.

Slow growth rates would also favour the production of larger inclusions as growth (depression) imperfections would take longer to seal over than during periods of more rapid growth. This suggestion, together with the idea that the bi-pyramidal shapes are due to free (ie suspended) growth in a cavities filled with viscous hydrocarbons or clays, will also be evaluated.

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