Quartz Crystals (Field Diamonds) in Tennessee
by
Martin Kohl


This talk was given to the Knoxville Gem and Mineral Society in 2013. In addition to my own pictures, it included some spectacular ones of related specimens from the internet. Their use in the talk would come under "fair use", but unfortunately, reposting them here would not. I removed them here, but there are links or search terms to bring up the same or similar images.

The Powerpoint file had to be cut into six pieces due to a 20 megabyte upload limit on the server. They ranged from 12 to 18 meg. They were later re-cast to typical vertically arranged web pages.


Abstract

"Field diamond" type crystals are found in many places throughout the world.  In Tennessee they have been found in two geologic environments and their overlying residual soils: firstly, scattered locations associated with breccias in the Knox dolomite, and secondly, with zones of folding and faulting in the Sevier Shale.  Their distribution may reflect geochemical zoning that also controls the distribution of zinc and barite deposits.  The greatest variety of crystal habits is found in the Knox breccia environment, often showing multiple stages of deposition, as well as breakage and regrowth, while the Sevier Shale crystals tend to be simpler.  There is a consistent morphologic change from earlier more prismatic crystals to later bipyramidal overgrowths seen in the Knox crystals that points to a change of environment, perhaps an increase in temperature.  Many crystals also show evidence of later modification by processes of transport and erosion, and possibly by the action of moving groundwater.  Additionally, these crystals may provide some insight into factors that control open-space quartz deposition; whether silica forms drusy quartz, agate, or field diamond type crystals.


Quartz_crystals_1.htm Introduction and geology of Knox breccia-hosted crystals

Quartz_crystals_2.htm Douglas Dam and Fincher area crystals

Quartz_crystals_3.htm Morristown exit and Mosheim Anticline crystals

Quartz_crystals_4.htm Sevier Shale hosted crystals

Quartz_crystals_5.htm Walland area extension cracks and microphotographs

Quartz_crystals_6.htm Morphological evolution, quartz varieties

Quartz crystals near Saltville, Virginia Site visited at a later date, distinct from TN sites.


Resources

http://www.quartzpage.de/index.html: Exhaustive treatment of all things quartz. Excellent clear discussions of many topics, and photos far superior to those on this site.

Poster presented at the 2016 SE section Geological Society of America using much of this material, but better focused.
Abstract:
https://gsa.confex.com/gsa/2016SE/webprogram/Paper273719.html
Poster (15 Mb):
https://gsa.confex.com/gsa/2016SE/webprogram/Handout/Paper273719/TN_quartz_crystals_2016.pdf

 

 

 


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