Crystals (Field Diamonds) in Tennessee
|This talk was given to the Knoxville Gem and
Mineral Society in March, 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, or in the on-line Powerpoint files
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 range from 12 to 18 meg.
Be sure to view them in Edit Mode, or you may not see the text and captions.
"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.ppt Introduction and geology of Knox breccia-hosted crystals
Quartz_crystals_2.ppt Douglas Dam and Fincher area crystals
Quartz_crystals_3.ppt Morristown exit and Mosheim Anticline crystals
Quartz_crystals_4.ppt Sevier Shale hosted crystals
Quartz_crystals_5.ppt Walland area extension cracks and microphotographs
Quartz_crystals_6.ppt Morphological evolution, quartz varieties
crystals near Saltville, Virginia Site visited at a later
date, distinct from TN sites (This is a