Double terminated crystals are illustrated on the internet from a number of sources including cracks in Septarian nodules from the French Alps (http://www.quartzpage.de/dia_text.html),  and northern Ohio (http://www.vasichkominerals.com/Lamereaux1.html).  The famous “Herkimer diamonds” occur in irregular vugs and cavities within undeformed Cambrian dolomites in upstate New York.  Many images can be found online, for example http://www.quartzpage.de/her_text.html.


Crystal from Pakistan.  The inclusions are brown in transmitted light.


Crystals sold to me as being from Tibet. 



Phases of SiO2, with typical geothermal gradient ranges.  The high Pressure phases coesite and stishovite are not shown.  Note that pressure is shown increasing in the downward direction.

Quartz crystal showing typical morphology, and stereo plot. “S” and “x” faces allow one to determine the handedness of the crystal, but the s faces were only seen in a few specimens from one locality, and x faces have not yet been observed.   More commonly developed faces are shown with larger font.  Also shown are the uncommon ‘p and ‘? faces seen on some crystals from the Walland occurrence, plotted from angle data tabulated in The System of Mineralogy - Volume 3 Silica Minerals by Clifford Frondel (Jan 1, 1962).  These have not been independently determined.


Known locations for “Herkimer” type quartz, along with dolomite breccia-hosted barite and zinc deposits, and major faults with shaded relief overlay.  Basemap and faults from the Geologic Map of Tennessee, 1:250,000.


Brief geologic history of East Tennessee, in four stages.



Stratigraphic units of the Valley and Ridge Province of East Tennessee.  Quartz crystals occur in open space within collapse breccia bodies in dolomites of the Knox Group, and in vugs and cavities within the Sevier Shale that were opened  by deformation associated with the Alleghanian Orogeny.



Time Line, with age range for crystals relative to potential open space. Crystals found in the Knox breccias could have been deposited during the entire time interval from shortly after the formation of the unconformity to the relatively recent geologic past, while those in the Sevier Shale and any younger rocks could not have formed  before the orogeny created open space through tectonic deformation. There were good images available of karstic processes and paleokarstic collapse breccias at Zeng, H., Wang, G., Janson, X., Loucks, R., Xia, Y., Xu, L., and Yuan, B. (2011). ”Characterizing seismic bright spots in deeply buried, Ordovician Paleokarst strata, Central Tabei uplift, Tarim Basin, Western China.” GEOPHYSICS, 76(4), B127–B137

Douglas Dam area at relatively high water.


Douglas dam area at mid water.

Features and the shoreline on the day I was there mapping, when the water was lower still.  Areas without crystals were not included.

Features used to compile map, with inferred contacts.

Interpretative geologic map.

Virtual field trip to the Douglas Dam area.




Outcrop with post-Knox unconformity contact.  Lenoir Limestone forms upper half above white bed.

Unconformable surface, detail.

Fossiliferous Lenoir Limestone just above the unconformity.

Orthocone (Michelinoceras) beds above the Lenoir Limestone.

Sevier Shale along shore farther to the south.

Dolomite veins in crackle-brecciated dolomite.

Universality of crackle-type breccias.  This one is on Mars, photo courtesy of JPL, NASA, and the rover Opportunity.

Outcrop with pyrobitumen vein, where I uncovered it and washed it off.

Closer view of pyrobitumen vein.

Close up, wet.  The whitish fragments are crystalline vein-filling dolomite.  Quartz crystals appear bluish gray.

Dry, showing the quartz crystals better.

Calcite-filled vugs as a growth medium, a potential explanation for some of the things we see in these crystals.  These exposures are in the same beds as those near Douglas Dam, a few miles northeast along strike.

Closer view.

Large chert and calcite nodular feature, possibly of algal stromatolitic origin.



Close-up of massive calcite

Index