Sevier Shale

Quartz crystals in the Sevier Shale show that at least some
quartz deposition took place during or after the
Alleghenian Orogeny.

The other geologic environment where quartz crystals occur is the Sevier Shale.  Here, they are also found in open space within vugs, although again, there may have been some soluble component, now gone, present when they formed. Rock salt could have constituted such a matrix, and again, anhydrite is common in rocks at depth, for example in East Tennessee’s zinc mines.  But again, if it was there, it would still be present in the inclusions.

Seveir Shale crystals tend to be simpler.  There is little or no evidence for more than one stage of growth, but you will find some multiple parallel crystals.  The Sevier Shale was deposited after the post-Knox unconformity, and all open space is the result of later deformation (faulting and folding) that took place during the Alleghanian orogenic episode.

Dolomite and calcite-lined vug from the Sevier Shale.

Excavation along
Andrew Johnson Highway
(locality 13)

Crystals in vugs in sheared and deformed shale bedrock

This fairly recent excavation into the Sevier Shale was found while scouting near Mosheim for exposures.  A few crystals were noticed on the ground and traced to vugs in the deformed bedrock.



Stitched-together photos of theroadside excavation.

The exposure was then examined close-up with printouts of the photos in hand, and the features plotted on the photos.

Same, with photo background removed.  The geology was revealed as complexly deformed, as expected.

Calcite-filled vug with crystal.  Doubly terminated bipyramidal crystals were also found completely loose in some vugs.  This crystal was not “loose” only because it had impinged on the cavity walls.

Very transparent quartz qrowing on calcite matrix.  The reflection is from an “s” face, which allows one to determine the handedness of a crystal.

Typical crystals from this locality. Crystals with "s" faces are occasionally encountered here, but they are no where common.

Well-formed “Herkimer” from this location.

Another well-formed “Herkimer” from this location.

Muddy Creek arm of

Douglas Lake

(locality 6)


Many fresh crystals of local origin plus a few slightly water-worn

Muddy Creek arm of Douglas Lake is a well-known locality where crystals can be found on the surface in crumbled Sevier Shale, and in soils derived from that formation.

Some of the typical crystals from Muddy Creek.  Many have clouds or "veils" of microscopic dark inclusions, which make them look like smoky quartz.  Note that almost all of them are bipyramids.  There are few hexagonal prisms, and none of the “scepter” forms where bipyramidal is deposited over prismatic quartz.

Mud inclusion crystal.  The mud inclusions are deep embayments defined by partially overgrown septa.

The same crystal looking down the “c” axis.  The mud inclusions are deep embayments defined by partially overgrown septa.

Detail of above.  The margins of the septa are growth surfaces, not broken surfaces.

Diamond Creek
(locality 9)

All crystals found at Diamond Creek show evidence of transport.

 Diamond Creek has a variety of forms, and is unusual in the number of distorted-appearing or “squashed” crystal shapes.  The spot is also different in that almost all the crystals occur with gravels that have been transported by the creek.  This is reflected in the presence of at least some chips on the points and edges.

Large complex bipyramidal crystal.

Large smoky crystal, bipyramidal habit.

Deformed shape.  Front face is an “m” prismatic face, with the “c” axis going from lower left to upper right.

These distorted crystals are all oriented with the “c” axis vertical.

NEXT

Crystals near Walland

(Locality 4)

Contorted and sheared Sevier Shale.

Quartz_crystals_5.htm

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