Tennessee Field Diamonds
A treasure 485 million years in the
Quartz crystals in the
Sevier Shale show that at least some
quartz deposition took place during or after 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 Tennessees zinc mines. But
again, if it was there, it would still be present in the
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.
Andrew Johnson Highway
Crystals in vugs in sheared and deformed
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
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
Muddy Creek arm of
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
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.
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.
and sheared Sevier Shale.