by John Anderson
On a bright and crisp day on January 28, 2023, 14 folks from CCGMS met for a joint field trip with the Knoxville Gem and Mineral Society at Douglas Lake in Tennessee. With the lake being drawn down during the winter months by about 20 to 30 feet, so to be able to allow space for the Spring Rains, a wide area of what usually is the bottom of the lake was exposed for us to wander around to find what the locals call Douglas Lake Diamonds.
These are transparent doubly terminated quartz crystals that formed in vugs in the rocks that make up of the southern portion of Douglas Lake. (For more information about the quartz crystals of this area this link has a PDF file about the Douglas Lake Diamonds: https://gsa.confex.com/gsa/2016SE/webprogram/Handout/Paper273719/TN_quartz_crystals_2016.pdf)
To find the quartz crystals you had to look for the flash of the sunlight off the crystal faces of the quartz crystals.
During the construction of the dam for Douglas Lake they encountered solution channels within the Knox Dolomite that were filled with volcanic ash from the volcanoes that were erupting during the Middle Ordovician as the ancestral Appalachian Mountains were forming during the Ordovician (Taconic orogenic event). Within the Ash deposits they found vascular plant fossils of some of the first land plants known, as well as arthropod fossils (crustaceans [crabs] and merostomes [relatives of horseshoe crabs] (https://www.journals.uchicago.edu/doi/pdfplus/10.1086/625214 )
Along with the quartz crystals hematite and limonite (goethite) was found within the sediment. These minerals have been rounded by the moving water of the lake so they are rounded sand and pebble size particles.
There were also some fossils that had weathered out of the Dolomite as well as modern clam shells were also found on what had been the bottom of the lake.
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