It was a beautiful fall day as Field Trip Team Leader, Bob Hohn, signed members in at the CCGMS field trip on November 10, 2012 . Bob manned a table and had samples of smoky quartz, skeletal quartz, and quartz crystals that members could find at the mine. There were 15 members from CCGMS and GMS in attendance. A second group of Rockhounds from the Aiken Mineral club arrived at the mine and new friends were made.
The dig went well with Bob and Chris Munson helping members find slabs of skeletal quartz, and quartz crystals. One member found a beautiful smoky quartz crystal. Members left the mine with buckets full of quartz crystals, slabs and nice quartz specimens.
This mineral vein was formed by a process that makes “hydrothermal rocks”. Hydrothermal rocks form from a very hot watery fluid that either flows through fractures in pre-existing rocks or that permeates throughout the tiny void spaces that exists in all rocks and sediment. These hot water solutions carry many dissolved elements which can deposit a wide range of minerals in the fractures. The origin of these fluids is always a bit of a mystery, but they are commonly associated with mountain building events where igneous magmas intruded and crystallized to form local granite pods. The Diamond Hill “hydrothermal vein” is inside of ancient igneous rocks that intruded about 400 million years ago during the Ordovician geologic time. Our first eastern mountains formed at that time as the North American plate collided with a large island in the pre-Atlantic ocean. With two more mountain building events to come, exactly when these fractures were filled with the hot watery solutions that deposited the Diamond Hill quartz is uncertain; but we know that there were multiple times when the hydrothermal fluids advanced and retreated through the veins.
The skeletal quartz has recorded these advances and retreats; beginning with growth of an inner crystal, then dissolving of the early growth along select planes leaving high ridges (like skeletal rib bones showing through the fur of an underfed dog), finally followed by a smooth outer layer of clear quartz which is deposited over the entire crystal by the last advance of the watery solutions. All of this happened long ago deep in the Earth and for the last 200 million years, erosions have slowly worn away the overlying rocks and deposited layer upon layer of mud in the vein to cover all the quartz, now to be uncovered by eager Rockhounds visiting the mine.
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