#slickenlines

[earthstory]

Golden Fault This sample is a piece of one of the gold-bearing mountains in California. The gold was likely deposited as a hydrothermal vein – hot waters associated with the growing volcanic mountains flowed through the ground, dissolved components like gold and the vein quartz you can see sticking out the side, and then deposited those dissolved elements where there were cracks.

If you look carefully at this sample, there is a fabric of small grooved lines running down from the top right hand corner of this sample. These are described as slickensides – grooves that are created as rocks are moving and grinding past each other in a fault zone. Fault zones are good places for fluid flow and mineralization since they’re open cracks that run substantial distances through rocks. Whether this gold was deposited during fault motion and the slickenlines represent a pattern in the rock controlling the gold growth, or the fault kept moving after the gold grew and the gold was ground into…this is truly a golden fault. This sample weighs just about half a kilogram and is about 10 centimeters wide. It is available for auction later this month from Bonhams. -JBB Image credit: https://www.bonhams.com/auctions/26082/lot/164/?category=list&length=214&page=1

[earthstory]

Let's head out along with a field trip! Dr. Craig Grimes from Ohio University takes a group out to a fault and examines slickenlines (slickensides), a feature formed in faults when the rocks move and grind past each other.