Conk OpalIn what is today the state of Nevada in the Miocene, the area was just beginning to collaps
Conk OpalIn what is today the state of Nevada in the Miocene, the area was just beginning to collapse after the building of the highest part of the Rocky Mountain plateau. The area was starting to pull apart, creating lake basins where trees could grow and sediments would flow in. Occasionally, some fallen trees were buried, either just by sediments at the bottom of the lake or by a nearby volcanic eruption that sends some ash into the basin.Those sediments were buried, and a few million years later Nevada was faulting and pulling apart, creating new fractures where groundwater could flow. Water flowed through those sediments, dissolving some of the silica and moving it around until it hit those buried trees. The dissolved silica replaced some of the material of the tree, turning it into petrified wood, and began filling the fractures with even more silica. That silica in the open fractures became the brilliant iridescent opal seen in this sample.This sample is being auctioned later this month by Bonhams and is 6 centimeters in the long direction.-JBBImage source: https://www.bonhams.com/auctions/26082/lot/133/?category=list&length=214&page=1 -- source link
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