Peridotite: A New Gallery
Tuesday November 3, 2009
After a slow drive last month through the eastern Klamath Mountains, with many stops to take pictures and examine rocks, I now consider myself well acquainted with peridotite. That can be hard to do, because peridotite is almost all deep in the mantle and lower oceanic crust. And most of the peridotite that does make it onto the continents is altered into serpentinite. Of the little that is left, California has the nation's largest share, and most of that is in the eastern Klamaths along the upper Trinity River north of Trinity Lake on state route 3 and Trinity County route 17, the Trinity Heritage National Scenic Byway. Most of the pictures in this new gallery come from there.
Peridotite hand specimen — Geology Guide photo
Comments
Thanks for posting your peridotite gallery. I live near the region where you photographed some of your specimens. I’m often not sure what minerals I’m seeing in rocks of probable peridotite origin that are serpentinized or weathered to various degrees.
By the way, I recently had a hike in a serpentinite area, Horse Mountain, near an old copper mine location. In some areas the surface rocks had very evident malachite crusts. The same rocks contain some crystals of, I think, calcopyrite. I have been told that that mine and another nearby produced some veins of metallic copper. I wonder what type of geochemistry might reduce sulfides to metal?
Is gold more common in these areas?
I don’t think so. Gold concentrates in quartz veins that issue from granitic intrusions–that is, highly refined crustal rocks. Peridotite is straight outta the mantle.