The December 2007 edition of TAW was hosted by goodSchist.com — check out the original here.
This month’s Accretionary wedge is Deskcrops/My Pet Rock. A tour de force of rock collections, concentrating on the world’s geobloggers detailing their favourite samples. Why are they so interesting? What’s their history? Read on to find out.
A cherty mudstone was fractured and invaded several different times by mineral-depositing solutions, then nicely rounded in the Pacific surf.
and a Serpentinite Boulder
Photos can’t capture all the color and textural appeal of this serpentinite specimen, polished by deep movements in the California Coast Ranges.
Next up, Chris Rowan from Highly Allochthonous gives us a desktop full of Komatiite;
I’ve been meaning to discuss this one for a while: even though it’s not the prettiest in my collection, it tells a very interesting story about the early Earth.
If you want to know just how a rock changed shape, it helps to have a way to tell apart pure shear and simple shear. Generally, you need to find some kind of object that has tracked the movement – and this rock has one.
Stopping along Highway 62/180 in between Guadalupe Mtns National Park and Carlsbad Caverns is a favorite for geology field trips of any kind. At this location, you are not in any national park and can smash and grab as much of this rock as you want.
See how many of the deskcrops you can identify on your own – when you recognize one you can “Take a Snapshot” and add a comment.
The subject of fulgurites, or fossil lightning, came up and I explained that quartz has a melting point of about 1600 degrees C, a temperature easily achieved in the near surface, though in very wet soils the charge can be dissipated pretty rapidly.
My first trophy rock is a 4 kg boulder of the Lavras conglomerate from the Tombador formation of the mid-Proterozoic Espinhaço Supergroup.
And to round out the deskcrop theme, here’s all of the deskcrops described by thermochronic from Apparent Dip;
Thanks a lot to everyone who’s participated.