13 October 2017

Friday fold: ptygmatic vein from Finland (NMNH)

Posted by Callan Bentley

Happy Friday! Here’s a sample from the Smithsonian Institution’s National Museum of Natural History in DC:

As the label says, we have a nice example of ptygmatic (“intestine like”) buckle folding here. It comes from Finland. The coarse equigranular crystals in the vein appear to be mainly potassium feldspar and quartz. The surrounding matrix has a pronounced foliation. Note the cuspate “flames” of matrix between the broad “lobes” of folded vein. These two materials were behaving quite differently at the time of folding. It’s a lovely sample.

And I hope you have a lovely weekend.