Questions and phone orders: 10 AM - 10 PM Pacific (760) 920-6465
1 left

gneiss - Proterozoic granite gneiss from the San Gabriel Mountains - display specimen

$ 17.50

This Proterozoic granite gneiss, an orthogneiss, was derived from granitic rocks that were deeply buried and metamorphosed. Pressure and heat caused the minerals to recrystallize and align in bands. Gneiss contains less mica than schist and does not split along mica layers. It shouldn't be a hard sell to convince students that this rock is metamorphic.

An orthogneiss is deprived from igneous rocks. When derived from sedimentary rocks, the gneiss is a paragneiss. A gneiss is often named for a mineral constituent of that gneiss, a biotite gneiss, for example.

George Barrow, 1853-1932, mapped rocks in the Scottish Highlands for the British Geological Survey during the late 19th century, and showed there was a metamorphic progression starting with shale as a parent rock. The series begins with slate, then phyllite, schist and finally, gneiss. Students should be able to recognize examples.

The Barrovian metamorphic progression is often encountered where temperature and pressure increase gradually in areas of active mountain building, subduction and volcanic arcs.

Cut flat on both sides, not polished.





Select a specimen: If more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a black and silver pen, a black mechanical pencil, or one of those plus some number of coins, or you can let us make the selection.

Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.

Shipping: By Priority Mail or Parcel Select Ground, whichever is cheaper. Click > here < for shipping rates. See comment at Note! Use back button to return to this page.