[Rockhounds] photo of an igneous intrusion

[Alan Silverstein]

FYI --

  http://silgro.com/photos/090605_BobcatRidgeHike/I_PegmatiteVein.htm

"Now here was an interesting rock -- and I saw similar veins in other
places.  What happened is that hot magma forced its way into metamorphic
rock, I would call it a slaty gneiss (but what do I know?)  The pink
intrusion, probably orthoclase feldspar, must have cooled relatively
quickly because it's fine-grained.  Note how it "baked" or otherwise
altered the surrounding stone, darkening it."

This is in the foothills west of Fort Collins, Colorado.

Cheers,
Alan Silverstein