Here’s a sweet little sample of migmatite (~470 Ma late Ordovician Taconian Orogeny, U/Pb date from zircon), that my students and I spotted last week on the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province:
Note the white translucent quartz, the orangey (partially kaolinitized and rusty stained) opaque potassium feldspar, and the shreds of biotite torn and tangled between them:
I love the fact that I have such easy access to gorgeous migmatite here in my local stomping grounds. It’s a profoundly satisfying experience to watch the comprehension of “birth of a granite” dawn on my students’ faces when we visit these terrific rocks.