Day #9 Outcrop: Anorthosite Highway Roadcut

IMG_8484From Tupper Lake to Saranac Lake in the Adirondacks of New York State runs NY 3, better known to geologists of the region as the “Anorthosite Highway”. There are some lovely pristine roadcuts through the Late Proterozoic Marcy Massif anorthosite, though many don’t offer a great deal of shoulder room to park your vehicle. Today’s featured outcrop is one of the more accessible roadcuts, located just east of Bartlett Carry.

Anorthosite Roadcut

In my pre-GigaPan days I was already experimenting with stitched panoramas. But what do you do with a 28 megapixel image? It’s too large to upload to Flickr and too small to upload to For now I host it on my own site.

Aligned Plagioclase Crystals

Although these rocks have experienced borderline amphibolite/granulite facies metamorphism, they largely retain their original igneous textures at this location. The plagioclase crystals that make up this anorthosite were probably concentrated by buoyancy (floating) in a dense ferrodioritic magma.

Up close, you can see the classic opalescence that is characteristic of some labradorite compositions…

Opalescence (or Labradorescence) in Plagioclase

And to take the chill off a cold winter’s night as I post this, here’s a reminder that summer is just a few score of blog posts away…

Black-Eyed Susan
Bookmark the permalink.

Comments are closed.