Friday, February 5, 2010

Unakite!

I thought about following a recent trend of daily rock, outcrop, and mineral posts by making one such post per week, then reality hit me over the head and I backed off. This week, however, I have a nicely polished specimen of unakite to show off, even though the specimen isn't mine: I photographed it in Alaska.

Although currently residing in Alaska, this chunk of unakite is from the Blue Ridge Mountains of Virginia. (It's been around.) Unakite, a gemstone sometimes used as a building stone, is a metamorphosed or altered former granitic rock, with a type locality in the Unaka Range of the Great Smoky Mountains of eastern Tennessee and western North Carolina. Callan Bentley describes the origin of typical Blue Ridge Mountains unakite as being a 1.1 billion year old granitoid that got metamorphosed "during Alleghanian mountain-building, between 300-250 million years ago."
This enlargement shows an epidote veinlet cutting some of the reddish pink potassium feldspar in the upper right corner. That's an antique 10X Triplet hand lens for scale.
Here you can see a tiny quartz veinlet cutting the pistachio-green epidote, the reddish-pink K-spar, and the irregular gray masses of quartz.

I first visited the locality where this unakite was collected way back in my undergrad days while on a field trip led by W.D. Lowry. Later, probably while on an outing to some great camping location in the Blue Ridge Mountains, I visited this site with my entire family. My dad collected this particular piece of unakite—somewhere east of Charlottesville, on an east-west road south of the main east-west road heading west from Charlottesville (now I-64), on the west side of the mountains.

I thought maybe I could find the location in Google Street View, but that search was pointless until I did a little research on unakite localities near Charlottesville. And guess what? I think I found our site: somewhere on Highway 56 about one to two miles east of Vesuvius, VA, near an old unakite quarry, possibly between this roadcut and this roadcut. There's a chance that we were on some back road south of Highway 56, but still somewhere within the general Irish Creek–Big Mary's Creek–Little Mary's Creek unakite collection area of Rockbridge County, VA.

I have my own unakite around somewhere, either on a shelf or in a box at the lake. It's one of my favorite rocks, probably because of it's spectacular color, and also because it's likely one of the first rocks I collected as a budding, first- or second-year geologist. (Or maybe a Virginia trilobite was one of my first collections?)

Ron Schott's unakite pebble.

Andrew Alden's polished unakite.

8 comments:

Gaelyn said...

Although unikite's colors are not in my normal fashion palet, it so wonderfully shows the various minerals in large grain, and makes beautiful beads. Interesting post. Going for another series?

Cannibal Panda said...

The K-Spar and Epidote make a stunning combination! If I ever head back over to Virginia I'll have to keep that location in mind and grab a piece.

Cool handlens!!

Silver Fox said...

This isn't really the start of another series, just an average rock post. :)

Silver Fox said...

CP, the hand lens is still in use!

Susan Higgins said...

I never heard of Unakite... thanks for giving me a place to start to learn more about this beautiful mineral.

My favorite thing to do is Rockhounding. Finding locals is always a challenge but definitely part of the fun.

One day, I'll have to take a road trip to find some of these awesome stones! Thanks for the post.

Silver Fox said...

Susan, unakite is actually a combination of minerals, making it a rock (a picky geological distinction!)- I hope you'll have a chance to make it to a collecting site (there are several in Virginia and a bit to the south). If not, you might be able to find some nice samples or polished pieces in a rock shop. Good luck!

Alaska Al said...

That hand lens is not an antique. I bought it for my 1st geology class in 1948. It is still in use and I carry it most of the time.

Silver Fox said...

Alaska Al, I was thinking of antiques as being things older than 50 years, but apparently many hold to the older-than-100-years definition. Purists use that definition.

By Wikipedia's definition #3, I could be an antique, although that definition singles out "older" or "elderly" males over the age of fifty. I'll settle on being called an oldtimer (they use "old-timer" with a dash, and I prefer "oldtimer" without a dash), but think the definition should be expanded to include oldtimer-type women.

MOH says that the hand lens in question is a classic, not an antique (although it isn't a classic car, so maybe it's a classic hand lens).