American Geode

There’s gold (and quartz) in them thar hills!!!

From our recent new homebase in North Georgia, let’s talk about the Blue Ridge and the Piedmont lands and the geology and minerals of North Georgia. We’ll look at them together, seeing as how the rocks there, the ones that got squeezed and heated up (that’s metamorphic, you know) and the ones that bubbled up from the earth like old volcanoes (igneous), well, they’re cut from pretty much the same cloth.

Now, the old-timers figure that way back yonder, the whole shebang of North America bumped right into this big ol’ landmass called Gondwana, and that’s how they got Pangea, this super-duper continent. That mighty clashing of the earth’s plates, it caused all sorts of cracks and wrinkles in the Blue Ridge and Piedmont here in Georgia. And all that pressure and heat? Why, it just folded and lifted those rocks right up.

The Blue Ridge Mountains, bless their hearts, they’re some of the ancientest hills you ever did see, a whole lot older than those young whippersnappers out west, the Rockies, and even them big fellas over in Asia, the Himalayas. When the Blue Ridge first poked their heads up, they’d have been some of the tallest things around, I reckon. But then the rains came, and the floods, and they just washed away tons and tons of rock and dirt down into the lowlands, the plateau, and even further out. Some folks who study rocks have even found bits of that old wash way out in Arizona, in the Grand Canyon!

Later on, that Pangea thing, which included these very Appalachian Mountains, well, it got all torn apart by more of that earth movin’ and shakin’. Scientists have found pieces of these same Appalachians way down in South America, over in northwest Africa, and even in Greenland, Great Britain, and Europe. But nowadays, all that’s left standin’ here are the tough old cores of these Appalachian rocks.

Now, up in northeast Georgia, them Blue Ridge Mountains make up the highest ground in the whole state. Here in Georgia, these rounded ridges and worn-down peaks go from about sixteen hundred feet up to nearly forty-seven hundred feet above sea level. The whole Appalachian chain goes even further, roughly from Alabama all the way up to New York.

The Blue Ridge, they’re known for that pretty blue haze that hangs over ’em, and for their mighty steep gorges, canyons, and waterfalls. Take Tallulah Gorge, for instance, down there in northeast Georgia. It’s a good six hundred feet deep, making it the fourth deepest canyon east of them Rocky Mountains. Mighty impressive!

Now, the southern edge of the Blue Ridge is near this thing called the Brevard Fault Line. Right on the other side of that line, you got the Piedmont, and it’s made up of some mighty old rocks too. The story goes that these rocks started out as just plain old muddy clay that settled way down deep in the ocean. Seems like mud gets carried the furthest from land that’s wearin’ away, mixes in with some sand, and then just sinks to the bottom of the deep blue sea. Then, when that mud gets squeezed and heated up (that metamorphism again), it turns into mica. And as most folks around here know, Georgia’s got plenty of that sparkly mica.

The rockhounds have also found a lot of this stuff called Metagraywacke, which is just sandstone that’s been changed by heat and pressure. Graywacke, that’s what they call the stuff before it changes, forms in layers of clay and sand that got sorted out in deep water with strong currents. The bigger bits of gravel and sand sink to the bottom first, and then the finer stuff settles on top. Over time, all that gets cooked and squeezed, and out pops Metagraywacke.

Now, there’s all sorts of different metamorphic rocks and minerals in the Blue Ridge area. That’s ’cause it’s been through a whole bunch of episodes with different amounts of heat and pressure and foldin’. Along the western edge of the Blue Ridge, where things weren’t quite as intense, you find slate and phyllite (some folks call it fillite). Then, as you go further in, you find minerals like chlorite (that forms at around two hundred degrees Fahrenheit), shiny silver muscovite, black biotite, garnets, and staurolite. And over on the eastern side, where things got real hot and squeezed tight, you can find kyanite (that takes about eleven hundred degrees Fahrenheit to form!), sillimanite, andalusite, some pretty zebra-striped gneiss, and even migmatites.

And that ain’t all! We got copper, marble (that used to be limestone, like around Tate), talc, this old blue quartz meta-granite (got its color from titanium), quartzite rings around Tallulah Dome, and even some of that igneous granite in the Blue Ridge. Why, even Mount Yonah over in White County is made of this granitic gneiss. It formed way back when molten granite pushed its way up into layers of metamorphic rock.

Now, one more thing you’ll find in both the metamorphic and igneous rocks of the Blue Ridge and the Piedmont is quartz. It can form when hot, watery stuff full of silica pushes into cracks in the rock and makes veins. And gold? Well, gold can be found in those same kind of veins, along with quartz and some other minerals like pyrite. In fact, if you see quartz veins that are stained with iron, that can be a sign that there might be gold nearby. Them gold deposits in the Blue Ridge led to the first big gold rush in America, right around Dahlonega, Georgia. Read our review of the Dahlonega Gold Museum here: http://www.americangeode.com/blog/dahlonega-gold-rush-museum-review/. You can also find a little bit of gold scattered in those igneous granites, but most of the gold folks have dug up over the years came from what they call placer deposits – that’s just old river and stream gravel that’s been worn away over time.

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