Geologists out there?

[Rockhound]

Was wondering if there are any geologists on the forum? I do environmental/geotechnical geology and geophysics in NC. Govt and private clients, some mundane projects, some really rad ones.

What about you?

 

[colonel00]

Not a geologist but I do have something I have been wanting to ask a geologist about. I will get some photos posted but I came across a river rock this summer up in Alaska. It was a typical egg shape except it has somehow been split in half in a perfectly straight fracture. On both of these exposed sides it appeared that rust has formed although there was no indication of rust on the outside of the stone. So, my assumption is that there was iron in the rock which had rusted and been worn away long ago on the outside but the fracture exposed new iron inside the rock which was now exposed to the elements and oxidizing. Am I on the right track?

 

[WyoBowhunter21]

Nice! The sounds awesome. My degree is a cross discipline between petro engineering, geology, and business. Last year I was a cement engineer which was really cool. I did a lot of work with working on formations. I got out of that and now am doing something completely different. I hope to get back to the geology/engineering side soon

 

[Vids]

I'm a civil engineer, so we're somewhat in the same arena.....

 

[Rockhound]

Not a geologist but I do have something I have been wanting to ask a geologist about. I will get some photos posted but I came across a river rock this summer up in Alaska. It was a typical egg shape except it has somehow been split in half in a perfectly straight fracture. On both of these exposed sides it appeared that rust has formed although there was no indication of rust on the outside of the stone. So, my assumption is that there was iron in the rock which had rusted and been worn away long ago on the outside but the fracture exposed new iron inside the rock which was now exposed to the elements and oxidizing. Am I on the right track?

Post up some photos, that'd be good. Does the whole inside appear "rusty", or are there veins of "rust" running through it? Either way, you're probably just looking at an iron-rich sedimentary rock. Veins of iron rich material may have intruded the sedimentary unit, or the whole composition may be heavy in iron, causing the whole thing to appear that way. Both are common in the lithification of sed rocks.

The egg shape indicates it's been weathered a lot, probably down a river like you said The first thing to change as a rock weathers in this fashion is the outward appearance. Crack open a river rock from here in NC and you will see quartz crystals and color variations that are just beautiful, but the rock was pretty dern ugly on the outside. In geology, there is always more than meets the eye

 

[Rockhound]

I'm a civil engineer, so we're somewhat in the same arena.....

Yeah we are! I work with a ton of civils. Funny when I get together with my sister to talk about how different our studies were in college and how the research I did for my MS was just completely off the map from what she did, and now our day-to-day work overlaps like I would have never guessed. Ha.

 

[Ray]

Physical Geographer - minors in geology and biology - with over 24 years in the environmental investigation and cleanup business on both sides of the table. I never did get around to taking a minerology class for my minor, so my friends don't let me discuss rocks unless I am supervised.

 

[MAT]

I guess I'm the only other real one thus far? State gov't employee overseeing the cleanup of groundwater contaminated sites. And in my world civil engineers can only hope to be as smart as a geologist

Badgers make better geologists! Unfortunately not championship winning football teams though.

BTW the rock described above sounds like a leaverite. My wife knows them well.

 

[ChrisS]

environmental scientist here. Worked on everything from gas station and dry cleaners to multi-site munitions remediation. I pursued this career because I liked being outdoors and didn't realize that in this career field, you're spending your time in the worst parts. I've been on some real nice landfills and have seen some massive whitetails though.

 

[norsepeak]

Not a geologist, but I did stay a holiday inn once, does that count?

 

[avodude]

Former geologist here. Did some mud logging for oil and gas in Wyoming and geothermal in Nevada before working as a drilling project supervisor at the Hanford Nuclear site. Gotta love radiation! After layoffs in both jobs due to fluctuating prices of oil and spending in environmental cleanup, I decided to get a degree in electrical engineering. Two more semesters and I will be done! But I still love geology and will always. It just didn't fit career-wise.

It is true that the ugliest rocks are usually the most interesting to geologists! Post up pics of the rock! Haha

 

[colonel00]

Post up some photos, that'd be good. Does the whole inside appear "rusty", or are there veins of "rust" running through it? Either way, you're probably just looking at an iron-rich sedimentary rock. Veins of iron rich material may have intruded the sedimentary unit, or the whole composition may be heavy in iron, causing the whole thing to appear that way. Both are common in the lithification of sed rocks.

The egg shape indicates it's been weathered a lot, probably down a river like you said The first thing to change as a rock weathers in this fashion is the outward appearance. Crack open a river rock from here in NC and you will see quartz crystals and color variations that are just beautiful, but the rock was pretty dern ugly on the outside. In geology, there is always more than meets the eye

Here are some quick cell phone pics.

 

[avodude]

Like Rockhound said - obvious rounding from being in a stream bed. Color of the rock is dark, we would call it "mafic" meaning that is rich in magnesium and iron. Could be a basalt or gabbro, I'm guessing. Where you were in Alaska could help determine what kind of rock it is. I can see others patches of rust in the top and bottom photograph. How it split in half, like it did, I cannot say. Looks like it has a dark circle in the middle, photos 2 and 3, which may have been an inclusion that caused the rock to fracture along the inclusion's plane.

 

[poisonarrow]

Wow that almost looks like a sweet potato. Hah, no geologist here.

 

[mallacootasmoothie]

I found this 15lb rock in a river bed, it was in the bottom of a bowl that it had worn out.
Until I see rounder, I'm claiming it as the roundest rock in the world.

 

[Warren1726]

That is, indeed, a round rock!

 

[rmh2282]

I'll second that it looks like a sedimentary rock. Only igneous rocks are classified mafic or felsic, and sedimentary rocks are classified by their grain size. This is seemingly a sandstone because the grains (for the most part) look to be no bigger than 2 mm. Any bigger than that and you would have something called conglomerate or breccia, which you can see a gorgeous chunk of sitting under the roundest rock in the world.

I think the clean fracture in the sweet potato is probably due to frost wedging, where a small crack forms from weathering/abuse and seeps water inside that expands when it freezes.

I'm in my junior year of geology right now at Radford University in VA which is pretty close to NC. I just transferred into the program this semester and haven't been able to attend any of them, but our AEG members head down to NC for the AEG meetings. I'll probably make my way down to some of them next semester for some networking.

You do much rockfall/landslide investigation? That's my main interest at the moment, in conjunction with geophysics.

 

[avodude]

You guys back east and your sedimentary rocks! Haha. Those aren't grains! They are crystals! Probably plagioclase feldspar. That is a porphyritic igneous rock. Look at the geologic history of Alaska. It is nothing like the Appalachians. In the Northwest, we have basalt or granite as our bedrock and sandstone is rare. It is common to see a rounded basalt rock like the one pictured above, here and in Alaska. I'm also assuming that he was in coastal Alaska which has some of the highest iso-static rebound in the world and was scoured by glaciers. Most sedimentary deposits are long gone unless you look offshore on the shelf. Uplift intensifies erosion. Look up accreted terranes and subduction zones. Might get some marine deposits from an accretionary wedge, I guess but volcanics are huge in Alaska. Totally different than what is happening in the eastern US. Anyway, not trying to offend you guys but you should come out west, especially NW and Alaska and check out the geology out here. You guys are sedimentary masters, no doubt, but you should check out the igneous and metamorphic rocks out west.

 

[avodude]

Or in New Zealand. mallacootasmoothie has some good examples of igneous rocks above. Igneous rocks are also classified by their crystal size (fine grained phanerites for example versus porphyritic). The rounded rock from a pothole is much more fine grained than the large crystal (I'm guessing grano-diorite) type rock it is sitting on. Both are igneous rocks and definitely, without a doubt, not sedimentary.

 

[mallacootasmoothie]

Thanks for the interest in my rock, great to hear some professional opinions about its origins.
From my limited understanding it is not a sedimentary rock, it is much harder than sandstone (or the sandstone I've seen.)
I would not be able to scratch this rock easily like sandstone.
I found it in a bowl shaped hole, on the south east coast of Australia while fishing for wild bass.
I actually looked at the hole and how it was spherical inside and thought something must have spent a long time rumbling around in there to carve out that bowl. The opening at the top was about 12" and sphere at its largest diameter was about 20", I wish I had a photo of it but I don't.
When I looked closely into the bowl I saw the round rock in the bottom. The river bed where I found it usually only floods every second year.
I left the rock in the hole and hiked back in a year later with a framed pack to haul it out.
I placed a remotely round rock back in the hole just because it felt like the right thing to do.