2018 Geology Rocks Talk





And lastly, shiny!!




Again, all the silvery places are lifted up areas of feathered-papery pieces. It’s really pretty. These are on the opposite side of the reddish-brown (iron?).

Whatcha think?

Be kind. This is the first time my rocks have been out in the public eye. LOL I’ve had both for maybe 35-40+ years.


I got the big rock from the top of this place, The PA Grand Canyon, probably from a spot on the west rim… somewhere. LOL


My preliminary opinion is that is Late Devonian, Early Mississippian age shale and sandstone layers. I’ve got a good paper from the Pennsylvania Geological Survey. I’ll post it with an explanation in the next few days.


The large rock doesn’t have any breaks, even after moving it through 4 states. No evidence that it would sheer off into thinner pieces. The most it does is leave a tiny amount of rock “dust” when moved (like shown in one photo).


A friend came over tonight. She said that big rock has to be 15 to 18 pounds… She agrees with you it has shale, but it’s unlike shale I saw from coal mine roofs in SW PA. Of course, PA Grand Canyon is anthracite coal. She agrees with me that it has little to no apparent sandstone. But neither of us are geologists.

Said the small one looks / feels like marble.

I wish I could bring them to you @kateg so you can officially Name These Rocks!


Just call em “Kitty Stones”. :smirk_cat:


Never thought of that!


And that’s “KItty,” not “Kidney!” :rofl:


I need to think about this more. I believe not all shale is friable (crumbly). I’ll need to pull out some of my geology textbooks this weekend.


That’d be great! Kind of like sending off DNA and all excited to find out where your rock family comes from… LOL


Cagey Cat’s rocks:

Rock diagnosis made with help from kateg’s mom (also a geologist, who grew up in western NY and went to undergraduate university at SUNY Binghamton for geology).

Disclaimer: a more definitive analysis should be sought from a geologist who can look at the rock in person as it is difficult to be certain on rock ID from photos.

Location of rock: the Grand Canyon Of Pennsylvania, western rim

  1. The larger rock is a metamorphic rock. It does not have the appearance of shale or sandstone. Also, there is presence of mica, which is the shiny paper-sheet-like mineral. This mica appears to be part of a low-grade metamorphic rock (mica appears on its own before the schist and gneiss phase of high-grade metamorphism), so it must have undergone some high pressure and/or high temperature to form. This rules out its origin as part of the Mississippian sandstone/shale sequences native to the western rim of the Pennsylvania Grand Canyon (see attached geologic map)
  2. So where did it come from? Maps of glacial extent show glaciation reaching the eastern rim of the canyon in glacial extent maps (see attached glacial extent map). The rock is found in a region close to, but not within, this glacial maximum extent. The only way you would find a metamorphic rock on the western rim is if it had been brought in from glaciers originating in the Canadian Shield. This indicates that it was probably brought in to the park as building material for the trails (were you near the trail?). It could have been brought in by trucks from the nearby glacial materials found to the east of where you were. The smaller rock also does not appear to be from this area either and was probably part of the same human-transported glacial material as the large rock.

Below are links to articles from the Pennsylvania Department of Conservation and Natural Resources on historical glaciation in Pennsylvania and the geologic history of Pennsylvania. They include the glacial extent map and the geologic map I have posted above.

“Pennsylvania and the Ice Age”, published in 1999


“The Geological Story Of Pennsylvania” published in 2014



Aha! Justification for my playing with rocks when I was little. :rofl: I was always interested in rocks - the different types, colors, etc. - and made a lot of trips to the New York State Museum to look at their rock collections. I loved those that were luminous under ultra-violet light. They had a room where you would draw a curtain and the UV lights would come on and what a bright colorful display. I guess my interest in rocks was carried all the way to when I was working and got to “play” with them in some stone quarries (on my lunch break of course).
Now I’m going to have to research the types of rocks in my area. :smiley:


I’m still trying to digest your lovely maps and chats.

First, thank you and your mom for going to all this trouble to ID my 2 “Special” rocks.

Like my time here on Tomnod, my imagination ignites about my rocks. So they have lives and personalities (well, at least they do to me!). They are excited to be originally Canadian, possibly coming down from ‘the Champlain Lobe of the Laurentide Ice Sheet’. Even if I’m not quite right (lol @Jim7 stop it!), the name sounds pleasing to the ear. :smiley: .

I admit, I forgot all about glaciers. I thought more about the Appalachians and how geologists think those mountains were formed and shaped by both millions-of-years old volcanoes, now long dead, along with folding and stretching. When I leaned toward metamorphic rock, I thought of high temps, not ice weight and pressure. In my wildest imagination, I thought of a (now long extant) volcano back then spitting out rocks willy-nilly and with land-spreading that my rocks just happened to land on the top of the western rim of the PA Grand Canyon. Well, those were my uneducated, romanticized geological stories I wondered in my head.

The whole idea of human transport makes my rocks sound… less glamorous. (Why isn’t anyone investigating “Rock Transport Rings”???) Back in the early 1980s, I wouldn’t have called the “trails” anything but glorified packed dirt with some pebble-gravel on some places. The rock was under soft soil, under trees, well off the path. The bigger rock is too big and too heavy to have rolled anywhere, like from a pathway. But however it got there, it’s still a Canadian rock that rode a glacier, and ended up hidden and buried under the shade of a tree. I think the best story is that its little mica wings formed on its way into Pennsylvania and so, the rock “flew” to its resting place where I found it.:fleur_de_lis: LOL

It would be interesting to take the rocks to a University for a thorough “physical”… but I doubt I can do that now. I doubt I could carry the dang thing from the parking lot to the building! Besides, the big rock is quite happy to be Canadian from ‘the Champlain Lobe of the Laurentide Ice Sheet’.with many mica “wings” that helped it “fly” to where I found it. (Shhhhh… we just won’t mention that big trucks could have made it “fly”.)

I know, I’m silly.

Thanks big bunches for studying the pics, and for all the detailed explanations! Here, I thought I had a hot rock, but really, it is just a really cool rock. hahaha

P.S. (By the way, my Grandpap drove trucks carrying quarried rock from western PA up to the PA Turnpike when it was being built. After they blasted through the mts, he trucked that rock after it was broken up to the eastern side of the Appalachian Mts where they laid it as the road foundation, and built up the runaway truck ramps along the highest portions of the highway.)


Sorry, (I wasn’t clear about that part) but the metamorphic rock would have formed by heat and pressure at depth in the Canadian Shield region and was then brought to the surface by some tectonic process (folding, faulting, erosion of rock above it. I am not familiar with the origin of metamorphic rocks in that part of Canada. That metamorphic rock would then be captured by a glacier and dragged all the way to PA as the glacial extent advanced southward and left behind when the glaciers eventually receded.

I think the mica would have formed before the glacier dragged it. I don’t think the glacier has enough pressure to form the mica even though mica is low-grade metamorphic. I will need to read more about metamorphic rocks formed in Canada and about conditions for mica formation and get back to you. So this is still an investigation in process, I will get back to you on what I find (seeing as I am furloughed for the time being :grin:). Your rock will be happier if it knows you better understand it :grin:


Hey! That’s my 5-year old granddaughter’s middle name - minus the “tide.” Of course I’m not laughing… hysterically… :laughing:


I found my scales…

Big Rock with mica wings = 11.2 pounds I thought it was heavier. Sure is dense. All I kept praying when I lifted it was “Don’t drop it on my foot-- either foot! It’ll break my toes!!”

Small White Rock = 3 solid pounds

Me … not telling. LOL


How you faring @kateg ? Haven’t seen you pop up in emails. :frowning:


I keep hoping this will get resolved. We have savings and my husband’s income until I get back pay. I am worried about the huge number of people who are running out of savings, or have already ran out and will miss another pay check on Friday. I have never donated to a GoFundMe campaign before, but this week found some furloughed employees who need help for bills and contributed to their campaigns. I wish there was a way to “Tomnod” this issue!


New York state and a group of private businesses have joined forces to provide interest-free loans to furloughed federal employees in this state to help out until they get paid. I’ll check GoFundMe and see if I can find that link. (Or maybe you can PM me with it? :wink:)

Edit: Where are all these billionaires out there? But I imagine if they were to step in and “pay” everyone, then the shut down would just continue a lot - a very lot - longer.