Deleted
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Post by Deleted on Jul 9, 2013 10:50:08 GMT -5
I went to a dudes home last night to buy a saw. Turns out I knew the guy from lapidary class, but that's another story. He has 20 tons of stones in his yard and what seems to be nearly a ton of montanas. He said something about them being petrified wood, so I inquired further. He dug out a couple of pieces to show me that indeed it is petrified wood. Judging by the two pieces he produced that were both clearly montana agates and petrified wood, I had to agree. He mentioned a geologist names Wright. This morning I did a bit of googling. I found this website.That says (among other things) this: I thought this was very interesting and wanted to share. |
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Geoff
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Post by Geoff on Jul 9, 2013 11:39:46 GMT -5
Huh. Thats really interesting. I'm guessing you weren't able to take any pictures?
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Post by catmandewe on Jul 9, 2013 12:28:37 GMT -5
I have some Montana agates that are definitely pet wood also, most of them have been river tumbled so long the bark has been removed but occasionally you can find some that still has bark on it.
Tony
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gemfeller
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Post by gemfeller on Jul 9, 2013 12:45:40 GMT -5
Thanks for posting that Shotgunner. I grew up not far from Yellowstone, and the effects of the fearsome Yellowstone Caldera are seen nearly everywhere. Entire forests were engulfed and burned up by the hot lava from the eruptions. They often left "molds" in the rock that were later in-filled by water-borne silica. The Harmons, who are experts on the material, tell the story better here: www.harmons.net/Montana_Agate.html |
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grayfingers
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Post by grayfingers on Jul 9, 2013 12:53:03 GMT -5
Scott, I live in the the area described in your article. I have found limb casts (small stick) that are agate, and sorta nodules that are mostly clear agate that one can see from the skin were once wood. I believe that when wood is encased in hot lava, sometimes the wood burns off and leaves a mold. Most Montana agate nodules I have found were formed in air pockets in the lava. I believe that when wood is buried in mud/pyroclastic flows, depending on many factors and the amount of available silica rich ash, some wood is replaced by chalcedony/agate. I hold to the theory that Montana agate can be anywhere between 10 and 60 million years old. I have several examples of agate wood, will look for them. These cabs are wood that became agate, found on the Yellowstone.    Another tumbled piece  |
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Deleted
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Post by Deleted on Jul 9, 2013 12:57:37 GMT -5
Geoff, I went to buy a saw. I wasn't expecting to get a lesson! I plan to pick up the saw next week. Maybe then I can get an image. It's just a small portion of the skin that is obviously bark/wood as Tony describes.
Bill, thanks for sharing your images.
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Post by deb193redux on Jul 9, 2013 13:03:31 GMT -5
Small world, I know the guy, Marl Ralston, who wrote that web page. I met him in the Nittany Mineral society when I was at Penn State. Going to his house was a trip. He has collected tons of high-quality Montana agate in the course of several river trips a year every year for almost two decades.
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Fossilman
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Post by Fossilman on Jul 9, 2013 13:33:37 GMT -5
I've hunted the "Yellowstone" a few times,but my Nephew hunts agates and petwood there all the time,I'll have to ask him about some weird agates he finds....
Cool news.Thumbs up
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Post by orrum on Jul 9, 2013 18:59:34 GMT -5
Hey Daniel I spent a lot of time in State College soaking up Rolling Rock beer in the Rat Skellar while you were there. I went to Va. Tech but dated a Nittant Lion volley ball player. Small world.
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Deleted
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Post by Deleted on Jul 9, 2013 21:23:53 GMT -5
I love that you dated a Lion!
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panamark
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Post by panamark on Jul 9, 2013 23:13:22 GMT -5
I am of the opinion that a huge amount (maybe the majority?) of montana agate is from pet wood. I, like others, have lots of pet wood from WY and MT that can be broken and tumbled and you couldn't tell it from any other "montana agate".
One other thing - as far as I know the 2 different major episodes of volcanic activity of Yellowstone prehistory were pyroclastic, meaning it was hot ash, not flowing lava. There were some very small lava flows, but the stuff that made the pet wood was all pyroclastic, burying the wood "safely" below many feet of ash so they could very slowly be replaced by silica instead of rapid decomposition. Lava flows pretty much burn everything in their path I think, so pet wood isn't formed this way. Just my amateur geology 2cents. -Mark
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Fossilman
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Post by Fossilman on Jul 10, 2013 10:05:28 GMT -5
I have a small rock from the Yellowstone,its half petwood and half agate,pretty cool looking...
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Post by rockpickerforever on Jul 10, 2013 10:34:21 GMT -5
Check out the last pic in Geoff's thread here. Although lines in rocks can be caused by many things, this certainly could have started out as wood. I agree with the Montana Agates = Petrified wood premise. Jean |
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Post by johnjsgems on Jul 10, 2013 13:14:42 GMT -5
I vote more likely limb cast than mineral replacement. I don't remember any knots or growth rings evident other than small areas of banding.
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gemfeller
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Post by gemfeller on Jul 10, 2013 13:48:27 GMT -5
I agree with John but I've seen some specimens that exhibit features of both mineral replacement and of casts. I can't get the infernal Linky thing to work but this website has some excellent examples of Montana agate casts: www.risingsunwholesale.com/limb_cast_agate.htm |
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Deleted
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Post by Deleted on Jul 10, 2013 13:51:48 GMT -5
I agree with John but I've seen some specimens that exhibit features of both mineral replacement and of casts. I can't get the infernal Linky thing to work but this website has some excellent examples of Montana agate casts: www.risingsunwholesale.com/limb_cast_agate.htmThat link is spot on topic! Thanks for sharing. |
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Fossilman
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Post by Fossilman on Jul 10, 2013 14:06:45 GMT -5
Dang that site is off the hook cool!!!!!
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bhiatt
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Post by bhiatt on Jul 10, 2013 15:51:22 GMT -5
here is my river tumbled montana petwood limbcast with built in thumb hold so you dont drop it. I think thats the right description.  |
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Deleted
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Post by Deleted on Aug 22, 2013 13:24:55 GMT -5
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Fossilman
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Post by Fossilman on Aug 29, 2013 10:48:17 GMT -5
So in reality,most Montanas are limbcast petwood??? I see alot of Montana agate just as they show in that site.....I probably have a bucket full in my shed like them too.......
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