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Post by 150FromFundy on May 4, 2009 21:33:17 GMT -5
On my recent trip to McKay Head (previously posted), I managed to collect a wide range of various types of Rhyolite. Personally, I think Rhyolite does not get the attention it deserves in comparison to the Agates and Jaspers that we are more familiar with. Truth of the matter, there is almost as much variation in Rhyolite as can be found in Agate and Jasper. I wanted to learn a little more, so posted what I found out along with photos of my recent finds. If your not interested in geology, you can skip over the next paragraph and go straight to the photos. Did you know that Rhyolite is a volcanic (extrusive igneous) rock that has essentially the same composition as Granite. Unlike Granite that cools slowly deep within the earth, Rhyolite flows to the surface of the earth in lava flows where it cools quickly. Both Granite and Rhyolite are mainly Feldspar and Quartz with some Biotite (mica) and Hornblende adding the dark components. The overall composition of Rhyolite is silica (70% - SiO2) which allows the rock to take a polish similar to Agate and Jasper. Rhyolite may be glass-like (obsidian), flow banded, porphyritic, or brecciated. Along contact zones and faults, where some metamorphism occurs, interesting combinations occur. All these samples were collected along a one mile stretch of beach. The combinations and variations are due to these Rhyolites being formed along a contact zone with faulting. Photo 1 – Banded Rhyolite (Tiger, Tiger) Photo 2 – Banded Rhyolite (Jade Garden) Photo 3 – Porphyritic Rhyolite (Paint Spatter) Photo 4 – Brecciated Rhyolite (Dog's Breakfast) Photo 5 – Agatized Rhyolite (Lime Ricky) Photo 6 – Complex Rhyolite (Brecciated and Obicular) Photo 7 – Complex Rhyolite (Fractured and Agatized) Photo 8 – Complex Rhyolite (Flow Banded and Swirls) Photo 9 – Complex Rhyolite (200 million year old Intrasia) Photo 10 – Picture Rhyolite (well almost a picture) Happy Rhyolite Awareness Week! 150FromFundy
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Post by Michael John on May 4, 2009 23:18:11 GMT -5
That's an absolutely wonderful presentation! Thank you!
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Post by Woodyrock on May 5, 2009 0:20:41 GMT -5
What a great collection of great looking rhyolite! If you can get a polish from it, theses will be every bit as good as a jaspers, and agates. Most of us like wonderstone, but this material is better. Woody
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Post by frane on May 5, 2009 9:28:10 GMT -5
This is a very nice post! What a variety you collected! I love reading and learning about the formations also! I sure hope you can get some good cabs or tumbles out of them! Fran
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nancyid
has rocks in the head
No stone goes unturned.
Member since January 2009
Posts: 563
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Post by nancyid on May 5, 2009 9:48:36 GMT -5
You certainly have my attention! You have me wondering why your Rhyolite is so cool, great colors and patterns. We have lots (mostly) Rhyolite in the local rockhounding areas here (basalt also) But our Rhyolite is just plain red to brownish red. Should I be checking it out closer? Is it because your's is older? Because of whatever other minerals are in your area?
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Post by stonesthatrock on May 5, 2009 10:26:09 GMT -5
ty for the post
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on May 5, 2009 10:30:01 GMT -5
Thank you for this! I absolutely love Rhyolites.......an endless array of colors and patterns, as you have shown.
Shannon
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Post by mohs on May 5, 2009 11:41:35 GMT -5
i liked the geology write up and the display are picturesque that lime is my thing excellento !!
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Post by 150FromFundy on May 5, 2009 13:28:46 GMT -5
To all, thanks for the feedback and encouragement on my posts. Understanding a little bit about the geology behind the rocks has vastly improved what I find.
Nancyid asked about why there is so much variation in the rock. To put it simply ... we are geologically blessed. The Bay of Fundy is an ancient rift valley. The continental plates ripped apart and the sea rolled in forming the bay. As the plates ripped apart, lava flowed out forming thick layers of basalt, rhyolite, and other volcanic rocks. This didn't happen once. There is evidence of many lava flows over time. Every lava flow has a slightly different recipe for rock.
To further complicate matters, the area is covered with both major and minor faults. These faults, when active, open up cracks in the earth for more lava to gush out, forming dikes and sills of different material in the original bedrock. Every flow has a slightly different recipe for rock.
To further complicate matters, some metamorphism occurs along the plate boundaries. Metamorphism changes rock through extreme heat and pressure creating more variation. A little like baking agates for color change.
To further complicate matters, the area was heavily glaciated. This is where the land mass glaciers met the ocean and dumped all kinds of transported material in moraines and till deposits. Much of the rock we find was created hundreds (or thousands) of miles to the north from the Precambrian Shield (Canadian Shield).
There's not an easy answer to Nancyid's question. It's rather complex, geologically complex that is, but it makes for great collecting.
150FromFundy
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rockerfellerz
starting to spend too much on rocks
Member since August 2008
Posts: 120
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Post by rockerfellerz on May 5, 2009 16:53:15 GMT -5
Fantastic stuff you got there! I mostly look for the agates and jaspers, but I'll be on the lookout for some of that! I plan on visiting some new places around the Bay of Fundy this year. The slab in pic 5 looks something like the rock in pic 13 of my latest thread in the tumbling section.
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rockhunter
off to a rocking start
Member since May 2009
Posts: 10
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Post by rockhunter on May 5, 2009 18:15:55 GMT -5
Wow! That is quite a collection! Thanks for sharing it. This was my first thread viewed here and I am impressed.
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Post by Michael John on May 5, 2009 19:39:02 GMT -5
150, I'm near a different but oddly similar geological phenomenon, Death Valley, which is studied by people from all over the world due to the extreme geological events which have all occurred in this relatively "small" area over time. Although there's no hounding allowed within Death Valley state park's borders, almost all of my hounding is within 10 miles of the borders.
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Post by 150FromFundy on May 5, 2009 19:56:10 GMT -5
MJ
One of the things that amazes me as I read more into this geology stuff, and follow the RTH posts, is how similar some of our material is. I have seen posts from weeshan, saskrocks, and now one from the UK of material that I could have collected on a Bay of Fundy beach. You should post a little geological interpretation from your next trip. I think this may catch on.
I guess when it comes down to it, we were all once part of the same supercontinent ... Pangaea.
150FromFundy
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Post by Bejewelme on May 5, 2009 20:03:48 GMT -5
Your posts are always, well written, well photographed and super interesting! And in this one in particular, I love the names!!! What an incredible array of varied material, so beautiful! Thanks for highlighting another find in your neck of the woods!!! Amber
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nancyid
has rocks in the head
No stone goes unturned.
Member since January 2009
Posts: 563
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Post by nancyid on May 5, 2009 21:18:54 GMT -5
150FromFundy, thank you for acknowledging my questions. It is complicated but fasinating. Thank you.
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Saskrock
fully equipped rock polisher
Member since October 2007
Posts: 1,852
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Post by Saskrock on May 5, 2009 22:22:01 GMT -5
I wonder if some of the glacier stuff isn't from the same spot as well as looking the same? As I understand it the glaciers started in the Hudson bay area and pushed out South, East and West. If you lookat our locations on a map in relation to Hudson bay its right in the middle and North. Could we both have a bit that started up there? What do you think 150FromFundy?
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bouldergal
freely admits to licking rocks
Glacier Meadow
Member since July 2007
Posts: 783
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Post by bouldergal on May 6, 2009 17:15:46 GMT -5
Thank you for adding to my limited geological knowledge base. I hear so many names of rock that so many of the "Rock Gods" all know on sight and by name. I wish more of the members would post information like you did. Knowing where something comes from, why it's specific to that location, it's hardness & composition, etc. makes the entire hobby a lot more fun. Your post was wonderful......I LOVE what you're finding.
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adrian65
Cave Dweller
Arch to golden memories and to great friends.
Member since February 2007
Posts: 10,786
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Post by adrian65 on May 6, 2009 23:43:10 GMT -5
Very interesting, thank you for sharing the pictures and the knowledge.
Adrian
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