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TOPIC: MO Rhyolite, A Brown,Reddish & Purple Material

MO Rhyolite, A Brown,Reddish & Purple Material 1 year 1 month ago #94366

  • JoshinMO
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Have created mo rhyolite threads a few times, tried a couple pics earlier though and maybe they are better than before though my camera and or cam. skills doesn't show material well enough and almost seems like people would have to see in person. Its Brown yes but its also a dark reddish color and has a purple "hue". The sunlight brings out the purple and its a bit overcast in pics from clouds but any brighter makes the pic bad. It is an igneous made material and comes from the area of the highest point in Missouri (st. francois mountains) in the eastern ozarks. There has been points made of this material travel over 50 miles and even further almost into arkansas.

Some pics and links.
101_0843640x480.jpg


GEDC1132640x480.jpg

ST Francois Mountains/wiki
Rhyolite link
I call it a kaiser blade, mmm
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MO Rhyolite, A Brown,Reddish & Purple Material 1 year 1 month ago #94420

we've got a good amount of rhyolite here in narragansett bay too, mostly the brown and reddish kind. but theres also a few differant colors here im told, i never find any though...
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MO Rhyolite, A Brown,Reddish & Purple Material 1 year 1 month ago #94424

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Neat, yeah colors/shades vary a little also. Even seems some artifacts made of it are grey. Not an easy material to Knapp but strong.
I call it a kaiser blade, mmm
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MO Rhyolite, A Brown,Reddish & Purple Material 1 year 1 month ago #94464

  • SevenOut
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If you do not have a geological map of the area, let me know and I will try to find one in my library to scan your major "igneous exposures" and post it. People probably would not believe that granite is also in SE Missouri. It is and I have been there, too long ago but in the same area you mention.

Rhyolite is related to Granite as Obsidian is related to Basalt. Rhyolite is silica rich. Basalt is silica poor. Silica is the basic mineral that makes up chert, flint and agates, which also form differently under different conditions. Whew.... Different mineral content can influence weathered surface colors or the entire flow. There are no rules when it comes to rock appearances. OK, some, but the books are very thick with words that you need a dictionary to look up and the experts argue about it all the time.

Both Rhyolite and Obsidian were cooled very quickly. Quickly is a relative term as it varies from place to place, even in the same area! If Rhyolite did not cool quickly, it would have crystal growth and be like Pikes Peak Granite over millions of years of cooling beneath the surface. At times you will find crystals that developed and found in Rhyolite as the temperatures fluctuated below the surface and are easily seen in your points. The inclusions will indicate the flow that the material was found by a local geologist... if any.

Is there one quick answer to what Rhyolite/Granite or Obsidian/Basalt are? Nope...never will be and increases in one component versus another... and it has various local and petrographic names. Under a microscope a mineralogist can tell you where the material came from... if they work in that State or area! The rest of us just plug along and, like yourself... know Rhyolite and its family well enough to point it out to the rest of us!

Rhyolite is found much like Obsidian where the quality varies... A LOT. For Rhyolite, having a higher percentage of Silica makes it very good to Knap, but dulls quickly. The lower quality of Rhyolite is similar in color, but dull and powdery surface. The "hard" Rhyolite is glossy and resists weathering and deeper in color. The soft Rhyolite will quickly become mud, silt and little crushed stone quickly... like that used in my road to the storage building. The hard Rhyolite is also used, like in the Denver, Colorado area, as a building stone in the 19th and early 20th century buildings. Depending on which quarry the Rhyolite came from makes a big difference in how it stands up to weathering. Some found out a bit too... late.

Basalt is usually black and can be in the rusty brown reds. Even basalt when it is not full of air bubbles can be hard and used to make rougher tools, like flaked axes in the Southwest. See it in New Mexico all of the time when agate hunting.
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MO Rhyolite, A Brown,Reddish & Purple Material 1 year 1 month ago #94474

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Josh nice looking material man. Seven Out If you have a map please by all means post it. As long as it does not show secret hunting spots and such. If you were to show us a Map like that the nexty time afield you might find something you weren't looking for. Someone elses foot prints.
Just cuz you're paranoid don't mean they ain't out to get you
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MO Rhyolite, A Brown,Reddish & Purple Material 1 year 1 month ago #94482

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Hoss wrote:
Josh nice looking material man. Seven Out If you have a map please by all means post it. As long as it does not show secret hunting spots and such. If you were to show us a Map like that the nexty time afield you might find something you weren't looking for. Someone elses foot prints.

*********
I know what you mean. I have found other's footprints at some of my best field hunting sites... and they were not livestock nor deer! Sometimes you just do not get up early enough.

This a scan of part of the map for SE Missouri that has the Granite and Rhyolite locations. If you stop at one of those Granite Quarries it gets my knees shaking as they are some deep pits. The huge blocks sitting around give you the impression that you need no guards to keep someone from carrying anything off the property.

The Rhyolite areas are colored brown. The Granite areas are reddish. There are some spots that are outside of the scan I could make, but this is the center of activity. The book is authored by E. R. Buckley and H. A. Buehler called The Quarrying Industry of Missouri (1904). If you are near the former Rolla School of Mines... the library will have a copy and they might even have originals for sale at the Geological Survey there. You can find this same Granite near St. Louis... but you need to dig a hole more than 3,600 feet deep to get to it.

Rhyolite makes up the majority of igneous rock in the area and the early geologists recognized two kinds of Rhyolites- porphyries proper and porphyrites. And that is where you can get to work.

Josh has done all of the SE Missouri collectors a favor by illustrating Rhyolite artifacts! I am sure that in a short time ground Missouri Granite artifacts can also be tracked to this area of Missouri. Although the glacial moraines on the north side of the Missouri River were an option for hard stones and quartzite for metate and mono's drifted in from Minnesota, of all places. Now when Josh pulls out some strikingly beautiful point of hard Rhyolite... he had better watch for tracks in those fields!

I am sorry the scans are not better, but it is better than having me painting a picture. There is also a Missouri Archaeological Survey book that lists the majority of ancient flint and chert quarries in Southern Missouri. I just cannot recall the title or if it can be found around here without suffering a stroke or something serious, like a paper cut.
Scan1.jpeg

Scan_2013-08-13.jpeg
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