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Here is some of the Rhyolite points found in my site and the effect of the acidic soil on the material. The one that is the most deteriorated has flakes of it on left side on napkin where it has flaked of more after I washed and it dried. The small point is older than the other two and was effected the less by the soil. 
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South East Ga. Twin City -
Chert in FL sand will do the same and become chalky, sometimes obliterating work/wear. Usually the oldest stuff. Even "experts" have to look carefully.Professor Shellman
Tampa Bay -
I've noticed that a lot of my older points don't turn that white chalk color. Guess some rhyolites don't degrade as much as others.Seems like the Savannah Rivers turn chalkey more then others. I know a lot depends of the soil makeup as well. I believe there is some older threads that mentioned rhyolites with a higher silica content don't change form as much. Great topic Willjo.N.C. from the mountains to the seaComment
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Johnny I can’t tell you how valuable this information is my goodness . Your being in my neighborhood to . We soil test and this explains so much . High acid !!!
I have several that are like that .
Some are lime deposits I know but wow this brings a new
conversation to the table for my group and I thank you for that .Comment
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I'm always curious about stuff like this, good thread.Comment
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Hi folks,
This is a really interesting subject and I don’t think there’s a simple answer. Here in NC I have found black and chalky looking points in the same field along with bi-colored points. Most all of the Guilford’s are chalky but older Palmer’s can be black? It’s weird because we all know the Palmer’s are older. I think it has to do with the quality of the material. The older points were made from better material and hold the original black color. Here’s a picture of a bi-colored point.
I didn’t see his post but I agree with Sugaree. The older the point the more likely it is darker colored rhyolite.
VonLast edited by Von; 03-28-2018, 08:40 PM.Comment
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While soil Ph and the approximate age of a lithic artifact are factors that need to be taken into account, the key to understanding the stages and rates of deterioration in a particular lithic is to know what minerals are present in the whole of the lithic and the variations those minerals can produce.
Rhyolite has a mineral content that is - groundmass generally of quartz and plagioclase, with lesser amounts of orthoclase, biotite, amphibole ( augite), pyroxene ( hornblende), and glass; phenocrysts of plagioclase and quartz, often with amphibole and / or biotite, sometimes orthoclase. The presence or absence of these minerals at the time the rhyolite was formed is what determines what kind of rhyolite is formed. Rhyolite that is comprised of mostly grainy quartz, called groundmass, will deteriorate faster bc it lacks the minerals needed to make it a more solid type of rhyolite, while rhyolite with a high amount of pyroxene creates what is known as hornblende which is harder and deteriorates slower. The different minerals also affect the color of the rhyolite and coloration can give you clues about what you have.
As to the three pieces presented at the beginning of the thread, I would venture to say the darker piece is likely hornblende(dark green-black with greenish banding), center pieve looks like it is a tighter groundmass with plagioclase present, far right appears to be mostly groundmass with a small amount of plagioclase and almost looks pumice like.
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Rhyolite Flakes different, what I hear. Nice Point's!Comment
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No kidding, I took a couple swings with a hammer on some and was thinking wow. A knapper I know doesn't really reccomend it either as I asked Him how it was and He said like Concrete. Crystal's in It/unpredictable but another Guy acted like It was easy but I don't remember any fine Point's He made out of It. But there are some nice Rhyolite Point's.
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