Agates, Onyx and ancient cave questions...

[Phil Winkler]

The above article is from http://mdc.mo.gov/ and is an excellent site. Searching for cave their reveals hundreds of articles many by Bill Elliott who many of us know.

[bigalpha]

the different colors, I believe, come from different compositions. For example, a trace element can change the color from clear to blue (hydrated copper) or clear to grayish (Lithium, I think).

[Teresa]

From a Mo web site:

Geologists are unsure exactly how the chert formed in the limestone. Two possibilities are that oceans deposited silica along with the calcium carbonate shells of marine life, and the chert formed into sedimentary rock along with limestone. Another theory holds that chert formed later, when silica-rich ground water permeated spaces in the limestone. Whatever its origin, chert exists in limestone, and chert nodules, veins and layers are easy to see in road cuts through chert-bearing carbonate rocks.

The above is messed up. There ARE four different ways in which chert is formed.
1) As primary deposits on deep sea floors beneath the carbonate compensation zone (zone where calcite/limestone does not form due to high levels of CO2. These chert layers are the sort which are exposed near San Francisco--interlain by shales and sandstones and other silica based rocks.

2) As an agglomeration of essentially silica gel, forming being attracted to seeds of undissolved quartz or even organic matter (both carbon and silica have the same chemical valence of+4) at low temperatures, which then compresses into rock simultaneously with the formation of the limestone.

3) As a replacement of silica rich pockets of limestone or dolostone, after reimmersion in silica rich seawater. You can see the layering of the sedimentary rock in the limestone continue into the chert,and back out again in adjoining rock layers. This is the preseumed origin of chert reefs-- the reefs were originally limiestone,, but trapped silica and sand as they formed. This inherent silica then formed chert after reimmersion.

4) By hydrothermal means-- silica cooling from volcanic or hotspring or geyser activity. Thundereggs,and other volcanic cherts and agates like those in Michigan and Oregon formed this way.

The banding and color in agates forms simply because of differing silicic water intrusions with different water chemistry.

Although the Missouri Dept. of Conservation has an excellent site for biology and living things, rocks and minerals DO NOT fall under their area of expertise or responsibility -- that is under the Missouri Dept. of Natural Resources-Division of Geology and Land Survey. I suspect this article was copied from the state handout on chert done by the DGLS.

[Teresa]

In the case of chert and other rocks, iron is the most common coloring agent. Iron can color rocks pink, purple, red, orange, rust, brown, black, green, yellow and blue, depending upon what other chemicals are present.

Naturally, other chemicals can result in other colors, but color alone is not a way to identify any coloring agent .
You gotta test for the chemical. Usually coloring agents are metals or semi-metals...or positive ions, at the least

[hewhocaves]

John, the whole place is littered with small caves and rock-shelters. Not as many as there are when you really get into the far NW reaches of Georgia, but enough. When my dad had his well drilled they hit several voids, not that means much. They still had to go 300' before they hit water. But my brother says there is a shelter with a "crack" in the back that seems to go - breathes a little too. HA! So we set off down the hill and after about 20 feet I realized I am covered with ticks. Dads yard is the white-tail superhighway. You know how much I hate stinging sucking insects. I'm gonna wait now until after a hard freeze. That cave isnt going anywhere He says its not big enough to fit through, so if it looks like it goes, I am gonna need a digger.

right... so get to digging! come on... now... now.. quickly! quickly!! LOL

That well report is good news. Don't worry about not hitting a void - you just missed the cave passage, that's all. What is good news is that you have 300 vertical feet from the well point to the water table. that's plenty for a couple levels of cave (pits not included, some assembly required, offer void in Louisiana). Is the water table flat(ish) in that area?

waiting till winter, btw, means that you should go looking for warm spots and steam. Clear a path and then dig it out in the summer. (it's much easier to surface walk in winter than summer, anyway). Waiting till winter also means you might want to consider the freeze-thaw cycle and look for loose rock in those shelters.

I'm sure this is all known to you already. Tune in next week when I explain how to put shoes on. (tgif)

John

[graveleye]

well, I'm terrified of digging actually, which is why I'll have to rely on the lunatic fringe to open that sucker up...

I wont be surprised if it does go somewhere, but this aint like classic TAG area. Most of the caves around there dont go far, and I've yet to see any big pits in any of them. But hey, there is always a first eh?

This is sort of why I started this thread though. I still feel though, that the area used to have more caves, but they're just eroded away. I can almost see it in the lay of the land. But, like I said, I'm no geologist, just a nut with a big imagination.

PM me if anyone wants a piece of pretty polished chert in the next few months

[wendy]

i'll come help dig once the ticks go away

[graveleye]

you are more than welcome to participate!

Thanks for your help everyone. I'll post some pictures of some of the stones when they are nice and shiney!

Kev

[bigalpha]

yes! shiney rocks! I'm in.

Teresa -- while you cannot definitively say that the coloring of a rock is from one element/cation -- can you say that it's most likely from a certain element/cation? Or maybe, from a higher concentration of element/cation than other impurities?

[Hatch]

What's a good model rock polisher to look for? I've always wanted one and now that I'm all grown up at age 38 I think I want to get one.

P.S. Just kidding...I'm not really grown up. Just ask my wife. Heh.

[graveleye]

What's a good model rock polisher to look for? I've always wanted one and now that I'm all grown up at age 38 I think I want to get one.

P.S. Just kidding...I'm not really grown up. Just ask my wife. Heh.

HAHAHA!!! Dont feel bad. I just turned 40. I begged for a rock tumbler allllll my life and Santa never brought me one. But Mrs Graveleye finally heard my childlike pleas, and bought me one!

In fact, I believe that its probably best that I didnt get one when I was young. It takes a LOT of patience because the process takes a long time. Even now, old and wise ( ) I have to resist the urge to hurry the process.

There are several mfrs out there. They make some that rotate and some that vibrate. I really dont know which does it better, but since I have a rotating one, I like them better

Mine is a Lortone. Dont buy one of those little toys at the hobby shop. They wont last long and dont hold barely any stones. These machines are designed to take a beating... they literally run 24/7 for months and years. The starter kit can be bought for around $70 and usually comes with a bag of agates or something, and enough grit for about 4 batches. I got the 3lb one, but I want a larger one now. They sound like rain when they run too... mines in the garage, doesnt make much noise, but you wont want it in your living room.

Mine is the least inexpensive one, the 3A. I've already asked my better half for an even larger one to which she rolls her eyes and says "ok little boy"...
But Lortone makes good stuff.

http://www.lortone.com/tumblers.html

Its a fairly inexpensive hobby that doesnt take much of my time - maybe once a week for 15-20 minutes is all. The grit is cheap and the rocks are cheap to free :)

Now if you are really crafty, you can build your own. I saw one guy built one out of an old truck tire and he can tumble about 30lbs of stone at one time. Thats a little overboard for me.

[hewhocaves]

If you're giving away pretty rocks - I'll take one!

and if I can find time, I'd love to come help dig away! it's a long trip and gas my be $10-/ gallon by then.

[Teresa]

yes! shiney rocks! I'm in.

Teresa -- while you cannot definitively say that the coloring of a rock is from one element/cation -- can you say that it's most likely from a certain element/cation? Or maybe, from a higher concentration of element/cation than other impurities?

Well, you can say that certain colors are diagnostic, once you learn what the colors are. For example-- iron ore is gray and speckly (specular), with a bluish cast, or black, or ochre yellow, or brown looks like rust....Lead is gray. Gold is usually gold...or associated with quartz or this green and white stuff I've seen as matrix for gold ore. Copper ores are usually sea green, or bright blue, or actually look copper. Granite: usually black, white, clear, and/or pink /red. Can't say I've ever seen purple or green granite--though they may exist.

I think it would be more that there are 'typical colors'--except in the case of gemstones which are defined by their color--for example corundum by any other color is sapphire, red corundum is ruby, or amethyst--defined as purple quartz.

Colors can fool you though. Being a mean TA, I would give kids green fluorite and basalt with big pink phenocrysts for their tests. Not enough of those zingers to fail a student, of course, but one or two to humble the know-it-alls..

Now, if you ID a rock by a suite of characteristics--color+texture+hardness+any other weird characteristic you are much safer.

[Evan G]

I've ever seen purple or green granite

We have tons of it, it is call Serpentine Granite. Purple granite exists too but forgotten the name of it. I have seen in patches here in the Tetons and also in the Brechenridge, CO area.

iron ore is gray and speckly (specular)

Can iron ore in trace amounts be red or blood red, like in red tigereye?

[hewhocaves]

Can't say I've ever seen purple or green granite--though they may exist.

green granite is apparantly possible - there's a place in Australia where oxidizing iron has lent granite a green color as well as a place in Ontario and possibly South Dakota and the Baltic. A picture of the Baltic granite can be found here:
http://www.graniteland.com/stone/baltic-green.html
its apparantly more of a syenite.

as for purple granite...
http://www.johnsongranite.com/PA.htm
it took a bit longer to find. Though that may be more of a migmatite.

There's some chineese granites that can look purple. The General Red and the Qilu Red are supposed to fall into those categories.
Anyway, there's a fairly interesting list here:
http://www.findstone.com/daniel2.htm

Colors can fool you though. Being a mean TA, I would give kids green fluorite and basalt with big pink phenocrysts for their tests. Not enough of those zingers to fail a student, of course, but one or two to humble the know-it-alls..

my petrolofy instructor liked to throw in some stones in a cement matrix and put it with the regular things to identify. It was cosidered correct if we identified it as *concretite*. Another favorite of his was *brickite*.

Now, if you ID a rock by a suite of characteristics--color+texture+hardness+any other weird characteristic you are much safer.[/quote]

agreed. and if you have a chance, take it back home, slice it up, look at it under the microscope, yada yada yada.
It is possibly the most common misconception that there are effectively little tags on rocks which only geologists can see which conclusively tell him what the sample is with just a glance.

John