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Does anyone have additional information on the disruptive formation of "tubes" in agate nodules?

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asked Dec 5, 2015 by arbayowling (180 points)

1 Answer

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Karen Bzrys wrote a book. She is the agate lady. Her website is agatelady.com. I pretty much paraphrased her in an earlier post about tube agates and what forms them.
answered Dec 7, 2015 by Weasel (38,360 points)
Hi Weasel, I read the following from her website:

"Tube Agate: During the formation of some agates, parallel projections of tiny hair-thin mineral rods grow first within the silica gel, around which later the chalcedony agate micro-crystals form. In some cases the inclusions remain, but sometimes they weather away leaving hollow tubes that subsequently fill in with silica.”

What is being said does not explain why the tubes are invading the agate nodule and disrupting the banding process as shown in my second picture. From my perspective the tubes are an exterior organic phenomenon as evidenced by the  tubes on the surface of the nodule skin burrowing into the nodule.

Take a look at my second picture and see the burrowed holes, they are top down and not coming from within.

I have a lot more research to do.

Thanks  for your help.

 Cheers, Arbayowling
If you read it there are two theories of agate Genesis. One having to do with silica fluid and one with silica gel. Both involve the silica infiltrating the molten lava vesicles caused by air. Due to different pressures and temperatures sometimes it forms Quartz, chalcedony chert, agate what have you oftentimes the whole gamut in the same lava flow. In one theory, the gel forms those tubes as described. I re-read the second part last night. It is not a simple answer. I recommend her book, Agates, Inside Out. People who dedicated their whole lives to this problem cannot give you the answers you seek, definitively. These are the best theoretical answers. Good luck. The tubes in either theory are means by which silica enters the vesicles. As each successive evaporation some minerals are left behind. These minerals are so small they form micro crystals of SiO2. The crystal formation can only be seen with certain high powered microscopes, anyhow the theory states the tubes can be formed by the silica itself or be caused by other minerals which are later replaced by silica. I really had a little difficulty until I read about the petrified wood and how the fibers from the wood allowed silica in, the fibers decayed  and the silica replaced the fibers. In the explanation, she explains why some petrified wood is considered agatized and some is not.
Hello Again Weasel, thank you for your extensive reply. I too have read what has been described whereby the gel in the vesicle ferments  crystal growth being a natural outcome of the evaporation process and shrinkage of the gel. The crystal growth expands to fill either all or part of the remaining void. Also, there have been tubes formed in the gel and they grow outward towards the exterior  of the agate nodules. There are several examples of this process under Tube Agate on Google. I am ok with this process, but in my agate nodule the “hole or tube“ growth is downward into the nodule and spread. Up close it looks like some form of burrowing process took place and the passages are connected. Also, several of the potential holes have been or are covered with a yellow brown substance and by a top layer of white calcite indicating an exterior activity took place.

If you can, Google Agates of Scotland, there is an extremely interesting discussion on the formation of agates, part of which would explain my hypothesis of exterior organisms causing the "holes/tubes”.

Cheers, Arbayowling
 


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