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What are the small holes in the skin of an agate nodule that continue into the substructure?

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asked Dec 3, 2015 by arbayowling (180 points)

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Tubes form in some of these agates. Agates are thought to be formed in volcanic rock which when molten has air pockets. Later, silicate rich waters seep in through these holes, evaporating and becoming a layer of mineral. The different colors come from different minerals. They were formed 1-2 billion years ago. They may be the original seams by which the moisture seeped into the agate. The agate lady has a web site and a book on agate formation which might be helpful as it goes into greater detail.
answered Dec 5, 2015 by Weasel (33,930 points)
Thanks,  Weasel I appreciate your prompt reply. I did some additional Google research on this subject and discovered the following treatise.

"A descriptive catalog of the minerals and fossil organic remains of Scarborough and the vicinity, by T. Coultas, dated 1816”


2 Tube Agate or Tubular Agate has its name from being pierced by small straight chalcedonic or carnelian tubes arranged in a parallel or slightly diverging manner not unlike the bristles of a brush sometimes the tubes are placed without any order The cavities of the tubes are for the most part filled with jasper of a blackish or dingy brown color sometimes inclining to reddish brown and not infrequently filled with opaque milk white chalcedony In the case when the erect tubes are connected by curved horizontal ones the agate is not to be denominated tubular since this construction evidently belongs to the tubiporite The tubular formation of this agate is of stalactitic origin though many of the tubes bear great resemblance to acicular spines The basis is either a clouded white or a clouded bright yellow tolerably translucent The matter filling the tubes is frequently found in a state of decomposition.  Fascinating........makes sense in a way.

A close up of the picture I sent shows the agate structure was  invaded by these "tubes" that  totally disrupted the formation of the banding. I am guessing these 'tubes" were organic and spread. I will post another view.

You were right about the agates forming in vesicles in volcanic magma, but my research finds the age of agates, particularly in this part of the world, corresponds to the shifting of the continents that occurred about 400-650  million years ago. Apparently there was considerable volcanic activity at that time and thus began the formation of agates.

Does anyone else have additional information?

Cheers, arbayowling

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