Scenic Agate

[MJO]

Date: 12/7/2005 4:41:31 PM
Author: valeria101

Date: 12/7/2005 4:34:55 PM
Author: MJO

Hi Ana,

I emailed Michael at Gemline. He told me he had matching sets.

That was fast! Thanks

He returns my emails quickly .

 

[Richard M.]

Date: 12/7/2005 3:20:49 PM
Author: valeria101


I am not sure these are ''cracks'' - things can infiltrate chalcedony anyhow (re. the artificially induced dendrites) and I do not know if there is a definitive story of how these things form ( formed alongside with the agate, after ... )


There are different staining minerals in these dendrites, hence the different colors. I would think the background has something to do with it too.

Thanks for your links, Ana. I''m familiar with Fischer''s work but hadn''t previously seen the explanation given on Ganoksin. I''d appreciate a specific reference to Liddicoat''s 1960s writing if you have it. I know the agate experts in Idar-Oberstein, Germany, have also been able to create dendrites but don''t know how or when.

As with many unknown things concerning the quartz family of gems the exact formation methods of dendrites and other phenomena like plumes, sagenite, moss, fortifications, orbs, thundereggs, etc. aren''t all fully understood. For that matter the methods of how these minerals themselves form isn''t fully explained either nor is formation method of opal, a close quartz relative.

I''m certain some dendrites originate from cracks in these materials -- I have proof in the form of Montana agates that haven''t resealed and show the cracks where the manganese entered. Others show open or semi-healed cracks with black/brown managanese penetrating.

But I''ve always thought something else was happening as well and Fisher''s theory of electrochemical displacement with copper and tin chloride is very interesting. Still, he hasn''t demonstrated the same results with iron and manganese, the two dendritic materials most often found in nature.

There are those who believe agates and other non-crystalline quartzes may form from a soft ''silica jell'' that undergoes some process to harden it and turn it into its ultimate form. It seems possible to me that dendrites could form at that stage from the many metallic salts available in volcanic hydrothermal solutions. There are lots of interesting theories but there''s little research funding available for work on such low-cost gemstones. I''m attaching an image of a Montana agate that shows a dendritic formation developing along an existing fracture line. As you suggest, it seems to be ''growing'' into solid agate. Lots of ''unsolved mysteries.''

Richard M.

 

[pricescope]

In case cracks are involved in the process there must be capillary theory taken in consideration first and then dendrite growth.Capillary are the whole different science, like it was not complicated enough. But their involvement may explain different colors of infiltrates.



From http://www.harmons.net/cabs.html

one is quite convincing if rotated 90 degree

 

[strmrdr]

iv been following this thread.
Those things are way kewl.
guess i gota add another item to my someday list. yummy!

 

[MJO]

Date: 12/7/2005 7:51:14 PM
Author: strmrdr
iv been following this thread.
Those things are way kewl.
guess i gota add another item to my someday list. yummy!

Never add anything to your someday list. I always add them to my soon list . Especially if they are inexpensive. Just look for one you like and buy it otherwise you never get around to it. Life is way to short for that. Just be informed on what you are buying and don''t pay too much.

Regards,
Maurice

 

[Richard M.]

Date: 12/7/2005 6:07:20 PM
Author: Pricescope
In case cracks are involved in the process there must be capillary theory taken in consideration first and then dendrite growth.Capillary are the whole different science, like it was not complicated enough. But their involvement may explain different colors of infiltrates.

The process is very much beyond me: I just stand back in wonder and appreciate the fascinating beauties of nature.

I''ve begun to carve this Montana slab, which has patterns very similar to the Harmon''s images you posted. Carving''s the only way I''ll be able to cut it because there are fractures that must be eliminated that lead to most of these magnificent plume patterns. What''s hard to understand is that there are other fractures with no manganese.

Of course these agates were presumably formed as a result of hydrothermal activity from one of the three Yellowstone Caldera eruptions during the past 2 million years. Since then they''ve eroded from their host rock formations and have been rolled and tumbled down the Yellowstone river, sometimes for hundreds of miles. New fracturing probably occurred long after they were formed and were well away from the manganese source, or the process that may have caused it to precipitate out of the agate itself, similar to Fischer''s copper nitrate infusion.

 

[Richard M.]

Hi All,

There are many fascinating and colorful inclusions in agate that elicit a ''sense of wonder'' in me. This is the material that sent me off on a knuckle-bloodying mining quest to central Oregon when I was very young. Priday Plume (now Woodward Ranch) is probably the most famous plume agate of them all, although there are many plume varieties that are magnificent: Carey, Woodward, Wingate Pass, Marfa, Canadian River and dozens of others. I saw some wonderful material recently from Khazakstan, and much more is probably as yet undiscovered. This image only hints at the wonders of this kind of agate which often displays plumes of green, pink, red, and many intermediate hues.

The observant may notice that plumes form in many of the same shapes as the feathery dendrites in Indian and Brazilian agates and materials from several other locations. I suspect the same process of formation is at work in both although I have no precise idea of what it is.

After decades of studying all kinds of gems and having passing dalliances with all of them, my heart of hearts remains with my first and most mysterious and fascinating love, the quartz family. Many of these gems are far rarer than rubies, emeralds, sapphires or the other fabled stones of romantic history. Their beauty is unequalled but is largely unappreciated.

Thanks, Ana, for introducing this topic. It shows you have a wide ranging appreciation for the beauties of nature and aren''t limited by ''conventional wisdom'' about gem classifications.

 

[Richard M.]

Here''s another plume variety from Death Valley, CA -- one of many different kinds from around the world -- that illustrates another of the many inclusion forms possible in fine agates.

Richard M.

 

[glitterata]

Wow, those are just astonishing! Thanks for showing us.

 

[Richard M.]

Date: 12/9/2005 5:08:16 PM
Author: glitterata
Wow, those are just astonishing! Thanks for showing us.

That was just a taste. For a feast go HERE

 

[valeria101]

Date: 12/9/2005 6:09:54 PM
Author: Richard M.


That was just a taste. For a feast go HERE

Wow!

.... and sure enough, the Indian agates have a cousin, in Colorado apparently:

PS. thank you for the nice words in a previous post up here, but they are not quite deserved. I met dendritic agate in very lofty company (e.g link). It is odd to think something so striking is not precious in every way.

 

[Richard M.]

Date: 12/9/2005 6:39:28 PM
Author: valeria101
It is odd to think something so striking is not precious in every way.

Apparently Queen Alexandra found it both striking and precious.

 

[MJO]

Date: 12/7/2005 3:20:49 PM
Author: valeria101


Yeah... silly side effects of talking about an auction before it ends!

Oh well...



I am not sure these are ''cracks'' - things can infiltrate chalcedony anyhow (re. the artificially induced dendrites) and I do not know if there is a definitive story of how these things form ( formed alongside with the agate, after ... )

There are different staining minerals in these dendrites, hence the different colors. I would think the background has something to do with it too.

Hi Ana,

I was getting these stones for about $10 each a few weeks ago. Now that you have everyone looking for them they''re getting alot more expensive. I''ve been outbid on a few already. Even the round one in the middle of your post that was in Gemline''s Ebay store sold. Please post pictures after the auctions are over Just Kidding.

BTW, do you know anything about Ethiopian Opal. I saw a picture of faceted crystal opal that looked beautiful but was very expensive.


Regards,
Maurice

 

[valeria101]

Date: 12/10/2005 3:12:30 PM
Author: MJO


BTW, do you know anything about Ethiopian Opal. I saw a picture of faceted crystal opal that looked beautiful but was very expensive.

Oh, the agates are still cheap (30-ish?).... a few years before this, I tried to find a larger one for display and there was nothing below 1k around! The ones at Gemline are not quite that, but I would think at some point they could cut larger if the crazy club of agate fanciers takes note

Ethiopian Opa.l.. no, not much. The name brings to mind some some better stones showing convincing fire on colorless or brownish translucent base, somewhat like the Mexican opal when it plays. I do not know anyone who specializes in high quality Ethiopian opal and the good ones may just get a bad name from staying too close to the wirewrap. Maybe I just lost touch with these.


Edited to add:
The latest report I remember of was in the AFG mag, 2003 - describing both the mining area and some exceptional pieces.