We use cookies to show content based on your preferences. If you continue to browse you accept their use and installation. More information. >

FMF - Friends of Minerals Forum, discussion and message board
The place to share your mineralogical experiences

FMF English Forum is moderated by John S. White and Peter Megaw
 

Spanish message board






Newest topics and users posts
27 Mar-23:05:27 Re: collection of joseph d'oliveira (Joseph D'oliveira)
27 Mar-13:51:10 Faden quartz crystals - (26) / the roger warin contribution (Jordi Fabre)
27 Mar-13:21:46 Re: collection of michael shaw (Crosstimber)
27 Mar-12:17:11 Re: collection of dontgogreen (Nunzio)
27 Mar-12:15:29 Re: collection of dontgogreen (Dontgogreen)
27 Mar-12:08:23 Re: don lum collection (Don Lum)
27 Mar-10:58:26 Re: collection of dontgogreen (Tobi)
27 Mar-08:02:42 Re: collection of dontgogreen (Dontgogreen)
27 Mar-06:29:01 Re: any idea about this (Pierre Joubert)
27 Mar-05:28:08 Re: any idea about this (Riccardo Modanesi)
27 Mar-05:13:46 Any idea about this (Marouenca)
27 Mar-04:10:56 Re: don lum collection (Carles Millan)
27 Mar-02:38:24 Re: tucson show 2017 (Pierre Joubert)
27 Mar-00:00:45 M.r. Vol 48 (2) tri-state district (Robert Seitz)
26 Mar-22:33:41 Re: a mineralogical trip through the states of usa - arizona (Robert Seitz)
26 Mar-20:27:00 The mizunaka collection - quartz with pyrite (Am Mizunaka)
26 Mar-20:09:45 Re: collection of joseph d'oliveira (Joseph D'oliveira)
26 Mar-18:49:08 Re: collection of ras (Robert Seitz)
26 Mar-16:57:31 Re: don lum collection (Don Lum)
26 Mar-16:14:40 Re: don lum collection (Carles Millan)
26 Mar-16:06:10 Re: don lum collection (Don Lum)
26 Mar-16:01:50 Re: just some collection statistics (Roger Warin)
26 Mar-15:58:29 Re: don lum collection (Don Lum)
26 Mar-15:06:15 Tucson show 2017 - some personal thoughts (Jordi Fabre)
26 Mar-11:53:02 Re: just some collection statistics (Carles Millan)

For lists of newest topics and postings click here


RSS RSS

View unanswered posts

Why and how to register

Index Index
 FAQFAQ RegisterRegister  Log inLog in
 {Forgotten your password?}Forgotten your password?  

Like
24986


The time now is Mar 27, 2017 23:25

Search for a textSearch for a text   

A general guide for using the Forum with some rules and tips
Jaspers & Agates
  
  Index -> Mineralogical Literature
Like


View previous topic :: View next topic  
Author Message

Josele




Joined: 10 Apr 2012
Posts: 270
Location: Tarifa, Cdiz


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 25, 2014 16:57    Post subject: Jaspers & Agates  

Recently I find a book which explains extensively the mechanism of jasper and agate formation, from the simplest chert or flint until the most complex agates: GENESIS AND CLASSIFICATION OF AGATES AND JASPERS: A NEW THEORY, by Marco Campos-Venuti. The author is a PhD volcanologist and editor of the Rivista Gemmologica Italiana who is a passionate collector of agates and jaspers and has written innumerable scientific papers.

The book shows a new geological model that explains the formation of most of microcrystalline and amorphous varieties of silica. The use of a geological and stratigraphic innovative approach to the theme leads to the consequence that most of the concepts are original. The most important conclusion is that silica varieties take their origin in a meteoric environment with a strong influence due to the weather and the alternation of dry and wet seasons. Host rock, pH of water, latitude and many other parameters determine the numerous varieties of silica, which are explained with the help of many photos, drawings, diagrams and tables which maintain the interest of the reading.
A must for all silica lovers.

More information:
http://www.agatesandjaspers.com/

All images Marco Campos-Venuti



agates & jaspers.jpg
 Description:
Book cover
 Viewed:  11625 Time(s)

agates & jaspers.jpg



index1.jpg
 Description:
Index 1
 Viewed:  11624 Time(s)

index1.jpg



indez2.jpg
 Description:
Index 2
 Viewed:  11633 Time(s)

indez2.jpg



jasper4.jpg
 Description:
Agates with inclusions
 Viewed:  11616 Time(s)

jasper4.jpg



agate4.jpg
 Description:
Banded agates
 Viewed:  11612 Time(s)

agate4.jpg



table4.jpg
 Description:
Agates table
 Viewed:  11607 Time(s)

table4.jpg



dia.dry-wet.jpg
 Description:
Wet / dry cycle
 Viewed:  11615 Time(s)

dia.dry-wet.jpg



_________________
Josele
Back to top
Reply to topic Reply with quote
Like
   

Mark Ost




Joined: 18 Mar 2013
Posts: 516
Location: Virginia Beach


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 25, 2014 17:49    Post subject: Re: Jaspers & Agates  

Really nice post. Look forward to following it as it progresses.
Back to top
Reply to topic Reply with quote
Like
   

Don Lum




Joined: 03 Sep 2012
Posts: 1660
Location: Arkansas


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 25, 2014 18:41    Post subject: Re: Jaspers & Agates  

Great pictures and explanation. Thanks for posting.
_________________
hogwild
Back to top
Reply to topic Reply with quote
Like
   

Rei




Joined: 09 Apr 2014
Posts: 228
Location: Hfuborgarsvi


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 25, 2014 18:52    Post subject: Re: Jaspers & Agates  

Those are some real lovlies :) Not sure what they mean by some of those terms, though. For example, what do they mean by "onyx"? Onyx is agate that's been artificially colored black, typically by carbon.
Back to top
Reply to topic Reply with quote
Like
   

Josele




Joined: 10 Apr 2012
Posts: 270
Location: Tarifa, Cdiz


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 26, 2014 05:07    Post subject: Re: Jaspers & Agates  

Rei wrote:
Those are some real lovlies :) Not sure what they mean by some of those terms, though. For example, what do they mean by "onyx"? Onyx is agate that's been artificially colored black, typically by carbon.

As occurs with many mineral varieties, the meaning of "onyx" is not something unique and precise. Etymologically the word comes from Greek ὄνυξ, which means fingernail due to his resemblance when is of fleshtone color. Sometimes onyx is applied only to black and white agates, artificially colored or not. In the book, "onyx" is used as synonym of horizontally banded agates in any color, which I think is the most general meaning.



agate4facies.jpg
 Description:
The onyx horizontal banding facies (2b) occurs when the liquid solution has no viscosity enough to override gravity. When the polimerization of the silica solution is more viscous then the other forces active in the process causes a concentric growth (2a) or a perimetric growth (2c).

image Marco Campos-Venuti
 Viewed:  11483 Time(s)

agate4facies.jpg



_________________
Josele
Back to top
Reply to topic Reply with quote
Like
   

Rei




Joined: 09 Apr 2014
Posts: 228
Location: Hfuborgarsvi


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 26, 2014 06:10    Post subject: Re: Jaspers & Agates  

Hmm, question, what does it say about the formation of the "white facies" in your picture above? Because that's something I've noticed with a number of recent specimens I've found, they form outward-in (crack-filling) in layers that match the contour of their vug, with opaque or milky, colorful chalcedony, but then they sometimes they abruptly terminate and switch to absolutely perfectly straight layers (like in your picture) of either bright white or transparent, no longer matching the exterior contours. I've been assuming that the transparent is quartz, but what is the white?

I found a really curious piece the other day which not only had one of those sort of transitions, but also had calcite in the middle. I'd wager that the calcite was from an entirely different formation event.
Back to top
Reply to topic Reply with quote
Like
   

Dale Hallmark




Joined: 16 Jun 2014
Posts: 120
Location: Texas Panhandle


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 26, 2014 06:13    Post subject: Re: Jaspers & Agates  

Josele wrote:
... In the book, "onyx" is used as synonym of horizontally banded agates in any color, which I think is the most general meaning.


That has always been my definition of Onyx as well. I have see certain calcites described as onyx too and that always confuses me.

Dale
Back to top
Reply to topic Reply with quote
Like
   

Josele




Joined: 10 Apr 2012
Posts: 270
Location: Tarifa, Cdiz


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 26, 2014 09:15    Post subject: Re: Jaspers & Agates  

Rei wrote:
Hmm, question, what does it say about the formation of the "white facies" in your picture above? ...

The horizontal white bands facies have a scarce known origin and a complex explanation. The book deals with this for the first time in literature and devotes some pages to this matter. It seems that the composition is half way between opal and chalcedony. It also can appear in form of massive layer in some jaspers.



white bands.jpg
 Description:
The white facies are always deposited horizontally, that's mainly under gravity forces into a no too viscous gel.

Image Marco Campos-Venuti
 Viewed:  11420 Time(s)

white bands.jpg



_________________
Josele
Back to top
Reply to topic Reply with quote
Like
   

Rei




Joined: 09 Apr 2014
Posts: 228
Location: Hfuborgarsvi


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 26, 2014 11:19    Post subject: Re: Jaspers & Agates  

Ah, fascinating! Thanks! :)
Back to top
Reply to topic Reply with quote
Like
   

Mike Wood




Joined: 16 Dec 2010
Posts: 455
Location: Northern England


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 26, 2014 15:08    Post subject: Re: Jaspers & Agates  

Thanks Josele for bringing this book to our attention. Agates don't normally 'float my boat' but this book by Marco Campos-Venuti looks absolutely fascinating. Plus I'm a sucker for pretty pictures; those photo's of agate slices are mind-boggling! I'm definitely going to buy a copy as soon as possible.
Cheers,
Mike

_________________
Rock basher
Back to top
Reply to topic Reply with quote
Like
   

Ed Huskinson




Joined: 15 Apr 2009
Posts: 304
Location: Kingman, Arizona


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 26, 2014 19:10    Post subject: Re: Jaspers & Agates  

Yes. regardless of style of formation, many agates display horizontal banding. And they are just that - bands that indicate the orientation of the agate in it's matrix. The phenomenon is called a "geopetal" structure, usually enabling the observer to know which way was up for the agate or nodule.

We inherited the term from paleontology, believe it or not. Early paleontologists noticed that some hollow fossils had developed horizontal deposits of mud (or whatever) in the shells. Applying the law of uniformitarionism, they realized that these late layers were formed when silt or mud (or whatever) had dribbled into the hollow spaces of brachiopods or gastropods, and had settled to the bottom, so that one could deduce the "up" direction accordingly.

I think Dr Megaw may have covered this in an earlier post. Regardless, enjoy the Agates, regardless of the nomenclature applied to them.

Ed in Kingman

_________________
La respuesta est en las rocas!! Estudiadlas!!
Ed
Back to top
Reply to topic Reply with quote
Like
   

Josele




Joined: 10 Apr 2012
Posts: 270
Location: Tarifa, Cdiz


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 27, 2014 19:00    Post subject: Re: Jaspers & Agates  

Just to comment that the current issue (July - August) of Rocks & Minerals magazine has some articles about Agates: http://www.rocksandminerals.org/index.html

I profit for posting an agate slice of my collection:



P1110176.JPG
 Description:
Agate
Unknown locality
12 x 10 x 0.3 cm

Under halogen light
 Viewed:  11221 Time(s)

P1110176.JPG



P1110178.JPG
 Description:
Agate
Unknown locality
12 x 10 x 0.3 cm

Under SW UV the macrocrystalline quartz layer and some chalcedony layers are fluorescent due to uranyl ion presence.
 Viewed:  11235 Time(s)

P1110178.JPG



_________________
Josele
Back to top
Reply to topic Reply with quote
Like
   

Jordi Fabre
Overall coordinator of the Forum



Joined: 07 Aug 2006
Posts: 3809
Location: Barcelona


Access to the FMF Gallery title=

View user's profile

Send private message

PostPosted: Jun 28, 2014 08:08    Post subject: Re: Jaspers & Agates  

Ed Huskinson wrote:
I think Dr Megaw may have covered this in an earlier post

Here it is: Endomorph or Pseudomorph? (and next posts)
Back to top
Reply to topic Reply with quote
Like
   
Display posts from previous:   
   Index -> Mineralogical Literature   All times are GMT - 5 Hours
Page 1 of 1
    

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


All pictures, text, design Forum FMF 2006-2017


Powered by FMF