The Beginner's Corner - The Agates

click on pictures to enlarge.
© Pictures : MJX, except otherwise specified.

Warning :

This study is guided by a book being used as discussion thread.
The author has commited not to plagiarize the texts. He comments however on the structure of the book which allows the beginner who he is - through the Internet search engines - to discover the world of agates and especially its secrecies. This article will not speak about jewellery nor of the techniques used in the industrial, technological and commercial processes related to agates.
As announced in the introduction of this series, the text proposed remains a discussion thread for the reader impassioned by the mineralogy and the beauty of microcosms of nature.
For objectivity reasons, we do not give any link with commercial sites. They are numerous on Internet. The reader will find very quickly URL addresses and will visit them. Thank you to communicate to us ( ) the exceptional or original sites.

Pictures : I thank Mr. Robert Desruelles for his photographs taken at the time of his visit to The Munich Show, and Mr. Marc Jauniaux as well.

G. Declercq

1. Introduction

"Agate?”  Boaf… - "it is commonplace!" , "nothing else?"
Well NO… the beginner which I am at 56 years in the mineral world invites you to stop, for an "AGATE" pause.
As popular as this name seems to mean, who can say exactly what is the agate? Who can speak about its origin, its composition, the laws governing its growth? Another question: are we in the presence of a final state of the material ?
Agate? No… THE Agates.

History of a discovery.What do I say? … of an unknown world.

(coll & photo MJX)

During the AGAB exhibition in November 2005, at which many CMPB members were present on both sides of the stalls, my attention was drawn by a new work on agates. "one more!", you would say . Particularly having never been sensitized with a mineral that I believed common, I took in hand a book (attention 650 pp that weighs…).    It was love at first sight for the extent of the work and the impact of the colours.  It didn’t take me long to decide to buy it. Back home, impatience had the top to devour eyes the few 650 pages of what I consider a crowned lucky find. This book of collection is an extraordinary compilation on what is however a jewel as old as the world. Therefore, I make a point of sharing the emotion of this reading to the real amateurs. I invite you to discover this path of the discovery together.

Reference : A simple title : AGATES of Johann Zenz – Ed. Bode, 2005 , 658 pp , 2000 photos

Quick appreciation : I don't want to do an idiotic publicity nor sterile, but this book allured by an extraordinary compilation of more than 2000 photographs inviting to the reading of Secrets of Book of the Earth : stones which the man emphasizes by his competence in the selection of material, the sawing and the polishing of the plates.    

Keywords : Unexpected forms, drawings harmonious, incomprehensible or strange, iridescent forms and colours, captivating and inviting to the dialogue of the stone which is revealed in its extraordinary nudity and of the reader beginner which is questioning himself unceasingly. A book to be put in all hands. 

2. To the people in a hurry

References     The agates briefly :

Collection Guy Oyhanart – 2001 – short presentation of the subject  - good teaching balance - 2 pages – Made remarks : Etymology – mineralogy of agate – various varieties – ores – « can one constitute a collection today ? »

There is also : http://en.wikipedia.org/wiki/Agate

3. The Agates – History

It is more than likely that the history of agates goes up at the age of the stone (Sumerians from Mesopotamia, Egyptians, Babylonians), that close to us and doubtless also elsewhere in the world. Theophrastus (376-287 BC), Greek doctor, philosopher and naturalist mentioned them in its treaty "Peri Lithon" (Stones). In his opinion, the first Greek layers would come from a river Akhates (Dirillo) in the south of Sicily. Thus since Antiquity, the agates were used for rings, jewels, vessel, products of ornamentation, etc… thanks to the richness of the varieties of colours and the originality of the forms. One allotted also a significance of symbols and religious values to them (seals, amulets, weapons, tools). Byzance, Rome continued the work and the trade of the agate stones (cabochons, rings…). Let us not forget the carnelite (Epos de Gligamesh), nor the famous  " Pebbles of Nile"..

(coll & photo MJX)

The agates have an old history. There are written documents, as follows :

- the old manuscript "Codex Vaticanus Graecus 1302" with updates in the 12th and the 14th centuries. etc…
- In 1755 were published in Paris the treatise of ORYCTOLOGIE ("Treatise on grounds, stones, metals, minerals and  fossils" 
- Mr. Collini printed in Mannheim in 1786 the "Diary of a trip which particularly contains various mineralogical observations on the AGATES and basalt  –  with  details on the manner of working Agates ".
- At the times of the 18th and 19th centuries, also appeared many German books (see the historical heading in the book of Zenz) 

At all times, the lapidary industry of agate existed, producing objects of ornament or ornamentation or even pavements. Some discoveries in the last century in South America, starting from huge layers, even resulted in making use of it as ballast for the ships having to return empty to Europe. 

Reference :  
few pages of a simple work : Encyclopaedia of minerals  –  J Kourimscky  –  1979: pp 149 to 157  Gründ Ed.

4. Industrial uses

Because of its hardness and its resistance to the chemicals, the agate material is used for the mortars of pharmacy and laboratory, as polishing stones in the trades of leather and paper, for certain scientific instruments.

5. Deposits in the world

It is clear that an inventory of the deposits in the world is quite simply impossible. The author of the book even points out exotic places such as Greenland or the Antarctic. A fortiori, to want to constitute a very complete database of images becomes a phantasm. Let us simply READ and travel on the way of the discovery, simply searching the beauty.

(coll & photo MJX)

The most known European bed of Idar-Oberstein (Germany), of Scotland, of Sicily, of Czech Rep. (Giant’s Mounts), of Saxony (Schlottwitz), of Romania, or North Africa such as Egypt are exhausted. Currently Brazil (state of Rio Grande do Sul) exploits in an intensive way the abundant mineral layers of very good quality. Elsewhere, and almost on all the continents, one finds certainly agates in abundant quantities, but of less quality (China, Mexico, Uruguay, the Indies, Australia, USA, Patagonia, Kazakhstan, Mongolia, Morocco, the Ural, Siberia, Madagascar, France (Esterel)…) - http://www.hunterian.gla.ac.uk (search Agate)

6. Translations

Reference : the beginner in mineralogy, as well as very good informed collector, knows that the use of its mother language wedges him in an extremely restricted bubble. English and German in this field are of utility impossible to circumvent. It remains that the scientists of Hispanic language are quite well present on the market as well as the Chinese. There are the Italians and the others. And what to say about the treasures in the "European Eastern countries ", rich of an extraordinary inheritance to discover.  Consequently, see absolutely: http://www.answers.com/topic/agate

Fast appreciation :  quite surprising is this site which offers you all that it is necessary to know about vocabulary, translations, pronunciations, general info:  very well.

(coll & photo MJX)

7. Agates : Mineralogy

Origin :

The basaltic lava charged with gas going up to the surface of the earth releases gas bubbles which are at the origin of almond cavities in the “melaphyre” and similar rocks. Under the supply of hydrothermal solutions, deposits are formed in rhythmic sedimentations of silica to the state of jelly, in regular layers with chemical contents and various dyes. In hollow agates, the mechanisms associated with the dissolution of silica and other minerals will allow the formation of the amethyst and quartz, rock crystals.

Properties :

Of the family of silica, the agate belongs to the group of chalcedony.
It is about a silicon oxide SiO2 , mixture of cryptocrystalline chalcedony, rhombohedric quartz and of amorphous opal. By cryptocristalline, it is necessary to hear " very small crystal assembly (some µm), not easily visible with the optical microscope because of the superposition of several crystals in the thickness of the thin blade (0,02 to 0,03 mm)"
Hardness: from 6.5 to 7 -  Density : 2.49 to 2.64 – fracture : conchoidal
Caution: at the interior of only one agate (Brazilian), the density is variable (cfr Pr.HAALE)
Porosity : varies from 0.15 to 0.45 % (reason for which one can easily tint the stone).
Dissolution easy in hydrofluoric acid.

Colours :

- In theory, at the origin of aqueous solutions, the formation of agates is always done in cavities in the center of which develop hyaline or of amethyst type crystals.
- But there is an unexpected multitude of colours:
- According to the mineral contents of the various layers, the structure is filamentous with very fine grains, granulous or compact. The mineral dyes are generally hematite, limonite, manganese, the greenish chlorite. The fine porosity of certain agates (Brazilian) will allow an artificial colouring (see below).
-  blue colour is due to the Tyndall effect, namely that the light diffuses in submicroscopic inclusions.
- During the observation, the colour can suddenly give the impression to contain brown scratches (case of light of very strong intensity)
- Another modification of the colours: their disappearance or change in the presence of certain acids (Bostwana Agates) (cfr Haake 2000)
- Reference: See surprising images of the book of Zenz p 39

Crystalline system :

One can see that it is the oxygen which ensures the bond with the silica atoms. 
Mineralogically speaking, the agate is full of mysteries: still today, in spite of  elaborated recent studies, the genesis of agates remains a source of many questions.
The first layer observed of a stone is generally a mixture of silica and moganite. The following layers are pure quartz.
Another curious thing, the agate fibres grow according to a helicoidal process; they are twisted.
Another characteristic: direction of crystallization of fibres: growth of fibres perpendicular to the normal direction of mineral.
The colours come from elements such as iron or manganese.
According to the more or less strong presence of manganese, one obtains "foams" textures.

The growth curiously resembles to matriochkas.
ARNOTH in 1986 illustrated how to saw an agate. The shape of the section will be completely different according to one or the other perpendicular used. Take an onion, cut it according to its "diameter" or to the direction of the stem.
The escape channels are very common in agates. For the specialists, they are synonymous with "Injection holes – access channels – outflow channels, diffusion of  solutions channels, evaporation tubes, eruption channels. 

RYKART, BLANKENBURG and LANDMESSER explain this phenomenon and bring to the conclusion: "Each agate is unique, none is similar with another one. Even when agates are genetically formed together, their forms, colours, characteristics are different; recutting a section of agate a few mm further, different forms can appear .Wonderful !
See bibliography Zenz p 41    

The specialists agree for saying that the geochemistry of agate is one of most complicated.
For more information, consult the site: http://www.rps.psu.edu/0109/form.html , the article of Nancy Marie Brown How agates form? interviewing Prof Peter Heaney, Ph.D.(associate professor of geosciences in the College of Earth and Mineral Sciences). 

Formation of agates

Also let us quote for information the recent work of Rykart (1989), H.R. SCWEIZER (1986), ARNOTH (1986), LANDMESSER (2001), MOXON (1996)

Colours

The strictly natural agate has concentric zones of very varied, highly contrasted and moderated colours, from colourless, white, gray, brown, red to green black.

Ancient faking : the majority of commercial agates are artificially coloured to become ONYX (dyed white with bands black or brown) or SARDONYX or sard (bands brown-red).

8. Cutting process and polishing

We will not develop these industrial techniques. For more information the interested reader has to read pages 93 to 101 of the book of Zenz, or the specialized literature.
A remark to be pinned: the lying position on the belly (with a small cushion) of the workmen polishers of the stones, in front of the  large grinding stones, generally actuated by water mills. 
The world reputation of Idar Oberstein (Germany) is not any more to make.

9. Agates and fossils - contradiction

In December 2002, the image of a spiral inside an agate was published in a specialized magazine, which caused impassioned and enthralling reactions on the occurrence or not of microfossiles within agates. In our case: the spiral was 4 mms in diameter; origin of the sample Freisener Höhe (Germany). Analyses proved that they were inorganic elements.
Question: But then, how to explain the development of this structure? 
Not so simple my dear Einstein, considering the study of Schäfer in 2002 on structures called "holospherulithes of the type I and II"). 
For more detail, contact simply Gisela Yvonne Lentz, University of Kiel which made a very beautiful article + photos (Book of  Zenz pp 88 and 89).
http://www.ruhr-uni-bochum.de/...

10. The most significant names

The  name of the stones are according to their forms, inclusions, the colours or their origin, they will carry the qualifier of polyhedric, nebulous, ruined, spangled, foam, sagenite, feather, brechiform, landscape, eyes, cornaline, etc. The striped agate of black and white is called ONYX.
Among evocative names, we find the agate "Condor of the Andes", my "Flowers of rain of Nankin", the "Thundereggs" (eggs of thunder).
Most astonishing remains a Mexican agate which represents an owl on blue bottom harms: "Apache hooded Owl". The latter was used as topic carrying for Mineralogical Show Munich.

http://www.webmineralshop.com... (voir aussi sa photo Zenz – p 413)

Among the names in relation to their structure, let us say Agates… « Eye, Banded, Picture, Dentritic, Thunderegg, Fire, Flame, Fortification,Vein,  Iris, Landscape, Liesegang Bands, Fragmented Membrane, Moss, Plume, Tube,...»

Alphabetic classification of names (non exhaustive)

References :

• The visit of the site of Pabian R. is essential: significant bank of data  –  denomination  –  localizations  –  layers (more than 3000 recordings): http://csd.unl.edu/agates... 

   
• The agates of Northern Mexico Edina  – Cross B.L. – 1996, (Burgess Publ.)
• Achate. Steinerne Wunder der Natur – Gaertner H. – 1971, (Alles+Brillant)

11. Formation of agates

We spoke about the basic mechanism in paragraph 5. But that does not stop there. Always continuing the reading of our book of reference, one can read on page 85 of the comments of Pr Terry Moxon of Cambridge. In his opinion, the enigma of genesis of agates, source out of silica, the vector of transport and deposit of this same silica towards the mechanism of crystallization always remains unanswered. On the other hand, the temperature at the time of the deposit was solved by studies on the isotopes, namely that the formations took place at a temperature < 100°C. 

Age of agates

For same Pr. Terry Moxon, "the young" studied specimen has only 38 My for Mexican basalts. As for agates of Lake Superior (HAVE), they are a little older: 1.100 My  but there is still correctly necessary it to specify about which age one speaks. A publication of Hickmann A.H. of 1983 speaks about it for Pilbara Rock (Australia). Pr Moxon T, Nelson D.R. and Zhang Mr. must make a communication in 2006 on the recrystallization of samples found in Western Australia. To be continued....

Thunderegg ??? (photo RDS)

In connection with publications 

We inform below the names of those which contributed to the study of these strange but astonishing and surprising mineral, as well as the date of a significant publication, this allowing the reader to carry out more pointed library searches, about Internet by ex.

In the table that we compiled, we can see that the recent discoveries  (2004) deserve to be followed. For our readers of Russian and Slavic languages, like our Japanese friends, Korean and Chinese and those of Hispanic language, we regret not to have been able to consult work existing in their language. We ask them
to excuse us. (if necessary to transmit the infos to the writer ()).

Eye Agate (photo RDS)	Quelle famille ? (photo RDS)

12. Artificial colouring of minerals: a significant subject

Dyeing: you want it a little more blue or redder ?

Very early the fine porosity of agates was used for their colouring. Who says porosity says factor of absorption.
Dyeing agates does not go back to yesterday: 

- 2000 years ago already, Pline described the artificial treatments to manufacture black onyx.
- A Constantinople, colouring was used to give rise to false onyxes, artificially striped of white and black.
- Dake announced into 1938 that the Portuguese adventurer of the 16è century, Duarte Barbosa reported that in the Indian city of Limodra the agates had passed to fire to accentuate the nuances of red.

How to do it ? (note… Nature demolition workshop? )

It should be known that in the agate sawyers (Idar Oberstein by ex), the process of dyeing of agates was "secret defense", even during the most difficult times. We raised for you this constraint. 

photo GLR

The process is simple:

- Workshop No 1 : Take an agate of Brazil or Uruguay, gray or blue-gray preferably

- seriously Activate the iron particles by a solid heat treatment and you obtain an intense red with a red/brown.
- These typical colours will be very appreciated of your Asian purchasers.

- Workshop No 2 :You work the old way  –  As In Constantinople : it is Byzance…  

- Soak during 3 weeks agates in honey or a syrup of sugar (yes, yes…). 
- Let act, then plunge them in concentrated sulphuric acid.
- Result, the organic matter is transformed into black carbon… in the porous parts, those not being it or less remain white.
- Use the Brazilian one preferably.
- If you want to reduce in a drastic way your working times, make boil your parts in the sulphuric acid. (… the hell is not far) 

- Workshop No 3 : Bauer (1896) advises you this: 

- "To moderate blue the more delicate and deep indigo towards a blue-sky or azure is done by steeping in yellow potash of Prussia, after which, you cook it slowly in melanterite. You obtain a Berliner blue… " 
- etc…

- Workshop No 2678 and following: 

- http://galleryvoltaire.com/agates.html
- You have there almost all the receipts and ingredients ...
- By the way, if you feel like a young chemist : take your precautions 

Note: This practice to tint agates for "booster rocket" the effects of colours are thus practical current and universal: flashy "blue", "pinks" and other unnameable "greens" are not exceptions, in opposite. Truths serious traders specify the nature of the "process" added by man. One can discuss on the validity of such practices and the credit to be given for this type of trade.

The fact is there: the products are on the stalls. I would say that of good direction, it is necessary to denounce those which cheat and put at the index those which knowingly "forget" to declare it at the time of the sale, or swear their large gods who blue surprisingly intense are natural (whereas nature made gray-brown…).

13. Gallery of Photos

For information purposes we inform some sites by way of examples among much of others:

However, nothing of such as the consultation a "beautiful book of collection". In the book which is used to us as beacon for our way of discovery, we could admire at our rate/rhythm 520 richly documented pages of extraordinary photographs, only of agate photographs classified by geographical places, Germany (thank you for Europe) cutting itself (.. .) not less than 100 pages in this beautiful cake.

• http://www.russbehnke.com/..page on Mexican agates of Russ Behnke who is not any more to present.
• http://www.cst.cmich.edu/... in the middle of the page …
• http://www.delminsociety.net/... Delaware Mineralogical Society
• http://www.rps.psu.edu/0109/agateer.html
• http://www.oregongeology.com/sub/learnmore/gems.HTM

14. Projects of cultural trip

Munich 2005 : a little late
The 28 to October 30, 2005 took place the 42ème show of "Mineral –  Gem & fossil "in Munich with the particular topic" Agate Dream ". You reassure if you missed to it stage coach, the book of Zenz left at that time.
It is true that "Hooded Owl", this owl agate was visible on the spot, but it will remain from now on to admire it in 2 dimensions. For those which intend to speak for the first time about this agate, it is about a Mexican agate, property of Mr. Brad Cross, who represents in a very astonishing way a barn owl apache on bottom blue-night.

Tsarskoye Selo
A monument in Tsarskoye Selo, the Village of the tsars with St Petersbourg.
At the time of your stay in this superb town of art, do not forget to visit the "Pavillon of Agates" of the Ekaterininski palate, built in 1780; the directors and specialists experienced in gemmology Boris Igdalow and Wladimir Mesentzev will comment on you the result of their efforts in the restoration and the safeguarding of this incredible museum devoted to agates, jasper and other "amber room".

Visit of the museum of Idar Oberstein
http://www.edelsteinmuseum.de/index.htm

Active holidays?

• If you want to spend the holidays in the agate mine of Mont Lyall to Holy-Anne-of-Monts (Qc-Canada): "the recreotouristic activity proceeds in a mine with open sky and consists of the gathering of agates and géodes by the visitors. There is an exposure of minerals comprising 250 samples, animation on the site and a shop where minerals are on sale. Also, stone sawing on place " Why not ? http://www.mont-lyall.com/index.html

• Tons and Tons of agates on the beach ??? Consultez http://www.rockhounds.com/...

• Are you interested in immersed agates? Meeting at the Lake Superior (USA) with your material of diving http://www.dnr.state.mn.us/...

15. Inventories...

• Site to be discovered of Roger Pabian, Research Geologist, Emeritus, Conservation and Survey Division University of Nebraska-Lincoln - Lincoln, Nebraska : More than 3000 references…http://csd.unl.edu/...

16. Agate – Love stone?

Agate … good for the psyché, good for the body ?17. Philatelists : to your grips

In memory of Pierre Forget (1923 +30/01/2005), draughtsman and engraver of postage stamps.
"the agate", in January 2005 was the last emitted stamp of alive sound,
one of the series of minerals of the TAAF (Southern and Antarctic French Territories).

http://stampmin.home.att.net/ select « agate »
http://www.minerauxetfossiles.com/...
http://www.minerauxetfossiles.com/...
http://www.taaf.fr/...
http://www.netarmenie.com/...
http://www.nautilusgent.be/   select Fotos - Filatelie – Kenia
http://www.geo.uw.edu.pl/...
http://www.geo.uw.edu.pl/...

18. Literature

http://www.agate-nodule.com/  Under the title « Beautiful Agates », the banner page makes to the publicity of the work "The beauty of Banded Agates" of Michael R. Carlson. Plea for the beauties of the stones, the fascination of the colours and esthetics. Beautiful photographs "World class".
http://www.agate-nodule.com/... : Presentations of 5 works of different invoices
http://www.agate-nodule.com/index.htm

If you are a salesman of your agate collection: : http://www.agatenodule.com

These links will enable you to make a small tour of the question in images:

• http://www.rockhounds.com/... : To the discovery of the « Agates From The Land of Pumas And Craters” (Patagonia Puma Agates)
• Scotland : http://www.agatesofscotland.co.uk/ et http://www.scottishagates.co.uk/ – Beautiful images you can increase)

19. Additional references

http://www.mindat.org/search.php?name=Agate

LAPIS No 9 – 1988 – Bau und Bildung der Achate pp 11 à 28
Revue CMPB – Novembre 2002

20. A little of averything

http://www.naturenw.org/rock-thundereggs.htm

http://www.mikalina.com/agates_geofacts.htm

21. To conclude

Dear reader, if you managed to read and consult all the bonds hypertexts, cheer, you carried certainly out an extraordinary excursion in the ignored world of agates. Your vision of these minerals is probably different. Perhaps a new passion was it born in research from other photographs or the search from answers to the questions which can appear?
Perhaps also did you have the audacity to take your keyboard or your feather to contact such or such university? 
For my part, the drafting of this modest extremely incomplete and provisional synthesis invited me to enormously modesty in front of a simple word "Agate" which leaves percoler some drops of the wonders and the secrecies of nature. 

At the search for new Graal? (*)And if in the final analysis, it were out of agate...
(*) Extremely widespread name in the Middle Ages from XI^e to XV^e century. It indicates commonly a cut, a vase. 

Good success in your peregrination with Mrs Nature.

10/01/2006 - G Declercq

trad & update 07/11/2007 - GLR & MJX

update 29/12/2007 - MJX

If you know other references, send them to the writer ( )who will take care with great pleasure of supplementing the basic documentation of the CMPB:

References –miscelaneous
Books published after 2004
CD – DVD
Formation of agates
Galleries of photos
Museums – exhibitions – talks, etc...