viernes, 30 de abril de 2021

Zeolitas del volcán de la Crosa de Sant Dalmai (Girona, Catalunya)

El volcán de la Crosa, también conocido como la Crosa de Sant Dalmai, comparte su extensión entre el municipio selvatano de Vilobí d'Onyar (en tierras de Sant Dalmai) y los municipios de Bescanó y Aiguaviva, en el Gironès.

Figura 1. Localización geográfica.
Localización geográfica.

Se trata de un maar o cráter volcánico ancho (de más de 1200 m, uno de los más grandes de Europa) y de baja altitud (156 msnm) formado por una erupción freatomagmática, producida por una explosión causada por las aguas subterráneas en contacto con una bolsa de magma ascendente. Las violentas explosiones han creado un anillo de proyecciones piroclásticas, formadas tanto por materiales juveniles (de composición basáltica, gredas y algunas bombas volcánicas) como por fragmentos de rocas del subsuelo (fragmentos ígneos y metamórficos). El origen freatomagmático de la Crosa lo diferencia del resto de volcanes de la zona, en los que predominan las erupciones de tipo estromboliano. Cabe decir que dentro de este volcán freatomagmático encontramos un cono más pequeño de tipo estromboliano.
El periodo eruptivo de la Crosa se encuentra entre los 7.9 y 1.7 millones de años (Ma), característico de los procesos volcánicos de la depresión de la Selva. Los de la zona del Empordà, más antiguos, datan de 12 a 8 Ma y los más recientes, los de la Garrotxa, de entre 500.000 y 10.000 años.

Imágen de Google Earth donde se observa el anillo volcánico principal y el cono secundario.















Vista del volcán de la Crosa de Sant Dalmai, desde el mirador de Can Guilloteres. 

 


 

 

 





Este volcán ha sido muy bien estudiado (Bolós et al., 2012; Pedrazzi et al., 2014). Los autores indican un proceso eruptivo en seis fases:

I. Estadio inicial. La depresión de la Selva presenta varias fallas alineadas NW-SE, con varios acuíferos.

I. Estadio inicial.









 



II. Fase freatomagmática-1. El magma ascendente aprovecha las fallas para ascender y contacta con las aguas de un nivel freático superficial. El calentamiento repentino y la vaporización del agua genera violentas explosiones, que abren un cráter de tipo maar freatomagmático. Rocas del subsuelo, gredas, bombas volcánicas y oleadas piroclásticas muy calientes arrasan la zona.

II. Fase freatomagmàtica-1.
 

 

 

 

 

 

 

 

 

 

 

 

III. Fase estromboliana-1. Cuando el agua superficial ha sido vaporizada totalmente se da un periodo de vulcanismo magmático, menos violento, con conos de gredas de tipo estromboliano.

III. Fase estromboliana-1.

IV. Fase freatomagmática-2. La bajada de presión del magma permite que el agua de acuíferos profundos penetre y se dé una serie de violentas explosiones freatomagmáticas que destruyen el cono de gredas estromboliano.

IV. Fase freatomagmàtica-2.


 

 

 

 

 

 

 

 

 

 

 

 

V. Fase estromboliana-2. Otra vez, al desaparecer el agua del medio, el vulcanismo vuelve a ser magmático y edifica el cono de escorias estromboliano que actualmente podemos ver dentro del anillo del maar actual.

V. Fase estromboliana-2.


 

 

 

 

 

 

 

 

 

 

VI. Fase efusiva final. La caldera se llena con coladas de lava y rellena el interior del anillo del maar, rompiendo parte del cráter estromboliano pequeño.

VI. Fase efusiva final.

 

 

 

 

 

 

 

 

 

 

 

Pasada la etapa eruptiva, el volcán se fue llenando de agua y se creó un gran lago y humedales. A finales del s. XVIII y principios del s. XIX se construyó una galería de unos 800 m por el drenaje de las aguas interiores (hoy en día todavía visitable) para poder aprovechar para el cultivo las ricas tierras volcánicas.

La caldera se llena de agua.


 

 

 

 

 

 

 

 

 

 

Actualmente se cultivan cereales, forraje y árboles de frutos secos como el avellano. El anillo del maar se encuentra poblado por frondosos bosques de encinas y robles, con replantaciones de pinares y eucaliptos.

También se han realizado extracciones mineras relacionadas con las gredas, como la de Can Guilloteres (donde actualmente hay un aparcamiento, mirador y paneles explicativos) o la de Can Costa.

Antiguas extracciones de materiales
volcánicos de Can Guilloteres.


 
Niveles piroclásticos
de Can Guilloteres


Gredera de Can Costa

Niveles de piroclastos y cenizas de Can Costa
 

En los márgenes de un campo de cultivo, junto a Can Costa, recogimos unos fragmentos de materiales escoriáceos con numerosas vacuolas. Estos materiales negros y porosos llevan incluidos fragmentos líticos como: feldespatos, cuarzo, granito, gneis, esquistos, olivino y vidrios volcánicos.

Material volcánico con un fragmento tipo gneis. 

Fragmento de escoria volcánica basáltica.



 

 

 

 

 

Escoria volcànica basáltica con olivino, fragmentos
de cuarzo, tipo esquisto y feldespatos.

 

 

 

 

 

 

 

 

 



En alguno de ellos observamos, dentro de las vacuolas, la presencia de pequeños agregados globulares de cristales incoloros a blanquecinos, entre transparentes y opalinos, muy brillantes.

Vacuolas mineralizadas.


 

 

 

 

 

 

 

 

Agregados opalinos de cristales prismáticos
y agregados transparentes de cristales lenticulares. FOV: 1.5 mm.

Las imágenes de microscopio electrónico de barrido mostraron dos tipos de agregados cristalinos en los cristales brillantes: unos formados por prismas alargados maclados en "cruz" y otros formados por cristales de aspecto lenticular, también maclados.

Imagen SEM donde observamos dos tipologías
de zeolitas: prismática y lenticular.

Esta macla en "cruz" se conoce como macla de Bowling.
Se trata de un tipo de macla poco habitual de la
phillipsita y el harmotoma. Muestra RM3154.

Cristales prismáticos y lenticulares.
Análisis RM3154 (prismas), RM3153 (lent.).

Cristales de aspecto lenticular (RM3153).



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

También observamos agregados esféricos
de color blanco y con estructura interna radial (RM3131).

 



 

 

 

 

 

 

 

Imagen SEM de los agregados esféricos (RM3131).

 

 

 

 

 

 

 

 

 

 

 

 


















Los primeros estudios de caracterización se llevaron a cabo por espectroscopia SEM-EDS.
El análisis elemental de las tres tipologías de agregados nos mostró que tenían una composición muy similar. En todos ellos predomina ligeramente el potasio sobre el calcio.

Tabla 1. Composición elemental.

 

Estas composiciones son muy comunes en las zeolitas. Con estos resultados, ya pudimos confirmar, por su hábito cristalino, la phillipsita-K en el caso de los cristales prismáticos maclados en "cruz" o macla de Bowling (RM3154). Sin embargo, lo confirmamos mediante espectroscopía Raman.

Espectro Raman de los prismas maclados en “cruz” (Macla de Bowling)
comparados con patrones de RRUFF. (RM3154).

 

En el caso de los agregados globulares (RM3131) obtuvimos un espectro coherente con la phillipsita. Se registró tanto la zona de baja frecuencia como la de alta donde encontramos los modos vibracionales de las moléculas de agua.


Espectros Raman de baja y alta frecuencia de los agregados globulares esféricos (RM3131).

En cuanto a los cristales lenticulares (RM3153), el espectro Raman obtenido es muy parecido al de la phillipsita pero con la desaparición de una banda a 420 cm-1 y el desdoblamiento múltiple de la banda de la phillipsita que se encuentra a 475 cm-1, en bandas a 460 y 477 cm-1 y la aparición de una débil banda a 332 cm-1. Estos resultados son coherentes con la chabazita, en este caso, chabazita-K.

Espectro Raman de la chabazita-K (RM3153) comparada con un patrón RRUFF.

Agregados incoloros de cristales tabulares de chabazita-K (RM3153),
junto con agregados globulares más blancos de phillipsita-K (RM3154).



Phillipsita-K en agregados divergentes FOV 1.3 mm.

Algunas muestras aún se encuentran en proceso de estudio y puede que se encuentren otras zeolitas o minerales característicos de estas escorias volcánicas.

El lugar merece una visita para disfrutar de la belleza de esta formación geológica y de los verdes paisajes de la zona.

 

AGRADECIMIENTOS
Al Dr. Joan Martínez Bofill, gerente de GEOMAR Enginyeria del Terreny, a Joana Lluch y Enrique Rossell, técnicos del equipo, por su amable acogida y facilitarnos el estudio de diferentes ejemplares mediante SEM-EDS. Al Dr. Tariq Jawhari, del servicio de espectroscopia Raman, de los Centres Científics i Tecnològics de la Universitat de Barcelona (CCiTUB). Al Dr. Joan Carlos Melgarejo, por su apoyo continuado en la determinación de minerales de nuestro país.

BIBLIOGRAFÍA

Pedrazzi, D., Bolós, X., Martí, J. (2014): “Phreatomagmatic volcanism in complex hydrogeological environments: La Crosa de Sant Dalmai maar (Catalan Volcanic Zone, NE Spain)”. Geosphere, vol. 10, núm. 1, pp. 170-184. https://www.researchgate.net/publication/259821063 [online, abril 2021].

Bolós, X., Barde-Cabusson, S., Pedrazzi, D., Martí, J., Casas, A., Himi, M., Lovera, R. (2012): “Investigation of the inner structure of La Crosa de Sant Dalmai maar (Catalan Volcanic Zone, Spain)”. Journal of Volcanology and Geothermal Research, vol. 247-248, pp. 37-48.

 

Ferrer, M.C., Riesco, M.: “Geòtop 356. La Crosa de Sant Dalmai”. Departament de Medi Ambient i Habitatge Direcció General del Medi Natural. Generalitat de Catalunya. https://mineratlas.com/img/4/7/3/473.pdf [online, abril 2021].

Mindat.org: Crosa de Sant Dalmai vulcano. https://www.mindat.org/loc-130949.html [online, abril 2021].



martes, 30 de marzo de 2021

RESTORATION OF THE "ANGEL's CROSS" JEWEL of SALVADOR DALÍ

Dalí was a versatile surrealist artist: a great writer, show-man, stage designer and also a painter, his best known side. Dalí works, full of allegories to his personal experiences, fears and obsessions, are exposed in the best museums worldwide. A perhaps lesser known facet is jewelry design. During his long stays in the United States he saw an important economic source fulfilling the wishes of women of the richest families and, at the same time, exploring one more field of his unattainable creativity. Dalí himself said: "When I design jewelry, as in all my art, I create what I like."


From 1941 to 1958 Dalí designed a jewelry collection and followed the entire creation process associated with Ertman and Alemany, two established jewelers and goldsmiths in New York. Dalí made the sketches that later became sculptures combining all kinds of noble materials. Throughout his life he continued to create new jewels, many of which can be enjoyed at the Gala-Salvador Dalí Theater-Museum in Figueres.

In 1958, the jewelry collection was acquired by The Owen Cheatham Foundation, a prestigious American foundation created in 1934 that ceded the jewelry collection for various charity, educational and cultural associations to raise funds with the exhibition. Finally all these jewels were deposited at the Virginia Museum of Fine Arts, in Richmond. The jewelry collection was temporarily exhibited at the Gala-Salvador Dalí Theater-Museum in Figueres during the months of August and September 1973, one year before the official inauguration of the Museum. In 1981 the collection was acquired by a Saudi billionaire and, later, by three Japanese entities, the last of them was the one that formalized the sale to the Dalí Foundation, for an amount close to 900 million of Spanish "pesetas".

Dalí’s fondness for minerals, rocks and geology, especially Cap de Creus (Girona, Catalunya), is evident in several of his works. We can also see specimens of minerals, not always the decorative classics, in his house in Portlligat. I invite you to look for them on a future visit.



The jewels on display in the Figueres museum, apart from the fascinating cutted gems (diamond, ruby, emerald, sapphire, aquamarine, topaze, etc.), are often disposed on basis of natural minerals such as quartz, opal, xylopal or beryl.

One of these wonders is the "Angel's Cross" (1960) which Dalí himself says represents "the treatise on existence: the gradual transformation from the mineral world to an angel". The sculpture, according to the artist, has been "built on the mathematics of the number 12. The same cube that immobilizes the structure of the Coral Cross is based on the number 12", as the twelve needles of the base, which they remember the movement of the spikes of a sea urchin. Twelve is symbolic in many cultures, it represents the number of perfection.

The base represents the "initial stage", the union of the mineral world represented by a base made of fragments of a quartzite rock with a layer of marcasite-pyrite and fragments of polished lapislazuli, on which we finnd the vegetal world represented by corals (sic), red as blood, and somesea urchin spikes, the animal world. This primary, irrational structure rises through the body of the cross, in the shape of a red coral, and supports a human body: Jesus Christ crucified. But this human body sublimes into a spiritual, angelic, radiating light, which can be seen perfectly when is open the huge cutted citrine gem. The whole cross structure is made up of gold cubes.


What happens to the base of the jewel?
This question is likely to be proposed by the restoration and preservation equipment of the Gala-Dalí Foundation, when in one of the routine revisions they saw that, on the base several fragments were detached.



Frontal view with the "disintegration" of the marcassite.
© Fundació Gala-Salvador Dalí.

Immediately they contacted with the reference jeweler of the Foundation, Noa Florensa. This well-known Catalan jeweler was the person who decades ago, when the Foundation is going to acquired the jewels collection, she carried out the ingent and meticulous work of restoring and giving them the splendor and the original functionalities. The years also go by the jewels. The jeweler has been intervening for years when some of the pieces show any conservation problem.

Seeing that the base was a mineral, not a cutted stone, she suggested contacting Montse Bagué and Josep Maria Serrano, two well-known gem carvers and members of the Grup Mineralògic Català, we usually find them at the mineral shows with a shop with materials and tools for stone “carvers”. They both quickly saw that it was a possible marcasite-pyrite specimen, not a sphalerite, according to a report by the Asociación Española de Gemmología that was made when the collection was purchased. Josep Maria and Montse also appreciated a treatment would be necessary which escaped from the lapidary world. For this fact they contacted me.


On my first visit, I could see it was a pyrite that had been completely or partially converted to marcasite. All mineralogists and collectors know that the marcasite in our collections can be stable for many years, but one day specimens begin to "disintegrate." A powder appears, cracks open and finally the collapse, if the cardboard or plastic box is not stained or perforated.

The "disease" of this Dalinian stone was clear: a certain degree of ambient humidity, marcasite oxidation, formation of sulphuric acid and the corresponding sulphates. A dark future was expected...

A bibliographic search of known methods in the conservation of minerals was done, focusing on the “pyrite decay” (a very Dalinian title). Several methods were put on trial, but the characteristics of the piece -with corals and lapis lazuli glued with resins-, the size of the specimen and its structure did not allow us to use certain methods.


What did we do to stop the degradation?
The method of treatment chosen, considering pros and cons, was that of ammonia vapors generated by a solution of ammonium hydroxide (NH4OH) in polyethylene glycol-400 (PEG-400) as a humectant. This process is described in several articles, but we used R. Waller’s article detailing the whole process (Waller, 1987).

The piece and fragments were mechanically cleaned. All the efflorescences, sulphates (coquimbite, melanterite, copiapite...) were eliminated. We even observed a small cavity in the matrix, between marcasite and quartzite (which was no longer of massive sulfides as we had assumed before having it "in our hands") from which dust kept coming out.

With Irene Civil and Elisenda Aragonès starting cleaning.
© Fundació Gala-Salvador Dalí.

 

Laboratory of conservation and restoration of
the
Gala-Salvador Dalí Museum, in Figueres.© Fundació Gala-Salvador Dalí.

Mechanical cleaning. © Fundació Gala-Salvador Dalí.

Mechanical cleaning. © Fundació Gala-Salvador Dalí.

Once clean, base was deposited in large tupperware with the ammonia-PEG400 mixture. PEG-400 is a very dense liquid that has humectant properties, as we said, that is, it absorbs humidity. We think that moisture is the enemy of marcasite and much more in an aggressive environment full of ammonia vapors. In this way, inbox atmosphere is kept well below the ambient during the treatment.

Ammonia vapor treatment. © Fundació Gala-Salvador Dalí.

What did we see during the treatment process?
The altered surfaces turn on a reddish-brown tone, Fe(III) hydroxides were forming. Sulphates were transformed into hydroxides. Possible sulphuric acid was neutralized to form ammonium sulphate. The healthy marcasite did not lose its color and the lapis lazuli and coral remained with their original luster.

After the treatment, the reddened surfaces were mechanically cleaned. Sample was cleaned with isopropanol and acetone to remove most of the dust from the salts formed and moisture. To protect these areas from moisture they were coated with a thin layer of Paraloid B-72, an acrylic resin widely used in repairing and protection of minerals... Some cracks were consolidated with the same Paraloid (but more concentrated) or with epoxy adhesives.


Consolidating base. © Fundació Gala-Salvador Dalí.








After this, Noa Florensa began to assemble the "puzzle" of detached fragments. A very complex puzzle: no two pieces were alike and some had disintegrated into dust, then missing pieces. The end result, after hours of testing, was quite acceptable and similar to the original.

With Noa Florensa, and the puzzle on her hands.
© Fundació Gala-Salvador Dalí.

The piece now rests in its "sarcophagus-tupperware", accompanied by desiccant silica-gel, waiting for the display case to be conditioned to maintain a permanently dry atmosphere.



 

 

 

 

 © Fundació Gala-Salvador Dalí.

 

Bacteria attack?
There has been a lot of news about the "bacterial attack" on Dalí's jewel. No, marcasite has not disintegrated due to bacteria. Humidity has been responsible. Although the Museum controls it, any occasional rise in humidity may have started the process. Bacteria, if any, are opportunistic, they have been added to the "sulphuric feast" (another very Dalinian title) to eat and defecate more acid.

The reaction-disintegration of marcasite is favored by the presence of these sulphur bacteria, such as Acidithiobacillus ferrooxidans or A. thiooxidans. However, it is also recognized that the importance of bacteria in storage conditions in dry museums is negligible if not ruled out. Fenlon and Petrera (2019) even cite a 95% HR limit, below which bacteria are not viable.

For this reason, a group of IDAEA experts in these extremophiles was also contacted, through Joan Gutiérrez (from the UB and PhD student at IDAEA), who carried out genetic studies to determine if the bacteria were there, and if any, which ones.

Recently (march 2021), we have received the information that no expected bacteria was present.





Talking about possible bacteria with Joan Gutiérrez.
© Fundació Gala-Salvador Dalí.

What is the future of the jewel base?
As we have said, marcasite is prone to alteration in the presence of moisture and oxygen, so if the piece is kept in a low humidity atmosphere we can predict many years of life to it.

However, I personally think that Mr. Dalí would have been very happy to replace the damaged base with a magnificent Peruvian pyrite, full of golden reflections (like gold!!!), like those you can find in mineral shops as balls, pyramids and obelisks or that has been used as a basis for the FIFA Ballon d'Or "Golden Ball", that a well-known Barça football player has won so many times. But Mr. Dalí is not here to opine. Therefore, it is necessary to follow the opinion of experts and preserve everything that is original, as long as possible.

And don't forget to visit the Museums that make up the constellation around Salvador Dalí. You will find more minerals than you think... 

https://www.salvador-dali.org


 


Acknowledgments
I would like to thank Montse Bagué and Josep Maria Serrano for thinking of me to do "cooking". To Noa Florensa to explain to me the point of view of fine jewelry and some techniques used. To Irene Civil, head of conservation and restoration of the Gala-Salvador Dalí Foundation, Elisenda Aragonès, conservation and restoration technician of the Foundation and Yvonne Heinert, photographer and documentalist of the Foundation, for the trust placed in me and for what they have taught me of Master Dalí. I would also like to express my gratitude to Montse Aguer, director of the Dalí Museums for her kind welcome.

Some Bibliographic notes
- Waller, R. (1987). “An experimental ammonia gas treatment method for oxidized pyritic mineral specimens”. ICOM Committee for Conservation 8th Triennial Meeting Sydney Australia 6-11 September 1987. Getty Conservation Institute.
https://www.icom-cc-publications-online.org/3203/ [March 2021].

- Tacker, R.C. (2020): “A review of “pyrite disease” for paleontologists, with potential focused interventions”. Palaeontologia Electronica. 23(3): a45. https://palaeo-electronica.org/content/pdfs/1044.pdf [March 2021].

- Fenlon, A. and Petrera, L. (2019). Pyrite oxidation: a history of treatments at the Natural History Museum, London. The Geological Curator, 11:9-18.