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Catri adventures. The fluorescent opal and....

Last Updated: 3rd Mar 2017

By Giuliano Bettini

The locality is https://www.mindat.org/loc-53206.html

This is my first adventure at Elba. Or at least, one of the first adventures.
At that time (late 80's) I was enthusiastic in exploring the Elba island, in all its most popular areas to search for minerals. I knew nothing of the island.
Wanting to explore the area of Monte Capanne, unknown to me, one day I went by car to La Pila. I parked the car in the country, and then climbed up a path that allowed me to go up the mountain on foot.
Beautiful trip, and beautiful collection of minerals! Or at least: what seemed to me then a beautiful collection of minerals.
It was 1990.
After a few years I wrote a book about the minerals of Elba, "Elba and its minerals, guide to research".
In the book, enthusiastic, I described the place with these words on that, which I copy in full at the end of the article. Now I summarize.
"..a path on the ridge of the mountain starts from La Pila and continues to climb for a few kilometers, until joins at the top with a dirt road to Sant'Ilario. In mid path you reach an area with traces of old excavations. Here, the rare blue beryl, but what appears most conspicuously into the white orthoclase are big bundles of black tourmaline, irregular, sometimes long 10 cm and more.
Here and there, then, quartz, orthoclase, lepidolite in beautiful forms. Nearby, altered green rocks with opal......"


----------------------

These are words from the past. We come to today. During my work as a reorganization of my minerals, and photos, inside a cardboard box I came across a rock with the label "opal, Gorgolinato".
I can not say why but, given that at this time I am venturing in UV photography, I put it under the UV lamp... et voilà! ... A beautiful green!
Here it is.
The specimen is shown under visible and long-wave UV light. I also took pictures of detail. The field of view is 1.8 cm for one of them, while it is of 5 mm for the other (under the microscope).


Opal specimen size 65x45x30mm
FoV:1.8cm
Under the microscope, FoV5mm
Opal specimen size 65x45x30mm
FoV:1.8cm
Under the microscope, FoV5mm
Opal specimen size 65x45x30mm
FoV:1.8cm
Under the microscope, FoV5mm



What I can say is that the green fluorescence confirmed my previous opal visual identification. I also did a hardness test, to be sure not to mess with chalcedony. In fact, it is scratched by a needle tip.

----------------------

At this point I remembered that when I picked up the opal, in the same rocks I collected also a sepiolite sample.
Or rather: what to me seemed sepiolite.
I had picked up because it is a very characteristic mineral. I had come up with those in Italy are called "pipe di schiuma". So I went to look for the specimens in my old boxes.
And behold, I found it!
Specimen size: 5cm x4cm x2.5cm.
The rocks in which they were opal and sepiolite were not, of course, granite. But they were deeply altered rocks. A small area of altered rocks. Precisely the rocks, climbing, which are on the left side of the path. I would have said to be "altered green rocks" Why in the same rocks?
So I went searching on the Internet if by chance somewhere was reported the presence of opal and sepiolite, together with each other.
And, in fact, it is.
https://en.wikipedia.org/wiki/Sepiolite
“Sepiolite occurs as a secondary mineral associated with serpentine. It can occur as a precipitate in arid environments. It may be associated with dolomite and opal”.
Interesting.
This for me seemed a confirmation.

But it is not.
In fact one of the Mindat experts, namely Paolo Bosio (whom I want to thank here), visually identified this mineral as opal with magnesite. However, he suggested some easy physical and chemical tests in order to confirm the mineral identification and also informed me that during the 19th century a similar material from the San Piero - Sant’Ilario area was for a certain time named “sepiolite” (D’Achiardi, 1872-73) and variuosly interpreted by different scientists; it was definitely recognized as a mixture of magnesite and opal only at the beginning of the 1900s.

This was confirmed by experiments I made, about hardness, density and reaction with hydrochloric acid. Therefore, the specimen is a solid chunk of massive, white opal, and subordinate magnesite.

So finally, I posted it on Mindat with this ID: opal with magnesite.
Here the images.
Also compared with a meerschaum pipe (Meerschaum, German for "foam of the sea", French "écume de mer", Italian "schiuma di mare") made of true sepiolite.



----------------------

Another confirmation that I wanted was about the color green
The green fluorescence.
An artefact?
A photographic mistake?
I'm not an expert on minerals in UV light. Nor photography in UV light. To try to get accurate color I did on my Canon IXSUS 115 HS a "white calibration", following the instruction booklet. However, being inexperienced, I tried to do an empirical verification.
For comparison, I have grouped some samples of different colors, and I photographed them all together. From top left:
green, the specimen with opal;
red (and partly yellow), a fluorescent sample from Boccheggiano (Gr), the so-called “strontian aragonite” or “aragostrontianite”, a carbonate material fluorescing red under UV long wave (that is, in most cases, calcite – see http://www.mindat.org/loc-54353.html);
blue, a fluorite crystal from Maffei quarry, loc. https://www.mindat.org/loc-29185.html;
white, aragonite from Castiglioncello.
Opal specimen size 65x45x30mm.
Here the photo.



Opal, UV LW green. It seems ok.


----------------------

For sake of completeness I add images of
1 the map;
2 some aquamarine fragments I found at the mid path of the climb;
3 and I add too the full text with which I described the locality, in 1996.



The map
4.5x3x3.5cm
4.5x2x3cm
The map
4.5x3x3.5cm
4.5x2x3cm
The map
4.5x3x3.5cm
4.5x2x3cm




----------------------

Full text, ref: “L' Elba e i suoi minerali : guida alla ricerca”, Pacini Editore Pisa, 1st Edition 1996, 2nd Edition 1997. (Collana Uomonatura), translated as: “Die Insel Elba und Ihre Mineralien”, Pacini Editore.

“A lato della valle del torrente Gorgolinato un sentiero sul crinale del monte parte dai ruderi di una casa diroccata e prosegue per qualche chilometro fino a congiungersi in alto con la strada sterrata per S. Ilario.
Si può raggiungere la casa diroccata da La Pila, partendo subito prima del paese, lato Procchio, nei pressi di un ponticello.
Raggiunta la vecchia casa, il sentiero continua a salire rettilineo, tra le pietre verdi che dopo poco sono sostituite dal granito (granati nelle pietre verdi).
A metà sentiero si giunge in una zona con tracce di vecchie escavazioni. Il sentiero stesso è fortemente segnato e solcato dal dilavare delle acque piovane. È qui presente del raro berillo azzurro ma ciò che appare più vistosamente entro il bianco dell’ortoclasio sono grossi fasci di tormalina nera, irregolari, lunghi a volte 10 centimetri e più.
Qua e là, poi, quarzo, ortoclasio, lepidolite in belle forme. Nei pressi, rocce verdi con opale.
Continuando a salire e scostandosi poco ai lati del sentiero, sia sulla sinistra che sulla destra, nella macchia, si trovano altri filoni pegmatitici con escavazioni vecchie e recenti. Qui è possibile trovare di tutto oppure niente secondo i casi e la fortuna (ortoclasio, quarzo, lepidolite, quarzo con inclusioni di tormalina, tormaline nere, gialle e verdi raramente integre, berillo, albite). Bello comunque il panorama; pericolose le vipere nella stagione calda. Qua e là nella macchia si trovano vistose tracce del passaggio di cinghiali, ossia terreno raspato e come arato, per metri.

E da queste zone, qui e a S. Piero, che i famosi collezionisti del passato come Foresi trassero le loro raccolte di minerali delle pegmatiti, oggi ammirabili al Museo di Firenze e a quello di Calci”.
----------------------

I translated as best, in English, with the help of Google Translate
(note: both the text and the map have, in the book, a misleading title: “Gorgolinato”. Now I think that the right title is Catri).
“To the side of the stream Gorgolinato a path on the ridge of the mountain starts from the ruins of a ruined house and continues for a few kilometers, until joins at the top with the dirt road to Sant'Ilario.
You can reach the house in ruins from La Pila, starting just before the country, side Procchio, near a bridge.
Reached the old house, the trail continues to climb straight, among the green stones that, shortly after, are replaced by granite (garnet in the green stones).
In mid path you reach an area with traces of old excavations. The trail itself is strongly marked and plowed by the flush of old rainwaters. Here, the rare blue beryl, but what appears most conspicuously into the white orthoclase are big bundles of black tourmaline, irregular, sometimes long 10 cm and more.
Here and there, then, quartz, orthoclase, lepidolite in beautiful forms. Nearby, green rocks with opal.
Continuing up and moving away slightly at the sides of the path, either the left or the right, in the bush, there are other pegmatitic veins with old and recent excavations. Here you can find everything or nothing depending on the case and fortune (orthoclase, quartz, lepidolite, quartz with inclusions of tourmaline, tourmaline black, yellow and green rarely intact, beryl, albite). Nice anyway the view; dangerous vipers in hot weather. Here and there in the bush, considerable traces of the passage of wild boars, ie. land abraded, plowed, for meters all around.

It's from these areas, here and in S. Piero, that the famous collectors of the past as Foresi drew their collections of minerals of pegmatites, admired today in the Museum of Florence and that of Calci”.






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Comments

Here's a comment I got from one of the Mindat experts, namely Paolo Bosio:
“The white compact and sometimes slightly spongy masses that occur in the neighbourhood of San Piero and Sant'Ilario were named "sepiolite" by D'Achiardi (1872-73), who actually considered them as mixtures of magnesium carbonate and silicate (i.e. magnesite and sepiolite) connected with resin opal. The same material was previously mentioned by Studer (1841) as "siliciferous magnesite", i.e. a mixture of magnesium carbonate and silica, and later interpreted by Grattarola (1872) as a mixture of magnesite, calcite, and sepiolite. Finally, in 1903 D'Achiardi recognised the presence of magnesite and opal only.

References:
Studer B. (1841): Sur la constitution gèologique de l'île d'Elbe. Bull. Soc. Géol. France, 12, 279-308.
D'Achiardi A. (1872-73): Mineralogia della Toscana. Tipografia Nistri, Pisa, 2 vol., 678 pp.
Grattarola G. (1872): Sopra alcuni minerali dell'isola d'Elba non ancora descritti o accennati. Boll. R. Comitato geol. d'Italia, 9-10, 284-297.
D'Achiardi A. (1903): La formazione della magnesite all'isola d'Elba. Atti Soc. Toscana Sci. Nat., Memorie, 20, 86-132 .”


Giuliano Bettini
6th Jun 2017 10:52am

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