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Unidentified silver-metallic needles in Tuscany. Updated: Violarite.

Last Updated: 19th Jun 2016

By Giuliano Bettini

Introduction

The locality is: Nibbiaia, Rosignano Marittimo, Livorno Province, Tuscany, Italy.
http://www.mindat.org/loc-252520.html
Locality description:
Radiolarites & Hydrotermalites, about 800m east-south-east of Nibbiaia.
Mineral list: Anatase, Brookite, Quartz, etc.
Here some pictures.

Anatase
Brookite
Quartz
Anatase
Brookite
Quartz
Anatase
Brookite
Quartz


The silvery needles

In further research we found Millerite, and a silver metallic “unknown”.
The "unknown" is sparsely scattered on hydrotermalite matrix (silver metallic grains and silver metallic needles).
The needles were mainly found embedded in calcite veins, calcite removed with HCl. As I said, they are silver white or silvery gray in color.
Here some photo.

Small silver metallic grains, unidentified mineral.

Unidentified, FoV 3mm
Unidentified, FoV 2mm
Unidentified, FoV 3mm
Unidentified, FoV 3mm
Unidentified, FoV 2mm
Unidentified, FoV 3mm
Unidentified, FoV 3mm
Unidentified, FoV 2mm
Unidentified, FoV 3mm



Silver metallic needles.

Unidentified, FoV 1.5mm
Unidentified, FoV 1.3mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.3mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.3mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm


Unidentified, FoV 3mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 3mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 3mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm
Unidentified, FoV 1.5mm




Analysis I. Electron microprobe analysis

The mineral was provisionally identified as Violarite, EMPA performed by John Attard on two samples submitted by me in Mar 2016. Samples provided by Silvana Cosmi. Very few silvery material.
John Attard warns: "it's a tentative. THE HABIT PUTS IT INTO DOUBT AND BRINGS UP THE POSSIBILITY THAT IT JUST MIGHT BE A NEW SPECIES".

Here the two samples.


BETTIN-1
Small silver metallic needle, about 1.3 mm long.





Quantitative Results for: BETTIN-1. John Attard's evaluation:
"BETTIN-1,2: these are essentially Ni-Fe-sulfide with Ni:Fe approximately equal to 2:1; my best guess is Violarite".


BETTIN-2

Silver metallic needles, small tuft, about 1.5 mm long.





Quantitative Results for: BETTIN-2. John Attard's evaluation:
"Consistent with Violarite".

Analysis II. Confirmed: Violarite

Some more samples were analyzed by John Attard for confirmation.
Here are the results.

Pic 1
Pic 2
Pic 3
Pic 4
Pic 1
Pic 2
Pic 3
Pic 4
Pic 1
Pic 2
Pic 3
Pic 4


This second set of samples is very similar to the first set.

Conclusions

- Electron microprobe analysis confirmed that this is Violarite. But I'm not able to rule out the possibility of a new species, because of the lack of information on the Internet, and because of the specific habit.
- The striations transversals with respect to the needles seem to be a distinguishing feature of these needles. See also:
http://www.mindat.org/mesg-11-376686.html
- I have found very little on the Internet, ex. [1], [2], [3].
- No needles on the Internet, I only noticed [4].
- Very few Violarite photos.
- Noticed the presence of some Cobalt in BETTIN-2. But Violarite is I would say “highly variable”, ranging ([5], weight percent) from Fe 24% Ni 24% Co 9.7% S 42% to Fe 43% Ni 13% Co 0% S 41%.

Aknowledgements

Thanks (alphabetic order) to John Attard, Valerio Benucci and Silvana Cosmi.

Appendix I: striations

Transverse striations: a distinguishing feature of these needles.
I took on two needles, where the striations are fairly obvious.
The needle on the left is about 1 mm long.
Those on the right are about 0.4 mm long.



Here is another sample, with zoom on the striations.
Max crystal size: 0.9 mm.



Another example.
The needle on the left (lenght: about 0.6 mm) clearly shows the striations.



Appendix II: silvery crystals and silvery masses

Many silvery material appears in micro crystals. Here some crystals, xx size about 100 micron.
The photos has been processed to eliminate noise and sharpen the crystal faces.



Some loose fragments, with silvery masses and silvery crystals.

FoV 7.5 mm
FoV 4 mm
FoV 2 mm
FoV 7.5 mm
FoV 4 mm
FoV 2 mm
FoV 7.5 mm
FoV 4 mm
FoV 2 mm


Silvery crystal group, in 3 different views.

Pic nr. 1. FoV: 1.5 mm
Pic nr. 2. FoV: 1.5 mm
Pic nr. 3. FoV: 1.5 mm
Pic nr. 1. FoV: 1.5 mm
Pic nr. 2. FoV: 1.5 mm
Pic nr. 3. FoV: 1.5 mm
Pic nr. 1. FoV: 1.5 mm
Pic nr. 2. FoV: 1.5 mm
Pic nr. 3. FoV: 1.5 mm


The silvery material also occurs in thin aggregates of crystals, see photos here below.

FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm


Obviously I'm not sure if the needles, the masses and the crystals belong to the same material.
I can suppose, because nearly always the presence of one of them involves the presence of the other. But I prefer not to speculate. Just photos.

Appendix III: magnetism

I wanted to try if this material is attracted by the magnet, or not.
To test it, I used a piece of ferrite ring magnet
In fact, both, both the crystals and the needles, are attracted (see photos). The crystals in a strong manner, but I can not exclude that there is magnetite somewhere.

FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm


I tried five more needles, see photos here below. The attraction exists, but is very weak.

FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm
FoV 2 mm


These (potential) magnetic properties should be examined more carefully.

References

[1] Some needles but Polydymite.
See “Polydymrite-Violarite Series”, http://www.mindat.org/min-39045.html

[2] F. A. Bannister, M.A. Deputy Keeper, Mineral Department of the British Museum, “The crystal-stucture of violarite”. [November 7, 1940]
http://www.minersoc.org/pages/Archive-MM/Volume_26/26-172-16.pdf

[3] “Cavities in the joint fractures of the norite contain 3 mm acicular Millerite needles and cleavable, violet coloured Violarite.”
http://www.mindat.org/photo-426535.html

[4] Rare Violarite crystals: "La découverte de cristaux de VIOLARITE en Belgique. Une première en Belgique! "
http://www.cmpb.net/fr/violarite.php

[5] J. R. Craig, J.B. Higgins, "Cobalt- and lron-Rich Violarites from Virginia"
http://www.minsocam.org/ammin/AM60/AM60_35.pdf









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Comments

Kermesite?

Keith Wood
11th Mar 2016 12:08am
Thanks Keith
however the color doesn' t seem reddish or red. Definitely silver.
Hmmm.......
Thanks again
Giuliano.

Giuliano Bettini
11th Mar 2016 11:30am

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