This is the second update about the topic.
I prefer leaving version # 1 in its original appearance (see my Articles).
In the Update #1, 19th Jun 2016, thanks to Electron Microprobe Analysis by John Attard, the unknown mineral was provisionally identified as violarite.
Some photos were posted with this ID on Mindat galleries with this warning:

“NOTE: its chemical composition is compatible with the one of violarite, but XRD analyses are lacking. Therefore, John Attard warns: "THE ATTRIBUTION TO VIOLARITE IS A TENTATIVE. THE HABIT PUTS IT INTO DOUBT AND BRINGS UP THE POSSIBILITY THAT IT JUST MIGHT BE A NEW SPECIES".

To complete the identification, XRPD with Gandolfi camera (University of Pisa, Cristian Biagioni) was made.
Result:
crystals of pentlandite.

Identification based on article to be published in RMI Rivista Mineralogica Italiana by Giuliano Bettini et al.

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Note that the previous Attard’s results are perfectly compatible with pentlandite too, because the pentlandite has a highly variable chemical composition.

For everything else I prefer leaving version # 1 in its original appearance:
https://www.mindat.org/article.php/2329/Unidentified+silver-metallic+needles+in+Tuscany.+Updated%3A+Violarite.
My photographs published on Mindat have been updated with the correct ID: pentlandite.