Named for Alberto Dal Negro, Professor in Mineralogy and Crystallography, University of Padova, Italy. Dalnegroite, ideally Tl4Pb2(As12Sb8) 20S34 is a new mineral from Lengenbach. It occurs as anhedral to subhedral grains up to 200 µm across, closely associated with realgar, pyrite, Sb-rich seligmanite in a gangue of dolomite. Dalnegroite is opaque with a submetallic lustre and shows a brownish-red streak. It is brittle. In reflected light, dalnegroite is highly bireflectant and weakly pleochroic, from white to a slightly greenish-grey. In cross-polarized light, it is highly anisotropic with bluish to green rotation tints and red internal reflections.
The sample containing dalnegroite was provided by Luca De Battisti, an amateur collector who collected the sample at the Lengebach quarry in the summer of 2006.
Dalnegroite, Tl5-xPb2x(As,Sb)21xS34, a new thallium sulphosalt from Lengenbach quarry, Binntal, Switzerland.
F. Nestola, A. Guastoni, L. Bindi and L. Secco.
IMA 2009. Mineralogical Magazine; December 2009; v. 73; no. 6; p. 1027-1032;
DOI: 10.1180/minmag.2009.073.6.1027
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SEM image of Dalnegroite associated with Sartorite and corroded crystals of Realgar.
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| Scale bar is indicated. |
| Published in Lapis magazine 3/2010, page 24. |
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Photo
Courtesy of Lapis Mineral Magazine. LAPIS 3/2010, p 24.
This image is copyrighted. Unauthorized reproduction prohibited. |
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