Library transfer between distinct Laser-Induced Breakdown Spectroscopy systems with shared standards

The mutual incompatibility of distinct spectroscopic systems is among the most limiting factors in Laser-Induced Breakdown Spectroscopy (LIBS). The cost related to setting up a new LIBS system is increased, as its extensive calibration is required. Solving the problem would enable inter-laboratory reference measurements and shared spectral libraries, which are fundamental for other spectroscopic techniques. In this work, we study a simplified version of this challenge where LIBS systems differ only in used spectrometers and collection optics but share all other parts of the apparatus, and collect spectra simultaneously from the same plasma plume. Extensive datasets measured as hyperspectral images of heterogeneous specimens are used to train machine learning models that can transfer spectra between systems. The transfer is realized by a pipeline that consists of a variational autoencoder (VAE) and a fully-connected artificial neural network (ANN). In the first step, we obtain a latent representation of the spectra which were measured on the Primary system (by using the VAE). In the second step, we map spectra from the Secondary system to corresponding locations in the latent space (by the ANN). Finally, Secondary system spectra are reconstructed from the latent space to the space of the Primary system. The transfer is evaluated by several figures of merit (Euclidean and cosine distances, both spatially resolved; k-means clustering of transferred spectra). The methodology is compared to several baseline approaches.Comment: 32 pages, 22 figure

Uvite, CaMg3(Al5Mg)(Si6O18)(BO3)3(OH)3(OH), a new, but long-anticipated mineral species of the tourmaline supergroup from San Piero in Campo, Elba Island, Italy

Uvite, CaMg3(Al5Mg)(Si6O18)(BO3)(3)(OH)(3)(OH), is a new mineral of the tourmaline supergroup. It occurs in the Facciatoia quarry, San Piero in Campo, Elba Island, Italy (42 degrees 45' 04.55 '' N, 10 degrees 12'50.89 '' E) at the centre of a narrow (2-3 cm wide) vein composed of aggregates of dark brown to black tourmaline, penetrating (magnesite + dolomite)-rich hydrothermally altered metaserpentinite. Crystals are euhedral and up to 1 cm in size, brown with a vitreous lustre, conchoidal fracture and grey streak. Uvite has a Mohs hardness of similar to 7 1/2, a calculated density of 3.115 g/cm(3) and is uniaxial (-). Uvite has trigonal symmetry, space group R3m, a = 15.9519(10) angstrom, c = 7.2222(5) angstrom, V = 1597.3(1) angstrom 3 and Z = 3. The crystal structure was refined to R-1 = 1.77% using 1666 unique reflections collected with MoKa X-rays. Crystal-chemical analysis resulted in the empirical crystal-chemical formula (X)(Ca(0.61)Na(0.35)A(0.04)) S1.00Y Mg1.50Fe0.472+Al0.71Fe3+similar to 0.14Ti(0.1)8 similar to S3.00 Z Al4.54Fe0.183+V3+similar to 0.02 Mg-1.27) S-6.00 T Si5.90Al0.10()similar to S6.00O18 similar to BO3() 3O(3)(OH) 3O(1)[(OH)(0.55)F0.05O0.40] S1.00which recast in its ordered form for classification purposes is:Uvite is a hydroxy-species belonging to the calcic-group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are fluor-uvite and feruvite, to which uvite is related by the substitutions W(OH)-. WF- and YMg2+. YFe2+, respectively. The occurrence of a solid-solution between uvite and magnesio-lucchesiite, according to the substitution ZMg2+ + W(OH)-. ZAl(3+) + WO2-, is supported by experimental data. The new mineral was approved by the IMA-CNMNC (IMA 2019-113). Uvite from Facciatoia formed by the reaction between B-rich fluids, released during the crystallisation process of LCT pegmatites, and the surrounding metaserpentinites, altered by contact metamorphism in the aureole of the Miocene Mt. Capanne monzogranitic pluton