A new mineral, eldfellite, was found among fumarolic encrustations collected in 1990 on the Eldfell volcano, Heimaey Island, Iceland. Associated minerals are ralstonite, anhydrite, gypsum, bassanite, hematite, opal and tamarugite, as well as a presumably new mineral with the composition Na₃Fe(SO₄)₃. Along with opal and tamarugite, eldfellite forms soft and fragile aggregates built of thin, platy crystals of micrometre size. The mineral is yellowish-green to greenish-white, with a white streak. The calculated density is 3.062 g/cm³. Eldfellite is monoclinic, C2/m, a 8.043(4) Å, b 5.139(2) Å, c 7.115(4) Å, β 92.13(2)º, V_uc 293.9(2) ų, Z = 2 and is isostructural with yavapaiite[KF_e (SO₄)₂]. The strongest lines in the powder diffraction diagram are [d (Å), I (relative to 10)]: 3.72, 8; 3.64, 5; 3.43, 5; 2.77, 10; 2.72, 6; 2.57, 3; 2.370, 6; 1.650, 3. Theche mical analysis and theX-ray diffraction data of eldfellite correspond to those of the synthetic compound NaFe(SO₄)₂.

Lucabindiite, ideally (K,NH₄)As₄O₆(Cl,Br), is a new mineral found as a medium-temperature fumarole encrustation (T = 170 °C) at “La Fossa” crater of Vulcano, Aeolian Islands, Italy. The mineral deposited as aggregates of micrometer-sized hexagonal and platy crystals on the surface of the pyroclastic breccia in association with arsenolite, sal ammoniac, sulfur, and amorphous arsenic-rich sulfurite. The new mineral is colorless to white, transparent, non-fluorescent, has a vitreous luster and a white streak. The calculated density is 3.68 g/cm³. Lucabindiite is hexagonal, space group P6/mmm, with a = 5.2386(7) Å, c = 9.014(2) Å, V = 214.23(7) ų, and Z = 1. The eight strongest reflections in the X-ray powder-diffraction data [d in Å (I) (hkl)] are: 3.20 (100) (102), 2.62 (67) (110), 4.51 (52) (002), 4.54 (30) (100), 1.97 (28) (113), 1.49 (21) (115), 1.60 (21) (212), 2.26 (19) (112). Lucabindiite’s average chemical composition is (wt%): K₂O 5.14, As₂O₃ 84.71, Cl 3.63, Br 6.92, F 0.77, (NH₄)₂O 2.73, O=F,Cl,Br –1.84, total 102.06. The empirical chemical formula, calculated on the basis of 7 anions pfu, is [K_0.51(NH₄)_0.49]_Σ1.00 As_4.00O_5.93(Cl_0.48Br_0.40F_0.19)_Σ1.07. According to chemical analyses and X-ray data, lucabindiite is the natural analog of synthetic phases with general formula MAs₄O₆X where M = K, NH₄ and × = Cl, Br, I. The crystal structure is characterized by neutral As₂O₃ sheets arranged parallel to (001). The As atoms of two neighboring sheets point at each other and the sheets are separated by interlayer M (=K, NH₄) and × (=Cl, Br, F) atoms. The name is in honor of Luca Bindi (b. 1971), Professor of Mineralogy and former Head of the Division of Mineralogy of the Natural History Museum of the University of Florence. Both the mineral and the mineral name have been approved by the IMA-CNMNC Commission (IMA 2011-010).

Fumarolic Minerals: An Overview of Active European Volcanoes | InTechOpen, Published on: 2016-09-21. Authors: Tonči Balić-Žunić, Anna Garavelli, Sveinn Peter Jakobsson, et