Lucabindiite
Lucabindiite is a mineral discovered in 1998 from the La Fossa crater at Vulcano, the Aeolian Islands off the coast of Italy. It has the formula (K,NH4)As4O6(Cl,Br) and is Hexagonal. After months of collecting sublimates and encrustations, the researchers discovered Lucabindiite which was found on the surface of pyroclastic breccia. The mineral is named after Luca Bindi, who was a professor of mineralogy and former head of the Division of Mineralogy of the Natural History Museum of the University of Florence.
| Lucabindiite | |
|---|---|
| General | |
| Category | Arsenic minerals |
| Formula (repeating unit) | (K,NH4)As4O6(Cl,Br) |
| Crystal system | Hexagonal |
| Space group | P6/mmm |
| Unit cell | a = 5.2386(7) Å, c = 9.014(2) Å |
| Identification | |
| Color | Colorless - White |
| Cleavage | No Cleavage |
| Fracture | No Fracture |
| Tenacity | Brittle |
| Luster | Vitreous |
| Streak | White |
| Density | 3.68 g/cm3 (Calculated Measurement) |
| Ultraviolet fluorescence | Not Fluorescent |
Occurrence and physical properties
The researchers discovered a minute amount of crystals of Lucabindiite, therefore they could not perform a direct measurement of the refractive index. However, two other methods, Mandarino Method (1981) and Korotkov & Atuchin Method (2008), were used to estimate the average refractive index. These values are 1.92 and 1.88 respectively. The small amount they obtained made it difficult or impossible to measure other physical properties. The density was calculated at 3.68 g/cm3. The mineral is very brittle, shows no signs of cleavage, parting or fracture patterns, and hardness was not determined. Lucabindiite is formed by the occurrence of steam of hydrogen halogenides, and arsenic. Lucabiindite is also found in conjunction with arsenolite, K & NH4 halides, orpiment, realgar, kirkiite, and vurroite. Lucabindiite has a structure containing (001) layers of neutral As2O3 sheets. Each sheet is formed by pyramids and is connected by a shared interlayer Oxygen.
Chemical and spectroscopic studies
Lucabindiite has the formula (K,NH4)As4O6(Cl,Br). A quantitative analysis was performed using an ED spectrometer due to the small sample size of 100 µm smeared on a 30nm thick film of carbon. The chemical formula obtained from this method is [(K0.51(NH4)0.49]Σ1.00As4.00O5.93(Cl0.48Br0.40F0.19)Σ1.07 on the basis of 7 anions. The presence of ammonium was confirmed using the structure refinement and FTIR (Fourier-transform Infrared) Spectroscopy. X-ray powder diffraction (XRD) was performed on Lucabindiite and the values calculated are: a = 5.2372(2)Å, c = 9.0085(7)Å, V = 213.98(2)Å3.
References
- Garavelli, A., Mitolo, D., Pinto, D., Vurro, F. (2013): Lucabindiite, (K,NH4)As4O6(Cl,Br), a new fumarole mineral from the "La Fossa" crater at Vulcano, Aeolian Islands, Italy. American Mineralogist, 98, 470–477.
- Mandarino, J.A. (1981) The Gladstone-Dale relationship. IV. The compatibility index and its application. Canadian Mineralogist, 19, 441–450.
- Korotkov, A.S. and Atuchin, V.V. (2008) Prediction of refractive index of inorganic compounds by chemical formula. Optics Communications, 281, 2132–2138.