Bojarite, Cu₃(N₃C₂H₂)₃(OH)Cl₂⋅6H₂O, a new mineral species with a microporous metal–organic framework from the guano deposit at Pabellón de Pica, Iquique Province, Chile

Abstract

The new triazolate mineral bojarite (IMA2020-037), Cu3(N3C2H2)3(OH)Cl2⋅6H2O, is found in a guano deposit located at the Pabellón de Pica Mountain, Iquique Province, Tarapacá Region, Chile. Associated minerals are salammoniac, halite, nitratine and belloite. Bojarite occurs as blue fine-grained porous aggregates up to 1 mm × 3 mm × 5 mm combined typically in interrupted earthy crusts. The mineral is brittle. The Mohs hardness is 2. Dcalc = 2.057 g cm–3. The IR and Raman spectra show the presence of the 1,2,4-triazolate anion and H2O molecules. Bojarite is optically isotropic and n = 1.635(2) (λ = 589 nm). The chemical composition (electron-microprobe data for Na, Mg, Fe, Cu and Cl; H, C and N contents measured by gas chromatography on products of ignition at 1200°C; wt.%) is: Na 0.22, Mg 0.74, Fe 0.99, Cu 29.73, Cl 13.62, N 20.4, C 11.6, H 3.3, O (calculated by stoichiometry) 19.93, total 100.53.The empirical formula is (Cu2.68Mg0.17Fe0.10Na0.05)Σ3(N3C2H2)2.755[(OH)][Cl2.19(H2O)3.77(OH)0.04]Σ6⋅2.3H2O. The idealised formula is Cu3(N3C2H2)3(OH)Cl2⋅6H2O. The crystal structure of bojarite was refined based on powder X-ray diffraction data, using the Rietveld method. The final agreement factors are: Rp = 0.0225, Rwp = 0.0310 and Robs = 0.0417. The new mineral is cubic, space group Fd$\bar{3}$c; a = 24.8047(5) Å, V = 15,261.6(5) Å3 and Z = 32. The strongest reflections of the powder X-ray diffraction pattern [d, Å (I,%)(hkl)] are: 8.83 (31)(220), 7.19 (100)(222), 6.23 (35)(400), 5.077 (28)(422), 4.194 (28)(531), 3.584 (23)(444), 2.865 (28)(660, 751) and 2.723 (22)(753, 842).

Raman study of several Cu‐bearing complex minerals from the guano deposit at Pabellón de Pica, Tarapaca region, Chile

“…[19] The combination of conditions is exceptional unique, leading to the formation of minerals with a highly unusual chemical composition, especially nitrogen-bearing and organometallic complexes. [18,[20][21][22][23][24][25][26] The exact forming mechanisms are not well understood, but the involvement of special microbial communities is considered. Although Pabell on de Pica was a former mine, there is no obvious anthropogenic influence on the formation of rare copper minerals.…”