Crystal structure and comparative crystal chemistry of romanorlovite

Zubkova N. V., Krivovichev S. V., Pekov J. V., ZolotarevA. A,, jr., Pushcharovsky D. Yu., Sidorov E. G.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 4. P. 92-102

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Language: Russian

Abstract

Crystal structure and crystal chemical features of a new, discovered in fumaroles of the Tolbachik volcano (Kamchatka) copper and potassium hydroxychloride—romanorlovite, with the simplified formula K₁₁Cu₉Cl₂₅(OH)₄ · 2H₂O (Z = 4), are reported. The mineral is tetragonal, I4/mmm, a = 17.5538(19), c = 15.8620(17) Å, V = 4887.7(9) ų. The structure was determined using single-crystal XRD data and refined to R = 5.49 % for 769 unique reflections with I > 2(I). The structure is based on two main blocks built by Cu²⁺-centere polyhedra. The first one includes chains consisting of edge-sharing CuCl₄(OH)₂ octahedra. In the chain a fragment built by four edge-sharing Cu(1)-centered octahedral could be distinguished whereas Cu(2)-centered octahedra are connected with this fragment from both upper and lower sides. The second structural block consists of isolated Cu₆Cl₁₈ clusters built by Cu(3)-centered tetragonal pyramids and Cu(4)-centered distorted tetrahedra. In a core of the cluster Cu²⁺ and Pb²⁺ cations statistically replacing each other in the same site are located. Two these basic structural blocks are connected via distorted ACl₆ octahedra (A = Cu, K) forming pseudo-framework. K⁺ cations are located in the voids and channels of the pseudo-framework. Romanorlovite has the crystal-chemical formula K₂₄(K,Pb)₁₆(K,Cu,□)₈Cu₂₈(□,Cu)₁₆(□,Cu,Pb)₂Cl₉₂(Cl,□)₈(□,Cl)₈ · (OH)₁₆ · 8H₂O (Z = 1). Various defects revealed in its structure are discussed.

Key words: romanorlovite, new mineral, copper hydroxychloride, crystal structure, structure defect, fumarole, Tolbachik volcano, Kamchatka.