Dioskouriite, CaCu 4 Cl 6 (OH) 4 ∙4H 2 O: A New Mineral Description, Crystal Chemistry and Polytypism

• Published in: Journal of Petrology
• Main Authors: Igor V. Pekov, Natalia V. Zubkova, Andrey A. Zolotarev, Vasiliy O. Yapaskurt, Sergey V. Krivovichev, Dmitry I. Belakovskiy, Inna Lykova, Marina F. Vigasina, Anatoly V. Kasatkin, Evgeny G. Sidorov, Dmitry Yu. Pushcharovsky
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2021
• Subjects: dioskouriite; calcium copper hydroxide chloride; new mineral; crystal structure; polytype; kagomé lattice; Mineralogy; QE351-399.2; Tolbachik; Kamchatka
• Online Access: https://doi.org/10.3390/min11010090; https://doaj.org/article/ec0a98f2472a4ec2ae165aa90a1db74a

A new mineral, dioskouriite, CaCu 4 Cl 6 (OH) 4 ∙4H 2 O, represented by two polytypes, monoclinic (2 M ) and orthorhombic (2 O ), which occur together, was found in moderately hot zones of two active fumaroles, Glavnaya Tenoritovaya and Arsenatnaya, at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Dioskouriite seems to be a product of the interactions involving high-temperature sublimate minerals, fumarolic gas and atmospheric water vapor at temperatures not higher than 150 °C. It is associated with avdoninite, belloite, chlorothionite, eriochalcite, sylvite, halite, carnallite, mitscherlichite, chrysothallite, sanguite, romanorlovite, feodosiyite, mellizinkalite, flinteite, kainite, gypsum, sellaite and earlier hematite, tenorite and chalcocyanite in Glavnaya Tenoritovaya and with avdoninite and earlier hematite, tenorite, fluorophlogopite, diopside, clinoenstatite, sanidine, halite, aphthitalite-group sulfates, anhydrite, pseudobrookite, powellite and baryte in Arsenatnaya. Dioskouriite forms tabular, lamellar or flattened prismatic, typically sword-like crystals up to 0.01 mm × 0.04 mm × 0.1 mm combined in groups or crusts up to 1 × 2 mm 2 in area. The mineral is transparent, bright green with vitreous luster. It is brittle; cleavage is distinct. The Mohs hardness is ca. 3. D meas is 2.75(1) and D calc is 2.765 for dioskouriite-2 O and 2.820 g cm −3 for dioskouriite-2 M . Dioskouriite-2 O is optically biaxial (+), α = 1.695(4), β = 1.715(8), γ = 1.750(6) and 2 V meas. = 70(10)°. The Raman spectrum is reported. The chemical composition (wt%, electron microprobe data, H 2 O calculated by total difference; dioskouriite-2 O /dioskouriite-2 M ) is: K 2 O 0.03/0.21; MgO 0.08/0.47; CaO 8.99/8.60; CuO 49.24/49.06; Cl 32.53/32.66; H 2 O(calc.) 16.48/16.38; -O=Cl −7.35/−7.38; total 100/100. The empirical formulae based on 14 O + Cl apfu are: dioskouriite-2 O : Ca 1.04 (Cu 4.02 Mg 0.01 ) Σ4.03 [Cl 5.96 (OH) 3.90 O 0.14 ] Σ10 ∙4H 2 O; ...