Verneite, Na 2 Ca 3 Al 2 F 14 , a New Aluminum Fluoride Mineral from Icelandic and Vesuvius Fumaroles

• Published in: Minerals
• Main Authors: Tonči Balić-Žunić, Anna Garavelli, Daniela Pinto, Donatella Mitolo
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2018
• Subjects: verneite; new mineral; crystal structure; Hekla; Vesuvius; Eldfell; aluminofluoride; Mineralogy; QE351-399.2; Jules; Verne; Iceland
• Online Access: https://doi.org/10.3390/min8120553; https://doaj.org/article/7f1a173f3a014ca7b989ba44bc1f9472

Verneite, Na 2 Ca 3 Al 2 F 14 , is a new mineral first discovered in fumarolic samples from both Hekla, Iceland and Vesuvius, Italy. Additional occurrences are so far from Eldfell and Fimmvörduhals, both on Iceland. Verneite is cubic, I2 1 3 , a = 10.264(1) Å, V = 1081.4(3) Å 3 , Z = 4, and corresponds to the known synthetic compound. The empirical formula is Na 2.01 Ca 2.82 Al 2.17 F 14.02 (scanning electron microscopy with energy dispersive spectrometer from an unpolished sample). It appears in crystals up to 20 μm in diameter, with {110}, {100}, and {111} as the main forms. In the crystal structure of its synthetic analogue, Na is coordinated by 7 F atoms in the form of a capped octahedron, Ca with 8 F atoms in the form of a bisdisphenoid, and Al with 6 F atoms in the form of an octahedron. The crystal structure of Na 2 Ca 3 Al 2 F 14 contains sinuous chains of Ca coordination polyhedra interlacing with similarly sinuous chains of Na coordination polyhedra and forming together with them layers parallel to {100}. The intersecting layers parallel to three equivalent crystallographic planes form a three-dimensional mesh with Al coordinations imbedded in its holes. The characteristics of Ca coordinations in fluorides, as well as their relations to other ternary Na⁻Ca⁻Al fluorides are discussed. Verneite is named after Jules Verne.