Umbrianite, K7Na2Ca2[Al3Si10O29]F2Cl2, a new mineral species from melilitolite of the Pian di Celle volcano, Umbria, Italy

作者：Sharygin Victor V^*; Pekov Igor V; Zubkova Natalia V; Khomyakov Alexander P; Stoppa Francesco; Pushcharovsky Dmitry Yu

来源：European Journal of Mineralogy, 2013, 25(4): 655-669.

DOI：10.1127/0935-1221/2013/0025-2306

• umbrianite
• new mineral
• gunterblassite
• hillesheimite
• delhayelite
• phyllosilicate
• crystal structure
• melilitolite
• kamafugite
• Pian di Celle volcano
• Italy

The new mineral umbrianite, ideally K7Na2Ca2[Al3Si10O29]F2Cl2, was discovered as an essential groundmass mineral in melilitolite of the Pian di Celle volcano, Umbria, Italy. It forms rectangular, lamellar or lath- shaped crystals (up to 25 x 30 x 200 mu m), typically flattened on {010}, and sheaf-like aggregates (up to 200- 500 mu m across). Umbrianite is commonly associated with kalsilite, leucite, fluorophlogopite, melilite, olivine (Fo(>60)), diopside, nepheline, Ti-rich magnetite, fluorapatite, cuspidine-hiortdahlite series minerals, gotzenite, khibinskite, monticellite-kirschsteinite series minerals, westerveldite, various sulphides and peralkaline silicate glass. The empirical formula (based on Si + Al + Fe3+ = 13) of the holotype umbrianite (mean of 58 analyses) is (K6.45Na0.35(Sr,Ba)(0.01))(Sigma 6.81)(Na1.22Ca0.78)(Sigma 2.00)(Ca1.85Mg0.13Mn0.01Ti0.01)(Sigma 2.00)[(Fe0.343+Al3.06Si9.60)(Sigma 13.00)O-29.00]F2.05Cl1.91(OH)(0.04). The strongest lines of the X-ray diffraction powder pattern {d[angstrom] (I-obs)} are: 9.65(100), 6.59(97), 3.296(77), 3.118(70), 2.819(53), 2.903(52), 6.91(43). The strong bands in the Raman spectrum of umbrianite are at 525, 593, 735 and 1036 cm(-1). The mineral is orthorhombic, space group Pmmn, unit- cell parameters are: a = 7.0618(5), b = 38.420(2), c = 6.5734(4) angstrom, V = 1783.5(2) angstrom(3), Z = 2. The calculated density is 2.49 g/cm(3). The crystal structure of umbrianite has been refined from X-ray single-crystal data to R = 0.0941 for 1372 independent reflections with I > 2 sigma(I). Umbrianite is a representative of a new structure type. Its crystal structure contains the triple- layer tetrahedral blocks [Al-4(Si,Al)(2)(Si,Al,Fe)(4)Si16O58](infinity) connected to each other via the columns of edge-shared octahedra CaO5F to form a 3D quasi-framework with channels filled by Cl , K-1 (inside the tetrahedral blocks) and Na-1 (between the Ca octahedral columns). Umbrianite, gunterblassite and hillesheimite, containing topologically identical triple-layer tetrahedral blocks, form the gunterblassite group. Umbrianite is unstable under postmagmatic hydrothermal conditions and alters to Ba-rich hydrated phases.

• 出版日期2013-8