Lyonsite, Cu 3 (super 2+) Fe 4 (super 3+) (VO 4 ) 6 (super 3-) , a new fumarolic sublimate from Izalco Volcano, El Salvador; descriptive mineralogy and crystal structure
1987; Mineralogical Society of America; Volume: 72; Linguagem: Inglês
ISSN
1945-3027
AutoresJohn M. Hughes, Sarah J. Starkey, MaryAnn L. Malinconico, Lawrence L. Malinconico,
Tópico(s)Inorganic Fluorides and Related Compounds
ResumoAnsrn-q.cr Lyonsite, Cu3*Fe1+(VOo)? , a new iron-copper vanadate mineral, has been discovered in the summit crater fumaroles of Izalco volcano, El Salvador. The mineral, which occurs with thenardite and a Na-Cu-Fe vanadate, formed as a sublimate product from the volcanic gases. Lyonsite occurs as euhedral, black lathlike crystals up to 230 pm in greatest dimension. Lyonsite is orthorhombic, Pmcn, a: 10.296(l), b: 17.207(2), c: 4.910(l)A. The atomic arrangement of the mineral has been determined and refined to R : 0.028, R* : 0.031. The structure is based on a pseudohexagonal close-packed oxygen array. The fundamental building block consists of six isolated VOo tetrahedra that are linked, through corner sharing, to a central octahedron that is half-occupied by Cu2+ atoms. These pinwheel building blocks are connected on four sides by FeOu octahedra and on the remaining two sides by square-planar CuOo groups. The fundamental building block is isostructural with the silicate pinwheels in dumortierite. Lyonsite is opaque and has a dark gray streak and metallic luster. Z : 2 and D*rc: 4.215 g/cm3. Lyonsite displays a good {001} cleavage. The mineral is creamy white in reflected light in air. Reflectance values measured on (010) are (\, min., max.) 481 nm, 17.5,23.1o/o;547 nm, 16.6,22.3o/o;591 nm, 14.7,20.7o/o;and644nm, 14.4, 18.80/0. The mineral is named after Dr. John B. Lyons of Dartmouth College. Milligram amounts of the phase exist and are on deposit at the NMNH, Smithsonian Institution.
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