End-member villyaellenite from Mapimi, Durango, Mexico; descriptive mineralogy, crystal structure, and implications for the ordering of Mn and Ca in type villyaellenite

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Authors:Kampf, Anthony R.; Ross, Charles R., II
Author Affiliations:Primary:
Nat. Hist. Mus. Los Ang. Cty., Los Angeles, CA, United States
Univ. Calif., United States
Volume Title:American Mineralogist
Source:American Mineralogist, 73(9-10), p.1172-1178. Publisher: Mineralogical Society of America, Washington, DC, United States. ISSN: 0003-004X
Publication Date:1988
Note:In English. 12 refs.; illus. incl. 7 tables
Summary:The second occurrence of villyaellenite, at the Ojuela mine, Mapimi, Durango, Mexico, has yielded the nearly pure end-member of the species, close to pure Mn5(H2O)4(AsO3OH)2(AsO4)2. The mineral occurs as a compact spray of orange-pink prismatic crystals < or equal to 4 cm in length, associated with ogdensburgite, arseniosiderite, adamite and chalcophanite. Crystals are elongate parallel to [001] with forms 100, 110 and 101. There is a good 100 cleavage; H approx 4. Optically it has alpha 1.713(2), beta 1.723(2), gamma 1.729(2); 2Valpha 70(5) degrees ; pleochroism: alpha very pale orange-pink, beta exceedingly pale pink-orange, gamma pale orange-pink. The sp. gr. is 3.69, with D(calc.) 3.72 g/cm3. Single-crystal X-ray precession data indicate space groups Cc or C2/c; the latter is confirmed by structure analysis. Cell parameters are: a 18.015(5), b 9.261(2), c 9.770(3) Angstrom; beta 96.238(7) degrees . The strongest powder XRD lines are 8.21(100), 3.243(80), 3.209(70), 3.068(70), 1.678(60) Angstrom. The refractive indices, specific gravity, chemistry and cell parameters differ markedly from those of type villyaellenite from Sainte-Marie aux Mines, France, which is near the midpoint of the villyaellenite-sainfeldite series. A third occurrence of villyaellenite at Sterling Hill, New Jersey, consists of material nearly identical chemically to the villyaellenite from Mapimi. Villyaellenite is isostructural with sainfeldite and hureaulite. The crystal structure of the near end-member from Mapimi has been refined by the method of least squares on the basis of 1183 reflections measured on an automated single-crystal diffractometer to R = 0.076 (Rw = 0.089). [J.A.Z.]
Subjects:Alkaline earth metals; Arsenates; Calcium; Crystal chemistry; Crystal structure; Electron probe data; Geochemistry; Manganese; Metals; Mineral data; Mineralogy; Minerals; Optical properties; Order-disorder; Physical properties; Durango Mexico; Mapimi Mexico; Mexico; Ojuela Mine; Villyaellenite
Abstract Numbers:89M/2270
Record ID:1988079902
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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