Gatelite-(Ce), a new REE-bearing mineral from Trimouns, French Pyrenees; crystal structure and polysomatic relationships with epidote and tornebohmite-(Ce)

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doi: 10.2138/am-2003-0125
Authors:Bonazzi, Paola; Bindi, Luca; Parodi, Giancarlo
Author Affiliations:Primary:
Universita di Firenze, Dipartimento di Scienze della Terra, Firenze, Italy
Other:
Museum National d'Histoire Naturelle, France
Volume Title:American Mineralogist
Source:American Mineralogist, 88(1), p.223-228. Publisher: Mineralogical Society of America, Washington, DC, United States. ISSN: 0003-004X
Publication Date:2003
Note:In English. 16 refs.; illus., incl. 7 tables
Summary:Gatelite-(Ce), ideally (Ca1REE3)Σ = 4[Al2(Al,Mg) (Mg,Fe,Al)]Σ = 4[Si2O7][SiO4]3(O,F) (OH,O)2, is a newly identified mineral from the Trimouns talc deposit, Luzenac, Ariege, French Pyrenees. The mineral occurs as striated colorless crystals finely intergrown with minute lamellae of tornebohmite (Ce). Associated minerals include pyrite, aeschynite-(Y), dolomite, tornebohmite-(Ce), dissakisite(Ce), talc, and quartz. Gatelite-(Ce) is insoluble in HCl, relatively hard (Mohs harness 6-7), brittle with irregular fracture, and exhibits good {100} and imperfect {001} cleavages. Gatelite-(Ce) is monoclinic, space group P21/a, with the following unit-cell parameters: a = 17.770(4), b = 5.651(1) c = 17.458(4) Å, β = 116.18(2)° V = 1573.3(6) Å3 Z = 4. The strongest five powder-diffraction lines [d in Å (I/Io) (hkl) are 15.67 (87) (001); 3.49 (50) (4̄12); 2.97 (100) (2̄15); 2.83 (44) (020); and 2.61 (56) (6̄12). Electron-microprobe analysis supported by single-crystal structure determination yielded the following empirical formula: (Ca1.09 La0.54 Ce1.36 Pr0.14 Nd0.75 Sm0.11 Dy0.01 Y0.04)Σ4.04(Al3.06 Mg0.51Fe2+ 0.32 Nb0.01)Σ3.90 Si5.06 O20.26(OH)1.60 F0.14. The calculated density (from the empirical formula) is 4.51 g/cm3. The structure was solved by direct methods and refined to Robs = 4.65%. It consists of edge sharing octahedral chains running along the b axis, cross-linked by SiO4 Si2O7 groups. The remaining large cavities are occupied by Ca and REE. The structure of gatelite-(Ce) can be easily described as a regular alternance of slabs of epidote-type structure (E) and slabs of tornebohmite-type structure (T) parallel to the (011) plane. Gatelite-(Ce) can be regarded as a ET polisome within a polysomatic series having epidote and tornebohmite as end-members.
Sections:New minerals
Subjects:Bonding; Cerium; Crystal chemistry; Crystal structure; Epidote; Epidote group; Formula; Hydrogen; Metals; Orthosilicates; Physical properties; Rare earths; Silicates; Sorosilicates; Talc deposits; Unit cell; Valency; Europe; France; French Pyrenees; Pyrenees; Western Europe; Gatelite; Trimouns Mine
Abstract Numbers:03M/4551
Record ID:2003024318
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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