Zinc- and Y-Group-Bearing Senaite from St Peters Dome, and New Data on Senaite from Dattas, Minas Gerais, Brazil

Eugene E. Foord, William N. Sharp and John W. Adams
US Geological Survey, Denver Federal Center, Denver, Colorado 80225, USA
705 Garland Street, Lakewood, Colorado 80215, USA

Abstract: A Zn- and Y-group-bearing senaite, formulated as (Pb0.63Na0.46Ba0.11)Σ1.20(Ti14.64Fe2.16+2Zn1.74Fe1.00+3Y‒groupREE0.70Mn0.38Nb0.20Sn0.03Zr0.03Th0.02)Σ20.9O38 , a member of the crichtonite group, is a newly characterized phase associated with murataite at the St Peters Dome area, Colorado. The Zn- and Y-group-bearing senaite is uranium-free and nonmetamict, but otherwise is comparable to known senaites and davidites in X-ray diffraction pattern, symmetry, and structure. The REE distribution shows a strong dominance of Y and the Y-group REE which are present in M(1). Megascopically, the mineral is black, submetallic, and opaque; in polished section it appears to be white and moderately bright compared with murataite. Cleavage is absent but twinning on {5270} is present.

Senaite and hitherto unreported zinc-bearing senaite from Dattas, Diamantina, Minas Gerais, Brazil, have the following respective structural formulas as determined by electron microprobe: (Pb0.76Sr0.20La0.08Ce0.07Ba0.04)Σ1.15(Ti12.89Fe5.99+3Mn0.88Y0.59Zn0.12Mg0.07Nb0.03Cr0.02Th0.02)Σ20.61O38 and (Pb0.89Ba0.15Ce0.02Sr0.02)Σ1.08(Ti14.57Fe2.86+3Zn1.76Na0.63Mn0.50Y0.28Nb0.14Mg0.04Cr0.02)Σ20.83O38

Mineralogical Magazine; March 1984 v. 48; no. 346; p. 97-106; DOI: 10.1180/minmag.1984.048.346.13
© 1984, The Mineralogical Society
Mineralogical Society (www.minersoc.org)