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