• Spratt, John

Abstract

<jats:title>Abstract</jats:title><jats:p>The new pyroxenoid barrydawsonite-(Y) occurs at the Merlot Claim, North Red Wine Pluton, Labrador, Canada (62°32'38.54'' W; 54°08'1.37'' N). The host rock is a metamorphosed eudialyte syenite consisting of eudialyte, potassic arfvedsonite, jadeitic aegirine, nepheline, albite and potassium feldspar with accessory Y-bearing pectolite, britholite and steenstrupine. Barrydawsonite-(Y) crystals commonly have discrete thin rims of Y-bearing pectolite. The average empirical formula (based on nine anions p.f.u.) is Na<jats:sub>1.54</jats:sub>Ca<jats:sub>0.74</jats:sub>Mn<jats:sub>0.15</jats:sub>Fe<jats:sub>0.07</jats:sub>Y<jats:sub>0.38</jats:sub>Nd<jats:sub>0.01</jats:sub>Sm<jats:sub>0.01</jats:sub>Gd<jats:sub>0.02</jats:sub>Tb<jats:sub>0.01</jats:sub>Dy<jats:sub>0.04</jats:sub>Ho<jats:sub>0.01</jats:sub>Er<jats:sub>0.02</jats:sub>Yb<jats:sub>0.01</jats:sub>Si<jats:sub>3.00</jats:sub>O<jats:sub>9</jats:sub>H. The simplified formula is Na<jats:sub>1.5</jats:sub>Y<jats:sub>0.5</jats:sub>CaSi<jats:sub>3</jats:sub>O<jats:sub>9</jats:sub>H. Barrydawsonite-(Y) is related to pectolite by the substitution ½[Na<jats:italic>M</jats:italic><jats:sup>3+</jats:sup>Ca<jats:sub>–2</jats:sub>] (<jats:italic>M</jats:italic><jats:sup>3+</jats:sup>= Y,<jats:italic>REE</jats:italic>), and is exceptional in being the only member of the pectolite group that has the structure of the monoclinic<jats:italic>M2abc</jats:italic>polytype. The crystal structure has been determined in monoclinic space group<jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>a: a</jats:italic>= 15.5026(2),<jats:italic>b</jats:italic>= 7.0233(1),<jats:italic>c</jats:italic>= 6.9769(1) Å, β = 95.149(1)°,<jats:italic>V</jats:italic>= 756.58(2) Å<jats:sup>3</jats:sup>(<jats:italic>Z</jats:italic>= 4). Final agreement indices are<jats:italic>R</jats:italic><jats:sub>1</jats:sub>= 0.038,<jats:italic>wR</jats:italic><jats:sub>2</jats:sub>= 0.068, Goof = 1.136. The asymmetric unit of barrydawsonite-(Y) has three metal sites:<jats:italic>M</jats:italic>(1) = Ca,<jats:italic>M</jats:italic>(2) = Na0.5(Y,REE)0.5,<jats:italic>M</jats:italic>(3) = Na.<jats:italic>M</jats:italic>(1) and<jats:italic>M</jats:italic>(2) are octahedrally-coordinated sites, whereas<jats:italic>M</jats:italic>(3) is [8]-coordinated as in pectolite and serandite. The structural formula for the empirical composition is<jats:sup><jats:italic>M</jats:italic>(3)</jats:sup>Na<jats:sub>1.00</jats:sub><jats:sup><jats:italic>M</jats:italic>(2)</jats:sup>(Na<jats:sub>0.50</jats:sub>Y<jats:sub>0.38</jats:sub><jats:italic>REE</jats:italic><jats:sub>0.13</jats:sub>)<jats:sub>Σ=1.01</jats:sub><jats:sup><jats:italic>M</jats:italic>(1)</jats:sup>(Na<jats:sub>0.04</jats:sub>Ca<jats:sub>0.74</jats:sub>Mn<jats:sub>0.15</jats:sub><jats:sup>2+</jats:sup>Fe<jats:sub>0.07</jats:sub><jats:sup>2+</jats:sup>)<jats:sub>Σ=1.00</jats:sub>Si<jats:sub>3</jats:sub>O<jats:sub>9</jats:sub>H. There is excellent agreement between the refined site-scattering values and those calculated based upon the structural formula.</jats:p><jats:p>Barrydawsonite-(Y) is biaxial (+) with α = 1.612(1), β = 1.617(1), γ = 1.630(1) (white light) and 2V = 63(1)°. The five strongest peaks in the X-ray powder diffraction pattern are [<jats:italic>d</jats:italic><jats:sub>obs</jats:sub>(Å),<jats:italic>I</jats:italic><jats:sub>obs</jats:sub>%, (hkl)]: [2.905, 100, (023)], [3.094, 30, (210,211,121,202)], [1.7613, 29, (127,323,040)], [3.272, 27, (202,104)], [1.7016, 27, (140,227,325)].</jats:p>

Topics

• impedance spectroscopy
• Potassium
• space group