Publication Type:

Journal Article

Authors:

McDonald, Andrew M.; Chao, George Y.

Source:

The Canadian MineralogistThe Canadian Mineralogist, Mineralogical Association of Canada, Ottawa, ON, Canada, Volume 48, Number 2, p.267-278 (2010)

ISBN:

0008-4476

Keywords:

aegirine, alkali feldspar, borosilicates, breccia, Canada, chain silicates, chemical composition, Clinopyroxene, crystal structure, eastern canada, feldspar group, formula, framework silicates, igneous rocks, labuntsovite, microcline, mineral assemblages, Mont-Saint-Hilaire Quebec, neptunite, nesosilicates, new minerals, orthosilicates, pyroxene group, pyrrhotite, quebec, ring silicates, Rouville County Quebec, silicates, sodalite, sodalite group, space groups, sulfides, x-ray diffraction data, zircon, zircon group

Abstract:

Rogermitchellite is a new, complex species of zirconosilicate found in igneous breccia at the Poudrette quarry, Mont Saint-Hilaire, Quebec. It is associated with aegirine, annite, galena, a labuntsovite-group mineral, manganoneptunite, microcline, pyrrhotite, sodalite and zircon. Paragenetically, the mineral crystallizes after aegirine and before microcline. Isolated, single crystals are colorless to grey, prismatic along [001], and slightly flattened perpendicular to this direction, with a maximum dimension of 0.1X0.25 mm. It develops as euhedral crystals displaying the prominent forms prism {100} and pinacoid {001}, with a minor, very shallow ditrigonal scalenohedron {10l}. The mineral is transparent with a vitreous luster and a white streak and is non-luminescent. The Mohs hardness is 5, and no cleavage is evident. It is brittle with a conchoidal to splintery fracture. The calculated density is 3.34 g/cm (super 3) . Rogermitchellite is non-pleochroic, uniaxial positive, with omega 1.640(1) and epsilon 1.663(1). Four analyses made on one crystal gave, as an average: Na (sub 2) O 3.45, CaO 0.10, SrO 18.54, BaO 5.18, B (sub 2) O (sub 3) (calc.) 2.34, SiO (sub 2) 39.12, ZrO (sub 2) 26.39, TiO (sub 2) 0.63 and H (sub 2) O (calc.) 6.96, for a total of 102.71 wt.%. The empirical formula, based on 288 anions and the sum of (Si+B)=90 apfu, is: Na (sub 12) (Sr (sub 21.16) Na (sub 1.17) Ca (sub 0.21) ) (sub Sigma 22.54) Ba (sub 4.00) (Zr (sub 25.33) Ti (sub 0.93) ) (sub Sigma 26.26) (Si (sub 77.02) B (sub 0.98) ) (sub Sigma 78) B (sub 12) O (sub 246) (OH) (sub 24) .18H (sub 2) O or, ideally, Na (sub 12) Sr (sub 24) Ba (sub 4) Zr (sub 26) Si (sub 78) B (sub 12) O (sub 246) (OH) (sub 24) .18H (sub 2) O. The mineral is trigonal, space group P3c1, a 26.509(4), c 9.975(2) Aa, V 6070.6(1) Aa (super 3) and Z=1. The strongest six lines on the X-ray powder-diffraction pattern [d in Aa(I)(hkl)] are: 2.760(100)(442), 3.761(90)(402), 1.991(70)(444), 3.150(50)(441), 5.762(40)(400) and 3.924(30)(312). The crystal structure was refined to R=4.62% and wR (super 2) =12.73% for 1588 reflections [F (sub o) > 4sigma (F (sub o) )]. It consists of pairs (Si (sub 3) O (sub 9) ) rings (offset 30 degrees relative to one another along [001]) linked to isolated ZrO (sub 6) octahedra in a motif similar to that in benitoite. Additional (Si (sub 3) O (sub 9) ) and [Si (sub 2) BO (sub 7) (OH) (sub 2) ] rings along with ZrO (sub 6) octahedra complete a three-dimensional heteropolyhedral framework. Channels along [001] within this framework are occupied by Ba, Na, (Sr+Na) and H (sub 2) O. Rogermitchellite has chemical and crystal-structure features common to benitoite, wadeite and catapleiite, and should be considered as a structural hybrid of these minerals. It possesses additional features (presence of essential B, Sr, H (sub 2) O; trigonal symmetry) that make it unique.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2010-064038<br/>benitoite<br/>Poudrette Quarry<br/>rogermitchellite<br/>zirconosilicates