Home > Mineral Abstracts > CanMin Vol. 12, pp. 316-319 (1974)




Vol. 12, pp. 316-319 (1974)



Gaidonnayite, Na2ZrSi3O9 · 2H2O,
a new mineral
from Mont St. Hilaire, Quebec


G. Y. Chao and David H. Watkinson
Department of Geology, Carleton University,
Ottawa , Ontario K1S 5B6


ABSTRACT

          Gaidonnayite occurs at Mont St. Hilaire, Quebec, in miaroles in nepheline syenite both as crystals on analcime and in cavities in dense natrolite aggregates; it is mainly associated with hilairite, aegirine, calcite, and siderite.  Gaidonnayite also occurs in altered pegmatite dykes mainly with catapleiite, elpidite, hilairite, albite, microcline, chlorite, aegirine, epididymite, and goethite.

     The mineral is orthorhombic, space group P21nb, a = 11.740, b = 12.820 and c = 6.691Å.  Z = 4, D(calc.) = 2.10, D(meas.) = 2.67 g/cm3, H = 5.  It has conchoidal fracture and no noticeable cleavage.  The mineral is colourless, white to beige, with vitreous luster.  Crystals are bladed on (010), elongated along [100], bounded by {010}, {120}, and {100} with striations on {010} and {120} parallel to [001].  Twinning by [012]180°ยบ  is common.  The mineral is optically biaxial with a = 1.573, b = 1.592,
g = 1.599, 2Vz = 121°, X = a, Y = b and Z = c.

     Electron microprobe analysis gave:

SiO2 - 42.51
ZrO2 - 30.21
Nb2O5 - 3.00
TiO2 - 0.42

Na2O - 13.11
K2O - 2.20
H2O - 9.25
(by TGA to 1000°C)
Sum 100.70%


     The analysis corresponds to:


(Na1.72K0.19)(Zr1.00Nb0.09Ti0.02) Si2.88O9 · 10H2O


or ideally Na2ZrSi3O9 · 3H2O.

     Dehydration began immediately on thermogravimetric analysis and was complete at about 400°C; water lost was not re-absorbed on cooling.

     The mineral is a dimorph of catapleiite and is similar in many properties to a-catapleiite.



© 1974  The Canadian Mineralogist