Home > Mineral Abstracts > CanMin Vol. 23, pp. 21-28 (1985)




Vol. 23, pp. 21-28 (1985)



Doyleite, a new polymorph of Al(OH)3,
and its relationship to bayerite,
gibbsite and nordstandite*


George Y. Chao and Judith Baker
Department of Geology, Carleton University,
Ottawa, Ontario K1S 5B6



Ann P. Sabina and Andrew C. Roberts
Geological Survey of Canada,
601 Booth Street, Ottawa, Ontario K1A 0E8


ABSTRACT

     Doyleite, a new polymorph of Al(OH)3, occurs with calcite and pyrite in albitite veins in nepheline syenite at Mont St. Hilaire, Quebec and in silicocarbonatite sills with weloganite, cryolite, calcite, quartz and other minerals at the Francon Quarry, Montreal, Quebec.  A wet-chemical analysis gave:  Al2O3 65.2, CaO 0.48, H2O (TGA to 1100°C) 35.76, sum 101.44 wt.%, corresponding to Al0.99Ca0.01(OH)3.00. The mineral is not attacked by 1:1 HCl, H2SO4 or HNO3 at room temperature.

     A single-crystal X-ray study showed the mineral from Mont St. Hilaire to be triclinic, space group P1 from morphology, a 5.002(1), b 5.175(1),
c 4.980(2) Å, a 97.50(1), b 118.60(1), g 104.74(1)°, Z = 2.  The strongest five X-rays powder-diffraction lines
[d in Å(I)(hkl)] are:


4.794 (100)(010)
2.360 (40)(101)
19.972 (30)(221)

1.857 (30)(111)
1.842 (30)(122)


     Crystals are tabular on (010), showing forms {010}, {101}, {101} and, occasionally, {100} and {001}.  They are white, creamy white or bluish white, transparent or translucent to opaque with a white streak.  Their lustre is vitreous, pearly or dull.  Mohs hardness 2½ - 3, D(meas.) 2.48, D(calc.) 2.482 g/cm3.  Cleavage is perfect on {010}, fair on {100}.  Optically, the mineral is biaxial positive, a 1.545 (1), b 1.553 (1), g 1.566 (1), 2V = 77° in Na light.  Orientation of indicatrix in spherical co-ordinates (f, r):  X(90°, 41°), Y(240°,53°), Z(343°,74°), with c(0,0) and b* (0,90°).  TGA showed a weight loss of 25.63% between 280 and 410°C, and a further gradual loss to 1000°C, giving a total weight loss of 35.76%.

     The infrared absorption spectum of doyleite is similar to but simpler than those of gibbsite and nordstrandite.  Its structure is predicted from the known structures of nordstrandite and gibbsite on the basis of similarities in X-ray precession photographs in two zones.  Polymorphism in Al(OH)3 results from different ways of stacking the layers of Al(OH)6 octahedra.   The mineral is named after E.T. Doyle of Ottawa, Ontario.

Keywords:  doyleite, aluminium hydroxide, new mineral, Mont St. Hilaire, Francon Quarry, Quebec, structural relationship, bayerite, gibbsite, nordstrandite.

* Publication 16-84 of the Ottawa-Carleton Centre for Geoscience Studies.


© 1985  The Canadian Mineralogist