[90]— Baddeleyite consists of almost pure zirconia (ZrO₂ = 96·5 per cent.) with small quantities of ferric oxide, alumina, lime, magnesia, alkalies and silica. Thoria and rare earths are present in traces, uranium is absent; the mineral is not radioactive, and contains only traces of helium.
[90] Vide Fletcher, Min. Mag. 1893, 46, 10, 148; Hussak, Zeitsch. Kryst. Min. 1895, 24, 164, and 25, 298.
Monoclinic—a : b : c = 0·9871 : 1 : 0·5114. β = 98° 451⁄2´.
Common forms—all three pinakoids, a {100}, b {010}, and c {001}, with the hemi-prisms m {110}, k {120}, and l {230}, and various pyramids and domes.
Angles—(100) ∧ (110) = 44° 171⁄2´; (100) ∧ (001) = 81° 141⁄2´; (100) ∧ (101) = 55° 331⁄2´.
Cleavage ∥ c and ∥ b, parting ∥ m due to repeated twinning. Twinning is exceedingly common; of many hundred crystals examined by Hussak, only three were found untwinned. Twin planes m (110), a (100), and x (201).
Colour brown, varying in zones by twinning, with distinct pleochroism. Hardness; sp. gr. varies from 4·4 to 6·0, being about 5·5 to 5·6 for fairly pure material. Double refraction negative, 2 E = 70-75°. Acute bisectrix nearly coincident with c axis, plane of the optic axes b, (010).
The mineral is insoluble in acids, readily soluble in fused potassium hydrogen sulphate. Before the blowpipe it is almost infusible; it dissolves in the fused borax bead, rapid cooling causing separation of crystals. If a bead containing zirconia be heated until the borax is partially volatilised, zirconia crystallises on cooling in tetragonal crystals, isomorphous with those of rutile.[91]
[91] Nordenskiöld, Pogg. Ann. 1861, 114, 625; for tetragonal zirconia see also Troost and Ouvrard, Compt. rend. 1888, 102, 1422.
The mineral was discovered in 1892 by Hussak and L. Fletcher independently. The former, who obtained it from the pyroxenite sand of São Paulo, South Brazil, believed it to be a tantalo-columbate, and called it Brasilite. Fletcher found it in a gem-gravel from Rakwana, Ceylon, and named it Baddeleyite. An analysis by Blomstrand of Hussak’s mineral showed it to be identical with the Ceylon mineral, and Hussak withdrew his name and accepted Fletcher’s. It has recently been found[92] in a corundum-syenite, near Bozeman, Montana, U.S.A.