It is found at Bourg d’Oisans in Dauphiné, and in Norway, the Urals, Brazil, etc. In Switzerland it occurs as the variety Wiserine, which was at one time believed to be xenotime. It was named Octahedrite by de Saussure, in 1796, from the prevailing habit, and Oisanite, from its occurrence in Dauphiné, by Delamètherie, in 1797. The name anatase (ανατασις = erection) was proposed by Haüy, being intended to denote that the vertical axis (_c_ : _a_) is greater than that of rutile, the other tetragonal modification of the dioxide. ~Brookite~, the third form of this compound, is orthorhombic. _a_ : _b_ : _c_ = 0·8416 : 1 : 0·9444. Common forms--the three pinakoids _a_ {100}, _b_ {010}, and _c_ {001}, prisms _m_ {110}, _l_ {210}, pyramids _e_ {122}, _z_ {122}, and numerous others. Angles--(100) ∧ (110) = 40° 5´; (001) ∧ (100) = 48° 18´; (001) ∧ (011) = 43° 22´. The habit is varied; it occurs usually in bipyramids with _e_ and _m_ or prismatic with _m_, _a_, and terminating pyramids. Cleavage ∥ _m_ indistinct, ∥ _c_ very poor. Hardness 5¹⁄₂-6; sp. gr. 3·87-4·01. Lustre metallic. Colour brown to reddish- and yellowish-brown and black. The optical behaviour is interesting. The acute bisectrix is perpendicular to _a_ (100), but while for red light the plane of the optic axes is (001), for blue it is (010); for an intermediate light, therefore (λ = 5550 µµ), the mineral appears uniaxial. The chief localities are Bourg d’Oisans, Miask, the St. Gothard, the Tyrol, Magnet Cove in Arkansas, and Tremadoc in Wales. Titanium dioxide can be obtained crystalline by the action of steam on titanium tetrafluoride, TiF₄, at high temperatures; it is stated that by varying the temperature of the reaction, any one of the three crystalline modifications can be obtained. * * * * * The only other minerals which need be mentioned in this class (see list) are: _Zirkelite_, a complicated mixture of oxides, in which thoria, zirconia, and titanium dioxide act as acidic oxides, and _Mackintoshite_, a mixture of several oxides, of which those of thorium and uranium are the most important. (_b_) THE CARBONATES ~Lanthanite~, Hydrocerite.--This mineral is a carbonate of ceria earths, chiefly lanthana, of the formula La₂(CO₃)₃,9H₂O. Orthorhombic; _a_ : _b_ : _c_ = 0·9528 : 1 : 0·9023. Common forms--the pinakoids _a_ {100} and _c_ {001}, with _m_ {110} and _o_ {111}. Angles--(100) ∧ (110) = 43° 37´; (001) ∧ (101) = 43° 26¹⁄₂´; (001) ∧ (011) = 42° 3¹⁄₂´. Habit tabular, parallel to _c_; cleavage perfect, ∥ _c_. Double refraction negative; optic axis plane _a_ (100). Usually amorphous, being probably an alteration product of a mineral rich in lanthanum. Hardness 2; sp. gr. 2·6-2·7. Colour white to yellowish-white, usually opaque; infusible before the blowpipe (being converted to the oxide), readily soluble in acids.