[93] Friedel et Grandjean, Bull. Soc. franc. Min. 1909, 32, 52.
As an accessory rock mineral, and also as an important constituent of many sands, rutile is of very wide distribution. It occurs, usually imbedded in quartz or felspar, in many granites, syenites, gneisses, slates, and allied rocks; in acicular crystals penetrating quartz it forms the ‘Veneris Crinis’ of Pliny. At Risör and other localities in Norway, it is found in the massive form, and it is largely worked at Risör as a source of titanium. It occurs in all the countries of Europe, and largely in America. Arendal, Kragerö, and Risör, in Norway, the Binnenthal, the Urals, the St. Gothard, Castile, Magnet Cove in Arkansas, Alexander Co. in N. Carolina, Barre and Shelburne in Massachusetts, and Chester Co. in Pennsylvania are the chief localities.
It was in this mineral that the element titanium was first recognised by Klaproth (1795).
Anatase (Octahedrite)
is the second crystalline modification of titanium dioxide.
Tetragonal c = 1·7771. (001) ∧ (101) = 60° 38´, (111) ∧ (11̅1) = 82° 9´.
Common forms—Prisms a {100} and m {110}, pyramids p {111}, e {101}, and many other complex forms; the basal plane c {001} is occasionally found. Habit usually octahedral, with p or v prominent; sometimes tabular with c, more rarely prismatic with a well developed. Cleavage ∥ c and p perfect. Hardness 51⁄2-6; sp. gr. 3·82-3·95, usually increasing after heating. Lustre adamantine, so splendent that in Brazil detached crystals have been mistaken for diamonds. Colour, some shade of bluish-black to brown; by transmitted light, greenish-yellow. Transparent to opaque. Double refraction negative, strong; for sodium light ω = 2·554, ε = 2·493.
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.