No special advantages are claimed for the system of classification, which is merely one of convenience. The minerals are divided into five groups:-- (1) The Silicates, which are grouped into three sub-divisions. (2) The Titano-silicates and the Titanates. (3) The Tantalo-columbates, sub-divided into those free from titanium and those in which titanium is present. (4) The Oxides and Carbonates. (5) The Halides and Phosphates. A separate chapter has been devoted to the monazite sands, and another to the radio-active properties of the minerals. ALPHABETICAL LIST OF MINERALS CONTAINING TITANIUM, ZIRCONIUM, THORIUM, OR ELEMENTS OF THE CERIUM AND YTTRIUM GROUPS. The following list contains all but a few entirely unimportant members of these classes of minerals. The names of those species selected for fuller treatment are printed in heavy type, whilst names of those not so selected, which for convenience are included under the generic term ‘Rare earth mineral,’ _i.e._ roughly all those containing Thorium, or elements of the Cerium and Yttrium groups, and the commoner Zirconium minerals, as distinguished from minerals containing Titanium, are printed in italics. (See footnote on p. 4.) Their properties are given in the following order:-- Chemical Composition and Rare Earth Content. Crystallographic Data. Physical Properties. Locality, etc. The following contractions are employed: E = any element or elements of the cerium or yttrium groups. Cer = oxides of the cerium metals. Yttr = oxides of the yttrium metals. G = Specific Gravity. H = Hardness. Aenigmatite. A Titanosilicate of Fe´´ and Na, with small proportions of Fe´´´ and Al´´´. Closely allied to the amphiboles. TiO₂ = 7-8%. Anorthic. Habit prismatic. G = 3·80-3·86. H = 5¹⁄₂. Black; pleochroism strong. Greenland and S. Norway. ~Aeschynite~ A Titanocolumbate of Cerium metals, with Th, Fe, Ca, Mn, aq. Cer = 19·4-24·1; Yttr = 1·1-3·1; ThO₂ = 15·7-17·6; TiO₂ = 21-22%. Rhombic, holosymmetric. Habit prismatic or tabular. G = 4·9-5·7. H = 5·6. Black; opaque. Hitterö, Norway; Miask, Urals; also in Germany and Brazil. ~Allanite~ (Orthite). H₂O, 4R´´O, 3R´´´₂O₃, 6SiO₂, where R´´ = Ca, Fe´´, Be, and R´´´ = Al, Fe´´´, E. An epidote containing rare earths. Cer = 3·6-51 (usually 10-25); Yttr = 0-8 (usually < 3); ThO₂ = 0-3·5%. Monoclinic; isomorphous with epidote. G = 3·5-4·2. H = 5¹⁄₂-6. Brown to black; opaque. Widely distributed in Greenland and Scandinavia. _Alvite_ (Anderbergite). Silicate of Zr and E, with Ca, Mg, Be, Al, Cu, Zn, and aq. in small quantities. Cer → 3·98; Yttr → 22; ZrO₂ = 30·5-61·4%. Tetragonal; optically isotropic. Pseudomorphous after zircon. G = 3·3-4·3. H = 5-6. Yellowish brown; transparent. Ytterby, Sweden; Arendal, Norway; various localities in N. America. ~Anatase~ (Octahedrite). Titanium dioxide. TiO₂ = 97-100%.