Orthorhombic. G = 4·0-4·8. H = 6. Black; vitreous lustre. Norway. ~Priorite.~ Dimorphous with Euxenite (_q.v._). Orthorhombic; isomorphous with Blomstrandine. G = 4·6-5·0. H = 6. Black; transparent in flakes. Swaziland, S. Africa. Pseudobrookite. Fe₄(TiO₄)₃, ferric orthotitanate. TiO₂ = 44-53%. Orthorhombic. G = 4·39-4·98. H = 6. Dark brown to black. Norway; France. _Pyrochlore._ A columbate of Ca and E, with Th, Fe, Ti, F, etc. E₂O₃ → 18; TiO₂ = 5-14%. Cubic. G = 4·2-4·36. H = 5-5¹⁄₂. Dark brown. Scandinavia; the Urals; Tasmania, etc. Pyrophanite. MnTiO₃, with traces of SiO₂. TiO₂ = 50-53%. Rhombohedral; isomorphous with Ilmenite. G = 4·537. H = 5. Deep blood-red; translucent; lustrous. Pajsberg, Sweden. _Retzian._ Hydrated arsenate of Mn´´, Ca, E. Cer + Yttr = 8-11%. Orthorhombic, usually in prisms. G = 4·15. H = 4. Brown; pleochroic; transparent. Province of Nordmarken, Sweden. _Rhabdophane_ (Scovillite). Hydrated phosphate of E, Al, Fe, Mg, etc., with SiO₂. Cer = 53·8-57; Yttr = 2·1-10·0%. Massive. G = 3·94-4·01. H = 3¹⁄₂. Brown to yellow; translucent. Cornwall; Scoville, Connecticut, U.S.A. Rhönite. (Na,K,H)₃Ca₃(Fe´´,Mg)₁₅(Al,Fe´´´)₁₆(Si,Ti)₂₁O₉₀. TiO₂ = 9·5%. Anorthic, isomorphous with Aenigmatite. G = 3·5-4·3. Brown, with strong pleochroism. Rhön Mountains, Saxony. _Rinkite._ A titanosilicate closely allied to Mosandrite and Johnstrupite (_q.v._)--Na₉Ca₁₁Ce₃(Ti,Th)₄₁Si₁₂O₄₆? Cer = 21; Yttr = 0·4-1·4; TiO₂ = 13-14%. Monoclinic, very close to Johnstrupite. G = 3·46. H = 5. Yellow, pleochroic; translucent. Kangerdluarsuk, Greenland. ~Risörite.~ An yttria columbate, near Fergusonite, but with no U and considerable TiO₂; Yttr = 37; Cer = 2·9-4·0; TiO₂ = 6·5%. No data yet determined. Isotropic. G = 4·179. H = 5¹⁄₂. Yellowish brown. Norway. _Rogersite._ Hydrated yttria columbate. Yttr = 60·12%. A weathered Samarskite? Amorphous, mamillary. G = 3·313. H = 3¹⁄₂. White. Mitchell Co., N. Carolina. _Rosenbuschite._ Titanosilicate of Ca, Zr, Na, E, Fe, Mn, with F. ZrO₂ = 18·7-20; Cer = 0·3-2·4%. Monoclinic, in spherical aggregates. G = 3·30-3·31. H = 5-6. Orange-grey. Near Brevik, Sweden. _Rowlandite._ Silicate of E, with Th, Ti, Fe, etc.--2Y₂O₃, 3SiO₂. Cer = 14·4; Yttr = 47·7; ThO₂ = 0·6%. Massive. G = 4·515. H = 6. Pale dull green. Llano Co., Texas. ~Rutile.~ Titanium dioxide; TiO₂ = 98-100% Tetragonal; habit prismatic. G = 4·18-4·25. H = 6-6¹⁄₂. Reddish-brown to black. Very widely in Europe and America. ~Samarskite.~ R´´₃R´´´₂(Cb,Ta)₆O₂₁, where R´´ = Fe, Ca, UO₂; R´´´ = E. Cer = 1·2-6·4; Yttr = 4·72-21·2; ThO₂ + ZrO₂ → 7%. Orthorhombic; usually massive. G = 5·6-5·8. H = 5-6. Deep velvet black; opaque. Miask; Urals; Mitchell Co., N. Carolina. Schorlomite. A titaniferous Garnet--3CaO,(Fe,Ti)₂O₃,3(Si,Ti)O₂. TiO₂ = 12·5-22%.