G = 4·15-4·25. H = 5¹⁄₂. Dark brown; transparent to opaque. Langesund Fiord, Norway. _Tscheffkinite._ Titano-silicate of E, Th, Fe, Ca, etc. Cer = 23-47; Yttr = 0-3·4; ThO₂ + ZrO₂ = 0-20; TiO₂ = 16-21%. Massive, amorphous. G = 4·26-4·55. H = 5-5¹⁄₂. Velvet black. Ilmen Mountains; Nelson Co. and Bedford Co., Virginia, U.S.A. _Tysonite._ Fluoride of E, with Th, H₂O, CO₂, etc. Cer = 69·2-70·6; ThO₂ = 0-31%. Hexagonal; in thick prisms. G = 6·12-6·14. H = 4¹⁄₂-5. Wax yellow; transparent to translucent. Fahlun and Österby, Sweden; Pike’s Peak, Colorado. _Uhligite._ Titanate of Zr, Ca, Al; Ca(Zr,Ti)O₃ + Al(Ti,Al)O₃? TiO₂ = 48; ZrO₂ = 22%. Cubic; near to Perovskite (_q.v._). H = 5-6. Black. Transparent in flakes. Lake Magad, E. Africa. ~Uraninite.~ Oxides of U (60-75%), with PbO₂, ThO₂, ZrO₂, E₂O₃, Fe₂O₃, etc. Cer. = 0-2·7; Yttr = 0-10·2; ThO₂ = 1·6-11·1; ZrO₂ = 0-8·1%. Cubic, usually massive; alters to amorphous pitchblende. G = → 6·4 (massive); → 9·7 (crystalline). H = 5¹⁄₂. Black; transparent in splinters. Norway; Bohemia; Saxony; Cornwall; Carolina, etc. _Vietinghofite._ A hydrated ferruginous samarskite (_q.v._). E₂O₃ = 8·2; ZrO₂ = 1·0%. Amorphous. G = 5·53. H = 5¹⁄₂-6. Dull black; opaque. Lake Baikal, Siberia. Warwickite. 6MgO,FeO,2TiO₂,3B₂O₃? TiO₂ = 23·5%. Orthorhombic; habit prismatic, elongated. G = 3·35-3·36. H = 3-4. Dark brown to black; pleochroic. Double refraction strong, +ve. Edenville, New York State. _Weibyite._ Carbonate of E, with Ca, Sr, F, and H₂O; allied to Bastnäsite (_q.v._). Cer = 66·96%? Orthorhombic; in pyramids resembling those of Zircon. Crystals are small, and covered with a thin yellow crust; they are intergrown with Parisite (_q.v._) Langesund Fiord, Norway. ~Wiikite.~ Titano-tantalo-silicate of Zr, Th, E, Fe, U, with Cb₂O₅, H₂O, etc. Cer = 2·5; Yttr = 7·6; Sc₂O₃ = 1·2; ThO₂ = 5·5; ZrO₂ + TiO₂ = 23·4%. Perfectly amorphous. G = 4·85. H = 6. Black; opaque; infusible. Impilaks, Lake Ladoga, Finland. _Wöhlerite._ Silicate and columbate of Ca, Zr, Na; Si₁₀Zr₃Cb₂O₄₂F₃Ca₁₀Na₅? ZrO₂ = 15·2-22·7%. Cer, traces. Monoclinic; prismatic or tabular habit. G = 3·41-3·44. H = = 5¹⁄₂-6. Light yellow; pleochroic. Langesund Fiord. ~Xenotime.~ Phosphate of E, with ThO₂, SiO₂, Zr, etc. Cer = 0-11; Yttr = 54·1-64·7; ThO₂ = 1-5%. Tetragonal; isomorphous with Zircon? G = 4·45-4·56. H = 4-5. Brown to yellow; opaque. Diamond sands of Brazil; Norway. _Yttrialite_ (Green Gadolinite). A weathered gadolinite (_q.v._)--E₂O₃,2SiO₂. Cer = 6·6-8·2; Yttr = 43·4-46·5; ThO₂ = 10·8-12·8%. Amorphous, massive. G = 4·6. H = 5¹⁄₂. Green to brown; translucent. Bluffton, Llano Co., Texas. ~Yttrocerite.~ Ca₃E₂F₁₂, 1¹⁄₂H₂O. Cer = 9·3-18·2; Yttr = 8·1-29·4%. Massive, granular. G = 3·45. H = 4¹⁄₂. White to violet blue or brown. Various localities in Scandinavia.