Cubic; usually massive. G = 3·81-3·88. H = 7-7¹⁄₂. Black; transparent in flakes. Magnet Cove, Arkansas. Senaite. (Fe,Mn,Pb)O,TiO₂, cf. Ilmenite. TiO₂ = 49-52%. Rhombohedral; isomorphous with Ilmenite, Geikielite, etc. G = 5·3 (to 4·2 when weathered). H = 6¹⁄₂. Black. Diamantina, Minas Geraes, Brazil. ~Sipylite.~ Columbate of E, Zr, Fe, U, Sn, etc.; near Fergusonite (_q.v._). Cubic, in octahedra. Usually granular. G = 4·89. H = 6. Brownish-black; translucent. Amhurst Co., Virginia. _Steenstrupine._ A silicate of E, Fe, Na, Th, Mn, Al, Ti, H₂O, etc.; near Melanocerite. Cer = 14·4-32·5; Yttr = 0-15·9; ThO₂ = 2·1-7·1%. Rhombohedral. G = 3·38. H = 4. Brown; faces dull. Kangerdluarsuk, Greenland. Strüverite. FeO,(Nb,Ta)₂O₅,4TiO₂. TiO₂ = 69-71%. Tetragonal; angles very close to those of rutile. G = 5·0. H = 6-7. Black; opaque. Craveggia, Piedmont, Italy; and in Madagascar. _Tachyaphaltite._ An altered zircon, containing H₂O. ZrO₂ = 40-50%. Tetragonal; very close to Zircon. G = 3·6. H = 5¹⁄₂. Dark brown. Kragerö, Norway. _Tengerite._ Hydrated carbonate of E, Be, Ca, etc.; a weathered Gadolinite (_q.v._). E₂O₃ = 39·2-47·8%. Amorphous. White; opaque; very soft. Llano Co., Texas. ~Thalenite.~ H₂E₄Si₄O₁₅, with traces of Fe´´´ and Al. Yttr = 58·6-63·9%. Monoclinic. G = 4·23. H = 6¹⁄₂. Bright red and yellow, Österby, Sweden. ~Thorianite.~ Mixed ThO₂ + UO₂, with E, Pb, Zr, Si, Fe, etc. ThO₂ = 72-79; Cer = 1-8%. Rhombohedral; pseudocubic. G = 8·0-9·7. H = 7. Jet black; bright resinous lustre. Gem-gravels of Ceylon. ~Thorite.~ ThSiO₄, with H₂O, U, Fe, E, Ca, Al, etc. ThO₂ = 41·4-57·9; E₂O₃ = 0-6%. Tetragonal; habit prismatic. G = 4·4-4·8; H = 4¹⁄₂-5. Brown to black. Various localities in Scandinavia. _Thorogummite._ UO₃,3ThO₂,3SiO₂,6H₂O? An altered Mackintoshite (_q.v._)? ThO₂ = 41·4; E₂O₃ = 6·7%. Usually massive; sometimes in crystals resembling Zircon. G = 4·43-4·54. H = 4-4¹⁄₂. Dull brown; opaque. Llano Co., Texas. ~Thortveitite.~ E₂O₃,2SiO₂, with Fe´´´, Al, Mn´´´ traces; E = chiefly Sc. Yttr = 54·5%. Orthorhombic, in radial aggregates. G = 3·571. H = 6-7. Greyish green; translucent. Iveland, Sätersdalen, Norway. ~Titanite~ (Sphene, Grothite). CaSiTiO₅, with Fe´´, Mn´´. TiO₂ = 34-45% (usually 41%). Monoclinic; wedge-shaped. G = 3·40-3·56. H = 5-5¹⁄₂. Yellow, green, or brown; pleochroism strong; lustre resinous. Widely distributed in Europe and N. America. Titanium Olivine. (H₂,Fe´´,Mg)₂(Si,Ti)O₄; Mn and F in traces. TiO₂ = 3-12%. Orthorhombic. G = 3·25-3·27. H = 6¹⁄₂-7. Deep red to yellow; pleochroic. Pfunders, Tyrol; Zermatt, Switzerland. _Tritomite._ A fluo-borosilicate of E, Th, Ca, with Zr, Na, H₂O, etc. Cer = 44·2-59·2; Yttr = 0·4-4·6; ThO₂ + ZrO₂ = 0-10·6%. Rhombohedral; in crystals resembling regular tetrahedra.