~Yttrocrasite.~[55]--This is a complex titanate of rare earths (chiefly yttria earths) with lime, thoria, and oxides of lead, iron, uranium, etc.; it has a considerable water content. An approximate formula is R´´O,R^{iv}O₂,3R´´´₂O₃,16TiO₂,6H₂O, where R´´ = (Ca,Pb,Fe), R^{iv} = (Th,U), and R´´´₂O₃ = rare earths. No constitutional formula can be given; it will be noticed that the amount of titanium dioxide is considerably more than is required to combine with the bases present (cf. also Delorenzite below). It is radioactive. [55] Hidden and Warren, _Amer. J. Sci._ 1906, [iv.], ~22~, 515; also _Zeitsch. Kryst. Min._ 1907, ~43~, 18. Imperfect crystals only were found, apparently belonging to the orthorhombic system. No crystallographic data could be determined. The mineral is black, closely resembling polycrase and euxenite (_q.v._) in appearance. Hardness 5¹⁄₂-6; sp. gr. 4·80. It is infusible, and not easily soluble in acids. Hydrofluoric acid decomposes it, and the powdered mineral is also slowly attacked by boiling concentrated sulphuric acid. It was found in 1904 by Barringer, in Burnet Co., Texas. ~Delorenzite.~[56]--A compound similar to the above, but even richer in titanium dioxide, which amounts to 66 per cent. Tin dioxide is also present, with traces of columbic anhydride. The bases are the yttria earths (almost free from ceria earths), uranium dioxide, and some ferrous oxide, the formula being 2FeO,UO₂,2Y₂O₃,24TiO₂, with a little SnO₂ replacing TiO₂. It is strongly radioactive. Its closest chemical neighbour is yttrocrasite, but in appearance and angles it closely resembles polycrase (_q.v._). Its discoverer, Zambonini, therefore formulates it as a metatitanate with titanium acting also as a base--polycrase is a mixed metatitanate and metacolumbate--thus, 2FeTiO₃ + U(TiO₃)₂ + 2Y₂(TiO₃)₃ + 7(TiO)TiO₃. [56] Zambonini, _Zeitsch. Kryst. Min._ 1908, ~45~, 76. The crystals occur in aggregates of numerous individuals in sub-parallel growth. The system is orthorhombic; _a_ : _b_ : _c_ = 0·3375 : 1 : 0·3412. Usual forms--the pinakoids _a_ {100} and _b_ {010} with prism _m_ {110}, dome _d_ {201}, etc. Habit prismatic, elongated ∥ c axis. Hardness 5¹⁄₂-6; sp. gr. about 4·7. It was found with struvite in a pegmatite at Craveggia, Piedmont, Italy.