[95] _Amer. J. Sci._ 1911, [iv.], ~31~, 533. [96] _Abstr. Chem. Soc._ 1912, ~102~, ii. 773. * * * * * The following rare earth carbonates are described in the alphabetical list: _Ancylite_, a basic hydrated carbonate. _Tengerite_, a hydrated carbonate formed by the weathering of gadolinite. _Kischtimite_, a fluo-carbonate related to parisite. _Bastnäsite_ (Harmatite) and _Weibyite_, hydrated fluocarbonates of the cerium elements. CHAPTER VI THE PHOSPHATES AND HALIDES (_a_) THE PHOSPHATES ~Monazite~, Phosphocerite.--Monazite, by far the most important, commercially, of all the rare earth minerals, is essentially an orthophosphate of the ceria earths, of the formula R´´´PO₄.[97] The yttria earths are usually present in small quantities. Silica and thoria, in quantities varying from traces up to 6 per cent. of the former and from 1 to 20 per cent. of the latter, are invariable constituents; it is almost entirely to the percentage of thoria that the mineral owes its commercial value. The following also are common constituents, though usually in very small quantities only--stannic, ferric and manganous oxides, alumina, lime, magnesia, zirconia and water. Helium was observed in it by Tilden, and by Ramsay, Collie and Travers.[98] Boltwood[99] and Zerban[100] found uranium in it; the latter attributed this to impurities, the former regarded it as an essential constituent. Strutt[101] found uranium in a pure monazite. Haitinger and Peters[102] detected radium, their result being confirmed by Boltwood and Strutt. [97] For the composition of the earths in monazite, see James, _J. Amer. Chem. Soc._ 1913, ~35~, 235. [98] _Trans. Chem. Soc._ 1895, ~67~, 684. [99] _Phil. Mag._ 1905, [vi.], ~9~, 599. [100] _Ber._ 1905, ~38~, 557. [101] _Proc. Roy. Soc._ 1905, A, ~76~, 88 and 312. [102] _Sitzungsb. kaiserl. Akad. Wiss. Wien_, May, 1904. Monazite occurs in small crystals belonging to the monoclinic system. _a_ : _b_ : _c_ = 0·9693 : 1 : 0·9256, β = 76° 20´. These values vary slightly with different specimens. Common forms--Ortho- and clino-pinakoids _a_ {100}, _b_ {010}, hemi-prisms _m_ {110}, and _n_ {120}, hemi-ortho-prisms _w_ {101} and _x_ {1̅01}, hemi-clino-prism _e_ {011}, hemi-pyramid _v_ {1̅11}, etc.; the basal pinakoid _c_ {001} is rare. Angles--a ∧ _m_ = 43° 17´, _c_ ∧ _w_ = 37° 8´, _c_ ∧ _e_ = 41° 58´. Habit tabular, parallel to _a_, needle-shaped by elongation parallel to _b_ axis, or prismatic by good development of _v_. Cleavage ∥ _c_, perfect, ∥ _a_, distinct, ∥ _b_, difficult.