842 Mr Wohler 07i Pyrochlore^ a new Mineral Species. 



5^2.58, lead 31.34, antimony 44.39, copper 0.42 = 99.23. The 

 Jamesonite, like the »inkenite, consists principally of sulphate 

 of antimony and sulphate of lead, but in different proportions. 

 Three analyses of Jamesonite afforded the following results : 



First. 

 Sulphur, - - 22.15 



Lead, - - 40-75 



Lead, with traces of iron and zinc, 

 Copper, - - 0.13 



Iron, - - 2.30 



Antimony, - - 34.40 



34.40 parts of antimony in the first analysis, combined with 

 12.8*7 parts of sulphur, to form the sulphuret of antimony, and 

 40.75 parts of lead, with 6.33 parts of sulphur, to form sulphu- 

 ret of lead. The excess of sulphur, 2.95 parts, is nearly suffi- 

 cient to form, with the iron, sulphuret of iron. Although the 

 quantity of sulphuret of iron in Jamesonite is considerable, I 

 still consider it as accidental, because neither iron nor lead, in the 

 oxidated or sulphuretted state, combine together ; the crystal- 

 lised Fahlerz, for example, in which sulphuret of iron occurs, 

 never contains sulphuret of lead, even when the tetrahedrons of 

 Fahlerz are imbedded in lead-glance. The true composition of 

 Jamesonite may be expressed by the formula 3P& S" -f 4S& S" ; 

 the sulphuret of antimony in it containing double the quantity 

 of sulphur, as the sulphuret of lead. 



II. On Pyrochhre, a new mineral species. 



Pyrochlore occurs in the neighbourhood of Friederich- 

 schwarn in Norway, in zircon-syenite, where it was first found 

 by Dr Tank. Dr Wohler, during his journey with Berzelius 

 and Brongniart, met with this mineral near to Laurvig, in veins 

 in zircon-syenite. Berzelius proposes to name it Pyrochlore^ in 

 order to distinguish it from Polymignite, which, before the blow- 

 pipe, retains its black colour, while the pyrochlore becomes yel- 

 low. Its colour is reddish-brown, like brown titanite, and on 

 the fresh fracture appears almost black : — in thin splinters, is 

 translucent ; in thicker pieces opaque. It crystallises in regular 

 octahedrons. It is generally imbedded in felspar, sometimes in 

 Elaolite. Its specific gravity = 4.206 — 4.216,— i?o*^. It 

 scratches fluor-spar, but is scratched by felspar. Its streak is 



