Mineralogy. 359 



sular system, being regular octahedrons, according to the measurements 

 by Professor Gustavus Rose. It presents no cleavage, but a rather perfect 

 conchoidal fracture, with a considerable degree of a kind of lustre interme- 

 diate between the resinous and vitreous. The surface of the crystals is less 

 bright. It is of a reddish-brown colour, often very dark, and resembling brown 

 sphene, a substance which it is very nearly allied to in respect to simila- 

 rity. It is slightly translucent only on its sharp edges. Larger fragments 

 appear entirely opaque. It affords a pale brown streak. Its hardness is in- 

 termediate between that of fluor and felspar, or = 5.0. Its specific gra- 

 vity = 4.206 — 4.216, according to G. Rose. 



It occurs in the zircon-syenite of Fredriksvarn and Laurvig in Norway 

 almost always in crystals of the size of a pea and smaller, often so firmly 

 attached to the surrounding felspar, or elaolite, that they cannot be sepa- 

 rated from them in their faces of crystallization. It was first noticed in 

 the rocks near Fredriksvarn as a particular substance by Mr Tank, who 

 likewise discovered the polymignite and the phosphate of yttria, and it was 

 found also near Laurvig by Messrs Berzelius, Brongniart, and Woehler, 

 during a journey which they made through Norway. The name of pyro- 

 chlore was proposed by Berzelius in allusion to its property of turning 

 yellow when exposed to the blast of the blowpipe, a property not found in 

 polymignite, with which it often is associated. 



The above description was given by Dr Woehler, who examined the 

 chemical constitution of the substance, and therefore has the merit of 

 having established, both as a mineralogical species and a peculiar chemical 

 compound, a substance which had long ago been noticed by mineralogists 

 under erroneous names, or confounded with other bodies. 



It shows the following phenomena when treated with the blowpipe. 

 Heated alone it becomes pale brownish-yellow, but retains its lustre, and 

 melts with great difficulty into a blackish-brown scoria. 



It is perfectly dissolved by borax. The globule obtained in the oxida- 

 ting flame is reddish-yellow and transparent, but becomes easily opaque 

 and yellow by flaming. The globule turns opaque and white on cooling, 

 if a large quantity of the mineral has been employed. In the reducing 

 flame the globule is deep red, similar to the colour produced by titanium 

 containing iron, but by flaming it forms a pale bluish-grey enamel, often 

 with stripes of a pure blue colour. 



It effervesces with salt of phosphorus, but is likewise perfectly soluble 

 in it. In the oxidating flame the globule is yellow while hot, but gene- 

 rally becomes grass-green on cooling. In the reducing flame this green 

 colour soon disappears, and is superseded by a deep red one, inclining to 

 violet-blue, as from titanic acid mixed with a little iron. If again expos- 

 ed to the oxidating flame, the green tint returns, which is like that from 

 uranium.* 



With soda on a platinum leaf the green colour produced by manganese 

 is visible. 



• There is a mineral occurring along with pyrochlore nearly resembling it. but 

 giving before the blowpipe only the reactions of uranium. From the want of ajsuf- 

 ticient supply of mineral it was not analyzed. 



