134 AiiahjsU df ike magyietical Pyrifex. 



iron, commonly called martial pyrites ; for the species and 

 varieties of this are found at all depths, and in all climates 

 and soils, whether antient, or of alluvial and recent fornia-r 

 tion. It is remarkable also, that, under certain circum- 

 stances, this sulphuret is daily produced in the humid way; 

 an instance of which, a few years back, I had the honour, 

 in conjunction with Mr. Wiseman, to lay before this so- 

 ciety * ; and although, in regard to pccuniarv value, the 

 pyrites of iron may be considered as comparatively insig- 

 nificant, yet there is every reason to believe, that in the 

 operations of nature it is a substance of very considerable 

 importance. 



§ 11. 



The species and varieties of martial pyrites arc in general 

 so well known, and have been so fre(|uently and accurately 

 described, as to figure, lustre, colour, and other external 

 characters, that it would be totally superfluous here to give 

 any detailed account of them. One of the species, how ever, 

 merits peculiar notice, as possessiiig the remarkable property 

 of strong magnetic polarity ; and, although it has been de- 

 scribed by modern mineralogists f,- it does not appear to 

 have been as yet subjected to any regular chemical exa- 

 mination ; so that, whether it be a sulphuret of iron inhe- 

 rently endowed with the magnetical property, or a sulphuret 

 in which particles of the ordinary magnetical iron ore are 

 simply but minutely interspersed, has to this time remained 

 undecided. 



This species is known by the w^vato't magiieilcal pyrites, 

 and is called by the Germans magnet-kies, ox Jtrrum iniuc- 

 ralixatum magiictico-pyritaceum. 



It is mt^t frequently of the colour of bronze, passing 

 to a pale cupreous red. 



The lustre is metallic. 



The fracture is unequal, and commonly coarse-grained, 

 but sometimes imperfectly conchoidal. 



The fragments are amorphous. 

 'The trace is yellowish gray, with some metallic lustre. 



It is not vtry hard; but, when struck with steel, sparks 

 are produced, although with some difficultv. 



It is brittle, and is easily broken. 



This pyrites has been hitherto found only in some parts 

 of Norway, Silesia, Bavaria, and especially at Geier, Mef- 



* Transactions of (be Royal Society of London for 17981 p. 567. 

 f Kirwan, vol. ii. p. 79. Widc-nmann, p. 792. Kmmcrling, ad edit, 

 ta.nt: ii. p. zS6. Karstcn, p. 48. Brochanc, tome ii. p. 231. 



fersdorf. 



