406 PHYSIOGRAPHY. CLASS II, 



Fundamental form. Rhombohedron. Vol. I. Fig. 7. 



Simple forms. R QD (P) ; R (a) ; R + QD ( d) ; 

 P + ntf); P+oo(JW> 



Combinations. 1. R co. P -|- QD. 2. R oo. 

 P. P -f OD. Sim. Fig. 112. Inclination of P on 

 a = 135 ; of P on e = 102 13', BOUENON. 



Cleavage, R oo perfect ; P -fc- GO less distinct. 

 Fracture small and imperfect conchoidal. Sur- 

 face rougb, particularly P + oo, sometimes also 

 horizontally streaked. Subject to tarnish. 



Lustre metallic. Colour intermediate between 

 bronze-yellow and copper-red. Streak dark 

 greyish-black. 



Slight action on the magnet. Brittle. Hardness 

 = 3-5 ... 4-5; Sp. Gr = 4-631, of a cleavable 

 variety. 



Compound Varieties. Massive: composition 

 granular, individuals of various sizes, or even im- 

 palpable. Fracture uneven. 



OBSERVATIONS. 



1. The varieties of the present species have been divid- 

 ed into Foliated and Common Magnetic Pyrites, which are 

 easily distinguished from one another, as their division 

 depends upon one single character, the presence of cleavage 

 in the former, and the want of it in the latter, on account 

 of the too small size of the component individuals. 



2. One analysis by HATCHETT, and two by STROME.YER, 

 have yielded the following proportions : 



Iron 63-50 59-85 5S-37. 



Sulphur 36-50 40-15 43-63. 



The first of these is expressed by Fe S 2 , which contains 

 62'77 iron, and 37*23 sulphur ; the others are considered- 



