Iron. 281 



tion of iron as to be worked with a view of 

 obtaining this metal ; it confifts of a mixture 

 of quartz and argill, with the calces of iron 

 and zinc ; its colour is yellow, red, or brown, 

 and it is moderately hard. 



SPECIES XVIII. 



Mineralized by Sulphur. 

 Martial Pyrites, 



29. Thefe are ftony concretions of ful- 

 phur, clay, and calx of iron, fo hard as to 

 give fire with fteel. There are two prin- 

 cipal varieties of them. 



I. VARIETY. 



Pale yellow Pyrites. 



30. This has been already defcribed among 

 the ores of alum, 



II. VARIETY. 



Brown or reddifo brown Pyrites. Miner a fern 

 be pat ic QI Waffer kiefs. 



31. It is generally of a fpherical ihape, or 

 cryftalized in cubic, rhomboidal, or other po- 

 lyhedral forms, and is devoid of metallic 

 luftre ; it difficultly gives fire with fteel, and 

 contains very little fulphur, but much more 



iron 



