MODE XIV. SIDEROMAGNESIAtf ROCKS. 127 



the iron-flint, of Werner, is merely a vein-stone, 

 and never appears in the shape of a rock; and 

 generally the silex in siderous substances is lost 

 in the argil. The sidero-caltite and ferri-calcite 

 of Kir wan have little connexion with the present 

 subject, the former being pearl-spar, the latter 

 only embracing a few lime-stones, which contain 

 from 10 to 20 of iron ; but as they easily decom- 

 pose, present no remarkable variety, and are 

 little interesting, it is unnecessary to distinguish 

 them, except as mere diversities of lime-stone. 

 Innumerable marbles are tinged with iron, from 

 which they chiefly derive their colours ; but it 

 would be a too nice and useless distinction to 

 compose an arrangement from this mere acci- 

 dence, which varies in different parts of the 

 same rock. There remain therefore only the 

 magnesian rocks to be specially considered in 

 their conjunction with iron, a metal with which 

 they have often a singular affinity. 



STRUCTURE I. CHLORITE. 



This substance is by Werner divided into four 

 kinds ; chlorite earth, common or compact chlo- 

 rite, foliated chlorite, and chlorite slate. It seems 

 unknown to Wallerius, who published his last 

 edition in 1772 ; but is the green talc of Born, 



