So Elements of Mineralogy. 



Bergm. 476, yet do not become magnetic. 

 Rinman, , 89. The yellow, when heated 9 

 become firft red, and in a ftrong heat, brown 

 or black. Calamita bianca of the Italians is a 

 white bole, ftriated like afbeftos. Ferber* 

 It ally ^ 122. Terra figillata rubra contains 

 calcareous Earth, and becomes magnetic after 

 torrefadtion. Rinman^ 189, 



Of Volcanic Origin. 

 Pouzzolana. 



This is of a grey, brown, yellowifh, or 

 blackifh colour, loofe, granular, or dully, 

 and rough, porous and fpungy, refembling a 

 clay hardened in fire and then reduced to a 

 grofs powder. It contains, mixed with it, 

 various heterogenous fubftances : its fpecific 

 gravity is from 2,5 to 2,8, and it is in fome 

 degree magnetic.* it fcarcely efftrvefces with 

 acids, though partially ioluble in them : it 

 melts eafily perfe : but its moft diftinguifhing 

 property is, that it hardens very fuddenly 

 when mixed with ^ of its weight of lime and 

 water, and forms a cement, which is more 

 durable in water than any other. According 

 to Mr. Bergman's analytic, loo parts of it 

 contain from 55 to 60 of filiceous Earth, 19 

 or 20 of argillaceous, 5 or 6 of calcareous, 

 and from 15 to 20 of iron. 3 Bergm. 193. 

 It is evidently a martial argillaceous marl 



that 



