128 Elements of Mineralogy. 



SPECIES XV. 



Siliceous Earth more or lefs perfefJfy united to 



from 0,46 to 0,83 of its 'weight of Argill* 



from ~ to 4- of Calcareous Earth, and to i 



or L. of femtphlogiflicated Calx of Iron, and 



from T T g- to T T T of Magnefta. 



Schoerl. 



Its diftinguifhing properties are, i ft< either 

 a fparry or femi- vitrified appearance, like an 

 enamel or a flag ; 2 d ' a filamentous or fcaly 

 texture, which diftinguifhes it from garnets ; 

 the filaments either feparate from each other, 

 or conjoined and plated; 3 d * fufibility per fe 

 in a moderate heat ; 4 th ' a fpecific gravity from 

 3, to 3,6, rarely 4,000, and only when load- 

 ed with iron ; 5 th its hardnefs nearly as that 

 of cryftal. 



I. VARIETY. 

 Tranfparent. 



This is always cryftalized in fome poly- 

 gon form : its texture obfcurely fparry : its 

 colour brown, reddifh brown, greenifh or 

 yellowifh brown, or violet : its fpecific gra- 

 vity from 3, ~to 3,6. 



