18S PHYSIOGRAPHY. 



ture rather imperfectly slaty, cross fracture fine 

 earthy. 



Faint glimmering in the principal fracture, dull in 

 the cross fracture. Colour intermediate between 

 greyish- and blueish-black. Retains the colour 

 in the streak, and acquires a higher degree of 

 lustre. Opake. 



Sectile. Soils more or less, and writes. Adheres 

 a little to the tongue, feels fine and rather 

 meagre, and is very soft. Sp. Gr. = 2-114, 

 KIRWAN ; = 2-186, BRISSON. 



Exposed to fire it loses its black colour, and becomes 

 reddish or reddish-grey. Before the blowpipe it yields a 

 white glass, according to LINK. The variety from Bay- 

 reuth has been found by WIEGLEB to consist of 



Silica 64-50. 



Alumina 11-25. 



Oxide of Iron 2'75. 



Carbon 11-00. 



Water 7'50. 



It occurs in rocks of clay-slate, and seems to be very near- 

 ly allied to clay -slate and alum-slate. The finest and most 

 applicable varieties come from Italy, Spain, and France. 

 It is also found in Bayreuth, in Thuringia, &c. It is used 

 as a drawing material. 



FULLER'S EARTH. 



Fuller's Earth. JAM. Syst. Vol. II. p. 300. Man. p. 442. 

 Fuller's Earth. PHILL. p. 52. 



Massive. Composition impalpable. Fracture un- 

 even, splintery, earthy : in the great sometimes 

 imperfectly and flat conchoidal, or even slaty. 



