118 PHYSIOCRAPltY. 



mon colour. Translucent on the edges, hya- 

 cinth-red or wine-yellow. 

 Hardness = 5-5. Sp. Gr. = 2-875. 



It consists, according to Dr WALCHNER, of 



Silica 31-634. 



Protoxide of Iron 29*7 1 1- 



Magnesia 32-403. 



Alumina 2-211. 



Oxide of Manganese 0-480. 



Potash 2-788. 



Chrome a trace. 



Before the blowpipe it becomes first black and magnetic, 

 and then melts into a black magnetic globule. It was found 

 imbedded in a brown basaltic amygdaloid in the Kaiser- 

 stuhl near Sasbach in Brisgaw, accompanied by paratomous 

 Augite-spar, &c. The mixture of iron-slags and of pris- 

 matic Chrysolite are very analogous to that of Hyaloside- 

 rite, and the latter is therefore considered by MITSCIIER- 

 LICH as a peridot, in the chemical sense of the word, 

 meaning a silicate of protoxide of iron, or of the isomor- 

 phous bases of protoxide of manganese, magnesia, &c. 

 having the same prismatic form. Hardness and specific 

 gravity are given lower than would be necessary for unit- 

 ing Hyalosiderite with the natural-historical species of pris- 

 matic Chrysolite. 



HYDRATE OF MAGNESIA. 



MICA. 



Native Hydrate of Magnesia. BREWSTER. Trans. Roy. 

 Soc. Edin. Vol. IX. p. 239. Native Magnesia. JAM. 

 Syst. Vol. II. p. 279. Man. p. 468. Hydrate of Mag- 

 nesia. PHILL. p. 95. 



Rhombohedral. Low six-sided prisms, rare.* Mas- 



* A fine specimen of this variety is in the possession of Dr 

 ANDERSON of Leith. H. 



