SILICA. 279 



here be obtained, but in some cases they will be found so closely associated with each other, 

 that a specimen of ordinary size will frequently exhibit the gradual passage between the most 

 widely difierent varieties. 



MAGNESITE. 



Magncsitc. Cleavehnil, Bcudanl. — Meer.schaum. Wcnur. — Bihyiirous Tersilicate of Magnesia. Thomson. — 

 A variety of the Prismatic Talc IVIica of Jamesmi, and of the Prismatischer Talc-Glimmer of Muh. — Kero- 

 hte. Shcpard. — Kcrohte, and Hydrous Silicate of Magnesia. Dnna, — Marmolite. NuttaU and Bcudant. 



Under the general name of Magnesite, I include several minerals which are essentially 

 composed of silica and magnesia, and none of them containing any notable proportion of the 

 carbonate of magnesia. 



Description. Colour white, greyish, bluish, yellowish or reddish white. It always 

 occurs massive, often tuberous and reniform. More or less earthy, always very tender. The 

 powder is tolerably hard, and it has usually a smooth and unctuous feel. Fracture earthy and 

 conchoidal. Hardness from 2.0 to 3.0. Specific gravity of magnesite from 2.60 to 3.40 

 [Beudant); of meerschaum, from 0.98 to 2. 12. By calcination, it gives out water. It is 

 with great difficulty fused by the blowpipe into a white enamel. It is partially acted on by 

 acids. 



Varieties. Magnesite. Greyish white, with a tint of red. It is soft, has a smooth and 

 unctuous feel, but its powder is pretty hard. 



Meerschaum. Colour snow-white. Fracture passing into flat, conchoidal. Surface smooth ; 

 fine grained. Sometimes it is very soft, and has the appearance of being a deposit from 

 water. 



Composition. Magnesite — Silica 54.00, magnesia 24.00, water 20.00, alumina 1.40 

 {Berthier). 



Meerschaum — Silica 42.00, magnesia 30.50, water 23.00, lime 2.30, alumina with a 

 trace of manganese 2.00 {Thomson). 



Marmolite, from Hoboken, N. J. — Silica 40.00, magnesia 42.00, water 16.45, deuto.xide 

 of iron 0.90 {Vanuxem). 



Kerolite—S'iYica. 37.95, magnesia 18.01, water 31.00, alumina 12.18 {Pfaff). 



Deweylite — Silica 40.00, magnesia 40.00, water 20.00 (Shepard). 



Geological Situation. All the difl'erent varieties of this mineral are found in veins in 

 serpentine, and sometimes in veins of trap. They are very closely allied to serpentine, with 

 which this species ought perhaps to be united. 



localities. 

 Orange County. Near Greenwood furnace, magnesite of a greyish and yellowish white 

 colour, occurs in veins of from a (juarter to half an inch, in serpentine. It is associated with 

 asbestus, but it is not abundant. 



