352 PHYSIOGRAPHY. CLASS II. 



2. Among the various kinds of rhombohedral Tourma- 

 line, analysed by chemists, we notice the following : 



Red Tourmaline Green Tourmaline Blue Tourmaline Black Tourmaline 

 from Siberia. from Brazil. from V tori. from Eubenstock. 



Silica 42-00 40-00 40-30 36-75. 



Alumina 40-00 39-00 40-50 34-50. 



Soda 10-00 0-00 0-00 0-00. 



Lithia 0-00 0-00 4-30 0-00. 



Potash 0-00 0-00 0-00 C-00. 



Lime 0-00 3-84 0-00 0-00. 



Oxide of Iron 0-00 12-50 4-85 21-00. 



Oxide Of Man- with Manganese. 



ganese 7'00 2-00 1-50 0-00. 



Magnesia with a mtie iron 0-00 0-00 0-25. 



Water 0-00 0-00 3-60 0-00. 



Boracic Acid 0-00 0-00 1-10 0-00. 



VAUQUELIN. VAUQUELIN. ARFVEDSON. KI.APR. 

 GRUNER discovered, in a variety from Greenland, 9 per 

 cent, of boracic acid, a substance which has since been 

 found also in several other varieties. Those Avhich contain 

 lithia intumesce before the blowpipe, and assume a slaggy 

 appearance, but do riot melt ; those which contain soda 

 intumesce still more, but likewise do not melt, except 

 on the edges ; those containing lime intumesce very mucb, 

 and melt into a white slag. Rhombohedral Tourmaline 

 assumes by heat opposite kinds of electricity on the opposite 

 apices, which is in connexion with similar phenomena in 

 the crystallisation of the species. 



3. Rhombohedral Tourmaline is frequently met with in 

 rocks, particularly in granite, but without forming a regular 

 ingredient of any, and is found imbedded in them in larger 

 or smaller masses, or crystallised in the drusy cavities, as, for 

 instance, in the topaz rock of Saxony. It occurs in beds 

 with different species of Augite-spar, Garnet, Iron-ore, &c. 

 The red varieties in columnar compositions from Siberia, 

 are described as occurring with rhombohedral Quartz, in 

 veins traversing a fine grained granite. It is also met 

 with in the shape of pebbles in the stream- works, and in 

 the sand of many rivers. 



