SALMON — ON ROCKS. 237 



also found to correspond with the leading physical varieties of 

 the mineral. 



1 



A 



B C 



D 



E 



Monoxide bases . . . , < 



1 



1 1 1 



1 



1 



Sesqui-oxide bases .... 



3 



4 6 



9 



12 



Silicic and Boracic acid . , 



5 



6 ! - 8 



12 



15 



O.Q. (B) .... 



0.8 



0.833 0.875 



0.833 



0.866 



A. Yellow and brown Tourmaline, with little Fe (2) and the 

 largest quantity of Mg (11) ; together ^vith B (9), Fl (2), ISTa (2), 

 Ca (1), and some K. 



B. Black Tourmaline, containing a mean proportion of Fe (7) and 

 Mg (8) ; together with B (8), Fl (2), Na (2), Oa (1), and some K- 



C. Blackest, with largest proportion of Iron, Fe (8), Fe (6), and 

 least of Mg (2) ; together with "B (8), Fl (2), Na (1), with some 

 Oa and K. 



D. Violet, blue, green, generally containing some Li, Fe (5), and 

 Mn (3) ; together with B (7),'Na (2), Fl (2), Mg. (1), with some Ca 

 and K. 



E. Red Tourmaline, with Li(l) but no Iron ; together with B (8), 

 Fl (2.5), Na (2), K (1), and Mg (1). 



The whole of Rammelsberg's analyses, classed on these five 

 divisions, are to be found in Brooke and Miller's edition of " Phillips's 

 Mineralogy." Schorl^ the black variety, is the most abundant. 



Hermann divides ail the varieties of Tourmaline into three species, 

 with the following formulse, the R bases being placed in the order of 

 quantity, and the Al being assumed to be replacable by ^'e, 



1. Schorl . . (Fe, Mg, Li, Na) B+ "ll "Si. O.Q. = 1.0 



2. Achroite . 2 (Na, Li, %, Mn) B + 3 IP Sil O.Q. = .9090 



3. Rubellite 2 (Na, Li, Mn, Mg) ^BV 3 ll^ Bi". O.Q. = 1.0 

 assuming the Boracic acid to be a binoxide. 



We find by pseudomorphs that Tourmaline is convertible into Mica, 

 Chlorite, and Steatite. In these alterations Al is always separated, 

 until in Steatite, the final product of alteration, it disappears. 

 Besides this, the decomposition takes place in two different directions : 

 in the conversion into Mica, alcalies are introduced ; while in the 



VOL. II. 



