100 B. KÜTÖ 



such 118 green mica, hydro-mica, sericite, green biotite, chloritoid, 

 phyllitic element, etc. 



The tour mal i ne forms a very characteristic C(3mi)onent ç,i the 

 spotted black schist, especially as regards its quantity and the per- 

 fection of its forms. The crystals are slender, being bounded by 

 deutero})rism (x Pa) and protoprism (oo K), and terminate in an 

 acute rhomboliedr(3n ( — 2R) at one end, and an obtuse at the other 

 (+R); the basal pinacoid not yet observed; but one pole often 

 broken ; transversal fissures rai'e ; cijal)' particles often foiujd as 

 interpositions. The acute pole rhondjohedron ( — :2[J) is, as a rule, 

 nnsymmetrically developed, while the opposite obtuse end is bounded 

 by a rhombohedral face ( + K) well finished and very regular. And it 

 is a very remarkable fact that the aiitihxjous ( + ) acute pole bounded 

 by — 2R is aUva[is dequtj coloured; while the analogous (— ) obtuse 

 pole (+R) i« of a lighter shade (fig. 8, Fl. II). This difference in the 

 tino-e of colour should in some way be connected vvitli its pyroelec- 

 tric properties, which, as Hauy long ago pointed out, have some 

 close connection with the very characteristic hemimorphism of the 

 tourmaline- crystal . 



The vicinal section (fig. 0, b, VI. U.) of the base of our tourmahne 

 presents some notew(jrthy features which may here be briefly noticed. 

 Some basal sections show a nucleus which is marked off clearly by a 

 tine contour, and also by the lighter colour of the centre, while others 

 ( fig. 9, a, PL II.) show an imperfect external shell with half-covered 

 internal parts. Examples of the former are often/ fcund in various 

 plagioclases known as isomorphic shells (isomorphische Schichtung); 

 while in the latter Ave have an example of a parallel growth of indi- 

 viduals of the same mineral species, the well-known vertical stri[)es of 

 tourmaline-columns being due greatly to this special growth. Bearing 

 in mind the facts stated above, we are now forced to believe that the 



