56 



grooves, but on account of its smallness it has not been^pos- 

 sible to discover any regularity in the form of these furrows 

 and grooves. The fact is commonly that the middle portion 

 of the lower part of the face adjoining on /"{041}, is quite 

 bright and of the same nature as the other faces, and then, 

 with a rather sharp boundary line upwards and on the sides, 

 it passes into the rough portion. 



The nature of the edges is rather characteristic. While 

 some are quite sharp, others are evenly rounded, but quite 

 smooth. This latter applies to the edges between (lOi) and (101), 

 (101) and (021), (111) and (021), (111) and (041), (111) and (120), 

 (101) and (120), (301) and (120), (301) and (210), (210) and (2l0), 

 so that these rounded edges form continuous lines, connecting 

 the upper edge of the crystal between (101) and (lOT) with the 

 foremost one, between (210) and (2T0). When these edges are 

 placed in the goniometer, it is commonly impossible to discover 

 any single, certain reflex; only in the zone [HI :021] a faint 

 reflex is sometimes seen, the position of which agrees with the 

 face {132}; but as this face is never found with any other 

 development, it has not been included in the list above. 



One more phenomenon has to be mentioned, as it is seen 

 in very many of the crystals of this type, and to a smaller 

 degree also in a few of the others, viz. a very marked and 

 deep furrow, commonly running exactly in the symmetrical plane 

 [ф. (OIO)) of the crystal, through the middle of the faces {lOl} 

 and {ЗО1}, and commonly also through the one of the prismatic 

 faces {210}, where, however, it is less distinct. Where this 

 furrow is present, the right and left sides of the crystal are 

 seen by measuring to be somewhat displaced in relation to 

 each other. This displacing may rise to 1V2°, but is otherwise 

 much varying, which is also the case with the direction of the 

 displacing, so that the displacing cannot, to be sure, be due 

 to a fixed law of twinning. The position of the furrow might 

 seem to indicate that the crystal had been broken in the direc- 



