42 Y. KIKUCHI 



C(UT08ion-fignrps. — Souie experiments liave heen tried in regard 

 to tlie clinracter of corrosion-figures (Aetzfiguren) on cleavage-faces. 

 Clear cleavage-pieces were selected, and acted npon hy dilute fluoric 

 acid, and by hydrochloric acid. In some natural cleavage-faces which 

 have been long exposed to the action of atmospheric agencies, corro- 

 sion-fignres are found similar in character to those produced artifi- 

 cially. These figures are most distinct under a magnifying power of 

 200-300 diameters. 



On the face 7^=001 triangular impressions are formed (fig. 13). 

 These triangles are asymmetric, rounded on one side, while the other 

 sides are nearly straight; the angle formed by the latter being directed 

 backward, as observed by Wiik.* 



On the face 7^'= 001, the figures are reversed as shown in fig. 

 14, the angle formed by the straight sides being pointed forward. On 

 observing the difterent figures, we find some of them formed of dif- 

 ferent faces apparently of îi hemidome and quarter-pyramids (fig. 13 a, 

 /), c), different stages of such development being seen. The figures 

 produced by hydrochloric acid on these faces are smaller and the angle 

 formed by the straight sides more acute than those produced by fluoric 

 acid. Wiik considers the two straight sides as being formed of 

 /(Go.P;3)and2;(oo;P3). 



On Ihe face ilf=010 are produced the elliptical figures observed 

 by AViik. The one end of the longer axis of the ellipse is pointed, and 

 directed upward and backward (fig. o). The direction of the hmger 

 axis is inclined in the same sense as that of the Pericline-lamella?, 

 makino- an ano-je of nearly ^^° with the edge of P : il/. 



4'he figures which are produced on the face M' = 010 are of the 

 same form, but reversed iu position, as shown in fig. 16, the pointed 

 end of the figure ])eing directed dc^vnward and forward, and arranged 

 in the same direction as those on M. 



* R'?ferat in Zeitsclift-. f. Krystallographie. Bd. 7. p. 188. 



