90 



100.21 



• Our sericite differs from the normal t^^pe in containing an excess 

 of Si 0.,, but less of Al.,03 and KoO. 



Boricky's sample also contained pi^^tassium, and a small qiiantiry 

 of calcimn and sodium. 



The flakes of sericite show a minutely folded texture; their appear- 

 ance closely resembles wrinkled band)oo-paper, and this structure is 

 very characteristic of this mineral. The sericite is commonly heaped 

 aroimd the periphery of felspars and epidote after the manner of a 

 fringe, as if it were produced from both minerals. ( %. 3, PI. II). 



A greenish-yellow epidote occurs in irregular plates, traversed as 

 usual by numerous, approximately parallel, curved fissures in the 

 direction of the vertical axis. As these transversal rents are probably 

 the contraction-fissures, tlieir course is at rio-ht ano-jes to the cleavao:e- 

 planes (oP.oo Poo ) of this mineral. The size varies from Yi,-1 centim., 

 and seldom sinks into microscopic dimensions ; so that the mineral is 

 macroscopically discernible as yell<nv spots on the cleaved [)lane of 

 the rocks. 



A characteristic feature of the epidote in this rock is the abun- 

 dance of microscopic interpositions of iron-glance, and rutile-needles. 

 The former is sometimes heaped together in such enormous quantity 

 within the crystal as to give to the epidote almost an opaque appear- 

 ance, while the periphery is comparatively free from it. Crystals are 

 torn asunder into vai'ious parts, each part being joined to the other 



