132 WARREN. 



010 sections. The microeline is quite fresh; the albite contains fre- 

 quently minute vesicles. A few muscovite flakes were noted. 

 The extinction angles are: — 



Microeline — on 001 .... 18° 



— " 010.... 4.5° 



Albite — " 001.... 3.7° 



— " 010.... 18° 



Specimen No. 3, from Thirteen Island Mine, Bedford Township, 

 Frontinac Co., Ontario, Canada.— The color is a light flesh red; 

 perthitic structure can be seen only imperfectly although its presence 

 is suggested by a lining seen most clearly on the 010 cleavage. The 

 feldspar is, therefore, essentially a microperthite. The albite lamellae 

 are very small, rarely exceeding 0.1 mm. in width and averaging con- 

 siderably less. There is, however, a fairly sharp distinction in order 

 of magnitude between the larger bands and the series of very minute 

 lamellae which lie between them. The smaller series have the appear- 

 ance of being more strongly segregated midway between the larger 

 ones. The latter are quite irregular in direction and they commonly 

 break up into several veinlets of smaller bands, or even into a series 

 of lenticular bodies, which may coalesce farther on into a single band 

 again. In some areas the structure is extremely complex and great 

 care and patience had to be exercised in order to obtain accurate 

 measurements. The microeline in the proximity of the albite bands 

 frequently contains numerous minute specks or vesicles, some of 

 ferruginous character. (Hence the red color of specimen.) 



The twinning in the microeline, though very fine, is exceedingly 

 perfect and beautiful; that in the albite is also very fine so that exact 

 extinction measurements are difficult to make. Furthermore the 

 extinction positions in the microeline in 010 sections are variable. 

 This is probably due to a slight deorientation of the feldspar and is 

 doubtless connected with the slight variations in the level of the cleav- 

 age sui'faces, particularly noticeable in this feldspar. The extinction 

 angles are: — ■ 



Microeline — on 001 .... 17° 



— " 010.... 5° to 10°. 



Albite — " 001 .... 4° to 5° (average of several 



measurements made on broader twin lamellae). 



— on 010.. ..17.8° 



