226 



University of California. 



[Vol. 3. 



on the albite law. The symmetrical extinction angles of these 

 albite lamellae do not exceed the low values characteristic of 

 oligoelase. The specific gravity as determined on three selected 

 fragments was found with the Westphal balance to be 2.630, 

 2.634 and 2.636, the average being 2.633. An analysis of the 

 feldspar, which was kindly made by Mr. J. Newfield, of the 

 Chemical Department of the University of California, gave the 

 following results: 



99.51 



This calculated to a water free basis gives the following 

 molecular ratios : 



These ratios correspond to those of an oligoelase of the formula 

 Ab.i Ano with 2.7 per cent, of Si02 to spare. 



The Corn ml ii in . — The corundum is in crystals ranging in size 

 from a few millimeters to over five centimeters in length. These 

 are of a pale violet blue color. In most cases they are imperfectly 

 formed but many were observed with well defined crystal forms, 

 showing sharply hexagonal cross-sections. The faces of these 

 crystals are rough and do not lend themselves to measurement 

 with the reflecting goniometer. There is apparently but one 

 habit represented and this is due to an acute rhombohedron 

 without prismatic faces. The angle between two of these rhom- 

 bohedra, measured over the basal edge with a contact goniometer, 

 was found to be 164° and between the same two faces over the 

 polar edge 120°. These values agree with those given for the 

 form (8.8.16.3). There is occasionally observed a parting in 

 these crystals parallel to the base. The specific gravity of the 

 corundum varies from 3.9 to 4.2 with an average value of about 



Si0 2 



A1 2 3 



CaO 



Na 2 



H 2 



61.3(3 

 22.97 

 5.38 

 8.08 

 1.72 



1.045 

 .230 

 .098 

 .134 



4.0. 



