Ss en: ee ee a II E 
1894.] ~ Mineralogy. 701 
forms R,—1R, 1R,—2R, œ R2, œR, and oR. The axial ratio is a:c 
—1:2.1072. The mineral has good cleavage parallel to the base and 
one varying from very good to poor runs parallel to the second order 
prism. The color is usually cherry to garnet red. The crystals are 
specially interesting because of a marked zonal structure and of a 
division into sectors having differences in double refraction. Some of 
these sectors have positive and others negative double refraction. Like 
the eudialite from Magnet Cove the crystals are optically anomalous, 
sometimes having biaxial character with optical angle as large as 15°. 
On heating the sections of the crystals to a temperature at which 
boracite had become isotropic, all the sectors of the field seemed to 
give negative double refraction. Ramsay finds evidence that the differ- 
ent zones of the mineral possess different specific gravities as well as 
different double refraction, and he considers this to be due to isomor- 
phous growth together of eudialite and eucolite. He shows that as 
regards axial ratio, specific gravity, double refraction and optical char- 
acter, there is a gradation from the eucolite of Aró through the eudia- 
lites of Umptek and Kangerdluarsuk to the eudialite of Magnet 
Cove. 
