Ill 



found in single parts of the crystal. By a heating to ca. 50° 

 all the crystals become completely uniaxial; by a cooling down 

 below the common temperature, on the other hand, no alteration 

 takes place; those which are uniaxial beforehand, remain so 

 just down to ca. -r- 50°; thus it would seem as if these crystals 

 cannot become monoclinic at any temperature; if they could 

 be transformed at still lower temperatures, it might be expected 

 that indications of a beginning transformation would already 

 appear at the -f- 50°. 



As the transformation of the crystals of types 3 and 4 

 takes place at a temperature so fit for examination, it is a 

 reasonable thing to examine whether it is accompanied by other 

 physical alterations. With regard to the Norwegian catapleiite 

 Brøgger has measured the angles of crystals without being 

 able to find any difference before and after the transformation; 

 the Greenland catapleiite of types 3 and 4 has not so well 

 developed crystalline faces, and especially it has never so large 

 parts belonging to one single monoclinic individual, that such 

 measurements may be made on this mineral with any hope of 

 success. On the other hand I have found that the specific 

 gravity alters perceptibly by the transformation in the inner 

 structure of the crystal. The specific gravity has been deter- 

 mined by means of Thoulet's fluid; the crystal was made to 

 float in the fluid at the temperature that was to be examined; 

 then the specific gravity of the fluid used was determined at 

 common temperature, whereupon the specific gravity of the 

 fluid, at the temperature first used, was calculated by means of 

 the coefficients of expansion stated by Goldschmidt ^). 



By these means the following specific gravities were found: 

 Type 1. Type 3. 



at 17° 2-764 2-751 



- 30° 2-763 2-745 



- 40° 2-764 2-740 



1) N. J. f. Min. Beil.-Bd. 1, p. 230, and PI. 8, fig. 2 



