109 



have always, however, an especially marked maximum, the 

 distance of which from c(000l} has been measured to 25° 17' 

 (25° 4' — 25° 37'), that is to say, about the same angle as that 

 found by Flink in type 1, which differs to a so remarkably 

 high degree from the calculated angle, which, according to 

 FlinkM, for the Greenland catapleiite is 27° 28'. It is, however, 

 scarcely possible to determine the face in any other way. 



The crystals are transparent, without inclosed bodies, of 

 a slightly brownish colour. 



Although the form of these crystals is not very different 

 from Flink's type 1, they appear nevertheless to be so different 

 from this type in their optical relations, that they must be 

 regarded as a special type, which, in accordance with the three 

 types described by Flink, I shall designate as type 4. 



General remarks on the physical and optical 

 properties of the Greenland catapleiite. 



Almost all catapleiite, as is well known, is optically un- 

 homogeneous by common temperature, being in sections after 

 the base composed of a great number of generally quite thin, 

 optically biaxial lamellae; in other directions, as shown by 

 Brøgger^), a few thin lamellae may be found; in the Greenland 

 material, however, I have not observed such lamellae. 



The crystalline form to which the single individuals belong 

 has been found by Brøgger ^) to be monoclinic with the elements: 

 а\Ъ:с = 1-7.329: 1 : 1-3618 

 ß = 89°48A'. 



Flink ^) arrives at the conclusion that the catapleiite is 

 rhombic, especially because the acute bisectrix has been found 

 to be perpendicular to the base; Brøgger, on the other hand, 



1) Medd. om Grønl. 24, p. 100. 

 -') Zeitschr. f. Kryst. 16, p. 442. 

 3) 1. с p. 437. 

 *) M. 0. G. 14, p. 97. 



