no 



has found that the acute bisectrix forms an angle of 8^/2° 

 with the vertical axis. Now, 1 think, that the catapleiite from 

 the two places must necessarily be supposed to belong to the 

 same crystalline form, and so there can scarcely be any doubt 

 that also the Greenland mineral must be monoclinic. This 

 mineral, however, is not so well developed with regard to its 

 crystallographic properties, as to render a more particular ex- 

 ajnination of its crystalline form possible. In the following I 

 shall therefore only point out a few physical and optical pro- 

 perties of the Greenland catapleiite, as in several respects it 

 seems to present interesting facts. 



With regard, in the first place, to the temperature at 

 which the transformation from the monoclinic form to the 

 hexagonal one takes place, the most essential facts have already 

 been given by Flink, who states that, as to type 1, the lamellae 

 disappear at 120°, as to type 2 they have not completely dis- 

 appeared at 200°, while, for type 3, the transformation takes 

 place at ca, 10 — 20°; a part of a crystal was found, however, 

 which at common temperature was still completely uniaxial (see 

 M. 0. G. 24, Pl.V, flg. 10). To these results I can add nothing 

 essentially new; for type I I have found that the transformation 

 begins at 110°, and is completed at 130°; in type 2 the trans- 

 formation begins at 160°, but is only completed at 230°. Type 

 3 is somewhat varying; some crystals are transformed at 10 — 

 20°, as mentioned by Flink; most of them, however, would 

 seem to need a somewhat greater heating, as the transformation 

 does not begin until at ca. 30°, and finishes at ca. 40°. TJie 

 uniaxial part figured by Flink is seen, by a cooling down to 

 ca. 8°, to be penetrated by lamellæ like the other parts. 



The crystals of type 4 are rather peculiar with regard to 

 their optical properties; some of them are, at the common 

 temperature, distinctly lamellated, others are completely uni- 

 axial, and all transitions between both forms are found, the 

 lamellae being sometimes exceedingly indistinct, sometimes only 



