51 J 



slightly inclined; the extinction is 32 degrees. The extinction of the 

 third lamel is 85 degrees. These observations unmistakable point to 

 a plagioclase very rich in anorthite. 



The hypersthene is strongly pleochroitic from pale green to brown 

 pink and has a double refraction rather strong for an orthorombic 

 pyroxene. The hypersthene often contains freakishly formed grains 

 of magnetite. 



The olivine, as seen under the microscope, is colourless; it has a 

 high double refraction and is always corroded. 



The above mentioned accessory mineral occurs in well-shaped 

 colourless crystals, which are most like to octahedrons, occasionally 

 with pyramids on the planes, forming triakisoctahedrons ; the size 

 of these crystals is minute, in most cases they are thinner than the 

 .section is, about \j, mm. The slide was ditlicult to cut. The crystals 

 are isotropic, they diminisli the colour of polarisation of the host- 

 crystal, but are dark with the host-crystal between crossed nicols. 

 They show a large black border in ordinary light, also when they 

 occur in olivine, owing to their very high refraction. 



In many cases the border is so large that only a cone of light 

 emerges at or near the centre of the grains ; this cone can be followed 

 by moving the tube up and down. The mineral in question occurs 

 both within olivine and anorthite; in the latter it is principally 

 deposited on the planes of zonal structure. Besides the crystals also 

 some irregular grains occur of the same substance, showing the 

 same properties. 



The hypersthene is, remarkable enough, devoid of this mineral 

 or (contains only some occasional grains. 



A fragment of the rock with a flat side was chosen ; under ap- 

 plications of pressure striae could be obtained on topaz and on 

 corundum. Pressure had to be applied, because in preparing the 

 slides it became evident that the grains of the mineral wore easily 

 jerked out; consequently many cavities are to be seen in the slides. 



To resume: the mineral is isotropic, has an octahedral habitus, 

 a very high index of refraction and a hardness exceeding that of 

 corundum, if at least we may assume that tlie striae on these 

 minerals are due to the minute grains; about this however little 

 doubt is possible. From these observations we must conclude that 

 the mineral is diamond; no further experiment being required, which 

 would indeed be very difficult owing to the extreme minuteness of 

 the grains. 



Assuming this to be true, it seems to me, that it throws a wonder- 

 full happy light upon the genesis of lliis mineral. As everywhere 



