OP ARTS AND SCIENCES. 7 



tributed through the meteorite intimately mixed with olivine, although 

 in some cases large crystals of clear green olivine are to be found em- 

 bedded in the ehromite. In several places masses of nearly pure 

 chromite of more than an inch in diameter appear, intersected by the 

 network of iron with its accompanying troilite and schreiberseit, the 

 chromite largely replacing the olivine. This mixture of chromite and 

 olivine appears as a whole perfectly black and opaque, breaking with 

 a subconchoidal fracture, and having a brilliant submetallic lustre. 

 It is strongly attracted by the magnet, and differs most markedly from 

 the dark olivine before described in being perfectly opaque, and the 

 powder is dark brown or black where in the former case it was gray. 



Section of Olivine Crystal showing Chromite. 



A perfect octahedron with an axis of about two millimeters was broken 

 out from one of these masses, but in most cases the chromite took the 

 form of the olivine. The cause of this will be evident by reference to 

 the accompanying figure, which represents a microscopic section of a 

 black perfectly opaque and strongly magnetic lump of this material, 

 the diagram having been drawn from the microscope by means of a 

 camera lucida. It will be seen at once that, instead of its being a 

 homogeneous substance, it proved to be a section of a transparent 

 crystal of olivine which had had all its cleavage cracks well filled with 

 chromite. Under the microscope, the chromite is still perfectly opaque 

 even in such a thin section, and has a noticeably metallic lustre, with 

 no gradual change from dark to light, as was the case in the other 

 variety of dark olivine. 



