Dr. Walter Flight — History of Meteorites. 559 



More recently this meteorite has been submitted to a very complete 

 investigation by Tschermak. He finds a fractured surface to be 

 distinctly granular ; the grains are of nearly equal magnitude, and 

 among them the eye readily distinguishes two minerals : one of a 

 light brown colour and with very distinct cleavage, the other trans- 

 parent and with a strong vitreous lustre. Further microscopic and 

 chemical examination revealed the presence of three more ingre- 

 dients : a yellow silicate rarely met with and forming grains, 04 mm. 

 across, which exhibit doubly refractive power and appear to crystal- 

 lise in the rhombic system ; they are probably bronzite. Magnetite 

 and magnetic pyrites were likewise present. 



An augitic mineral, the one above alluded to, forms the chief mass 

 of the stone : it has a greyish-brown colour, and exhibits double 

 refraction with slight pleochroism. The cleavage and optical cha- 

 racters suggest its classification with diopside. The analytical re- 

 sults given below, however, show that it cannot be regarded as a 

 member of the augite group : 



Silicic acid ... 

 Alumina 

 Iron protoxide 

 Magnesia 

 Lime 



52-34 

 0-25 

 23-19 

 14-29 

 10-49 



100-56 

 These numbers accord with the formula : 



CaO, 2MgO, 2FeO,.5 Si0 2 . 



A mixture of hypersthene and hedenbergite, the former greatly 

 preponderating, possesses such a composition. Tschermak finds, 

 however, that the silicate cannot be thus constituted, and he con- 

 siders this augitic constituent of the Sherghotty meteorite to be a 

 chemical compound which has not yet been discovered in our terres- 

 trial rocks. 



The second constituent of this stone occurs more sparsely in 

 transparent colourless granules with vitreous lustre and conchoidal 

 fracture ; they proved to be distorted octahedra. " Maskelynite," as 

 Tschermak has named this mineral, does not doubly refract light, 

 and agrees in point of composition with no known cubic mineral, 

 approaching nearest to a labradorite from Labrador examined some 

 time since by Tschermak. The composition of this mineral is : 

 Silicic acid 56-3 



Alumina . 

 Lime 

 Soda 

 Potash , 



25-7 

 11-6 



5-1 

 1-3 



100-0 



In comparing maskelynite with labradorite, or suggesting a pos- 

 sible dimorphism of labradorite, the one form triclinic, the other 

 cubic, the fact must not be lost sight of that labradorite already re- 

 presents a mixture of two silicates, anorthite and albite, which sub- 

 stances, it will have to be assumed, are dimorphous and occur as a 



