602 Br. Walter Flight — History of Meteorites. 



and occurs in unusually well-developed crystals, which have been 

 found by von Lang to agree in all respects with the olivine from 

 basalt ; the following measurements were made : 



Calculated. 

 100, 110 = 65° 2' 65° 2' 



110, 110 = 49 49 49 57 



100, 210 = About 46 30 47 2 



100, 310 = 35 30 35 36 



100, 210 . = 41 40 27 



The fissures of many of the crystals are filled with a black 

 mineral of a dendritic form ; this is assumed to be chromite and 

 is believed to be a secondary formation. This silicate has the specific 

 gravity 8-307 and the following composition : 



Silicic acid 40 - 14 



Chromium oxide 0-60 



Iron protoxide 13-55 



Magnesia 46-01 



100-30 

 These numbers differ only to a slight extent from those of an olivine 

 in which the two compounds Mg 2 Si0 4 and Fe 2 Si0 4 are in the ratio 

 of 82 : 18. 



The bronzite occurs in grains and imperfect crystals, on any of 

 which faces of more than one zone are rarely recognisable. On one 

 crystal von Lang determined the following angles : 



Calculated. 



100, 320 = About 34° 50' 34° 30' 



100, 110 = 45 56 45 52 



100, 230 = 57 15 57 6 



100, 130 = About 71 56 72 5 



while a second gave the following numbers : 



Calculated. 

 110, 010 = 44° 6' 44° 8' 



010, 110 = About 44 44 8 



The calculated angles are based on observations made on the 

 bronzite of the Breitenbach siderolite (see page 549). The plane of 

 the optic axes is parallel to the zone [110, 010] and the mean line 

 perpendicular to 010 has a negative optical character. The specific 

 gravity of this mineral is 3-813 and the composition : 



Silicic acid 55-35 



Alumina 0-60 



Iron protoxide 12-13 



Magnesia 32-85 



Lime 0-58 



101-51 

 which corresponds, in point of constitution, with a bronzite in which 

 the isomorphous compounds Mg Si0 3 and Fe Si0 3 are present in the 

 ratio 78 : 22. 



When a microscopic section of this mineral is examined it is found 

 to enclose three substances: 1) colourless chondra of a doubly re- 

 fracting mineral, which the crossed Nicols show to be twinned, and 

 which is probably a felspar ; 2) small round black particles, usually 

 lying in groups, and believed to be chromite ; and 3) fine hair-like 



