1871.] 



Mineral Constituents of Meteorites. 



267 



Meissen to Breitenbach, the author proceeds to describe the individual 

 minerals which constitute the mass of the Siderolite. 



These are : first, a bronzite with the formula (Mg* Fe^ ) Si 3 , or- 

 thorhombic in its crystalline form. The crystallography of the mineral 

 was investigated by Dr. Viktor von Lang at the British Museum, and has 

 been published in Pogg. Annalen, vol. cxxxix. p. 315. Secondly, a mineral 

 composed of silica, having the specific gravity of quartz after fusion, and 

 crystallized in the orthorhombic system. 



Since his preliminary notice was published, the crystallography of this 

 substance has been carefully studied by the author, and the details are 

 given in the memoir. 



The elements of the crystal are 



a : b : c : = 1*7437 : 1 : 3*3120. 

 The angles are : — 



1 00:1 1 = 27° 46' 

 1 00:1 1 = 60° 10' 

 110:101 = 63° 19' 



The optic axes lie in a plane parallel to the plane 10; the first mean 

 line being the normal to the plane 10 0. 



They are widely separated, presenting in air an apparent angle of 

 about 107°. 



There can thus be no question that this mineral is orthorhombic ; and 

 if the tridymite of Vom Rath is, as that distinguished crystallographer 

 asserts it to be, hexagonal in its symmetry, the mineral in the Breitenbach 

 meteorite will be a trimorphic form of silica. Such a result obtained 

 from the investigation of a meteorite is one of no small interest. 



The nickeliferous iron, the chief constituent of the Siderolite, proved on 

 analysis to be an alloy of the formula Fe 10 Ni, and contained a trace of 

 copper. In addition to the two siliceous minerals, the iron encloses 

 occasional crystals of chromite in well-developed octahedra, an iron sulphide, 

 probably troilite, and a small amount of Schreibersite. 



The author then proceeds to detail the results obtained from the analysis 

 of the Shalka meteorite. In 1860, Haidinger, in his paper on this 

 meteorite (Sitzber. d. k. Akad. Wiss. "Wien, vol. xli. p. 251), held the entire 

 stone to be made up of a mineral, which he termed Piddingtonite, and 

 which, according to Von Hawr's analysis, might be a compound of bisili- 

 cate and trisilicate of iron and magnesium. This latter acid silicate, 

 however, which has long haunted the mineralogy of meteorites, no more 

 forms a constituent of this meteorite than does the other acid silicate 

 Shepardite, as Dr. Laurence Smith has shown, enter into the composition 

 of the Bishopville meteorite. 



The view held by Haidinger, that this meteorite, though apparently 

 made up of two silicates, a grey and a mottled variety, was nevertheless 



