STRUCTURE OF METEORITES MERRILL. 



181 



several of the known instances prevail to the almost entire exclusion 

 of other constituents. The more common varieties, as will be noted 

 from the accompanying table, are enstatite and bronzite, though 

 hypersthene has been reported in the stone from Shalka. The min- 

 eral, however, is not as pleochroic as is its terrestrial counterpart. 

 Many of these have been identified crystallographically, and agree in 

 form and faces with those of terrestrial rock, although the crystal 

 outlines and cleavages are, as a rule, very poorly developed. 



Analyses of meteoric orthorhombic pyroxenes. 



In addition to these terrestrial forms there are others radically 

 different. Especially characteristic are eccentric and radiated forms 

 some of which are shown in the photomicrographs (pis. 8 and 9). 



The monoclinic pyroxenes are less abundant than the ortho- 

 rhombic, and but for inclined extinctions of clinopinacoidal sections 

 are often difficult to distinguish. The most striking peculiarity of this 

 form is a decided tendency to polysynthetic twinning. This mani- 

 fests itself in fine, parallel striations traversing the section and has 

 caused the mineral on casual inspection to be mistaken for a plagio- 

 clase feldspar. Most of the analyses given in the literature are of 

 materials separated from other constituents by the use of acids, but 

 I have here limited myself to two analyses of such as have been 

 separated mechanically. 



Constituents. 



Source. 



I. 

 Dusti. 



II. 

 Shergotty. 



Silica (Si0 3 ) , 



Alumina (AI2O) 



Ferric oxide (Fe 2 8 ) . 

 Ferrous oxide (FeO) . 



Magnesia (MgO) 



Lime(CaO) 



Soda(Na 2 0) 



55.49 



52.34 

 .25 



.55 



23.33 



19.98 



.55 



23.19 

 14.29 

 10.49 



99.90 



Specific gravity. 



100.56 

 3.466 



65133°— sm 1917- 



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