398 STUDIES FOR STUDENTS 



the presence of a reducing agent. The nickel of the chryso- 

 lite then formed an alloy with the iron of the pyroxene. The 

 siliceous portion of meteorites that is soluble in hydrochloric 

 acid may for the most part be considered chrysolite, since 

 numerous analyses of this portion give results corresponding in 

 composition to this mineral. 



Orthorliombic pyroxenes. — The minerals of this group are next 

 in abundance to chrysolite as a constituent of meteorites. They 

 form an essential part of nearly all stone meteorites and are not 

 lacking in the iron-stone meteorites. At least four meteorites 

 consist of orthorhombic pyroxenes alone. These are the meteor- 

 ite of Bishopville, practically composed of enstatite alone, and 

 those of Manegaon, Ibbenbiihren and Shalka, which consist 

 essentially of hypersthene. The color of the orthorhombic 

 pyroxenes varies from colorless through white to various shades 

 of green. Often the mineral has the typical color of chryso- 

 lite. In thin section the pyroxene is colorless to slightly 

 colored. Its habit is usually prismatic but it may also occur 

 as rounded grains. Crystals with well defined planes have 

 been observed in the Breitenbach, Bustee, Manegaon and other 

 meteorites. A total of thirty-two forms has thus been identi- 

 fied and the axial relations found to correspond with those of 

 terrestrial hypersthene. Prismatic, macrodiagonal and brachy- 

 diagonal cleavages are recognizable. It is especially character- 

 istic of the mineral to form eccentric, radiating, polysomatic 

 chondri, the structure of which has been described in a previous 

 article. 



Numerous chemical analyses of mechanically separated ortho- 

 rhombic pyroxenes have been made. These show all grada- 

 tions between the compositions represented by the formulas 

 MgSiOg (enstatite) (Mg, Fe) SiOg (bronzite) and (Fe, Mg) 

 SiOg (hypersthene) . The portion insoluble in acids, of meteor- 

 ites consisting essentially of nickel-iron, chrysolite and ortho- 

 rhombic pyroxenes, may be considered to be essentially the 

 latter, as shown by numerous analyses which give results cor- 

 responding with the pyroxene formula. The orthorhombic 



