173 STUDIES FOR STUDENTS 



chondri already mentioned, which are granular in part and in 

 part fibrous, are usually made up of the two minerals chrysolite 

 and bronzite. These minerals may be present in about equal 

 quantity or either may be in excess. Usually the bronzite together 

 with glass appears to occupy the intervening spaces between the 

 chrysolite grains, indicating that it is of later formation. Augite 

 chondri are not common but occasionally occur. They often 

 show a structure which indicates repeated twinning. The min- 

 eral may appear also in the form of grains, usually of a green 

 color. These grains can be distinguished from chrysolite by 

 their behavior in polarized light. Chondri containing plagio- 

 clase in any large quantity are also rare but have been observed 

 by Tschermak in the stone of Dhurmsala. The plagioclase 

 alternates in bands with chrysolite and is in excess. Chondri 

 also occur which are composed almost exclusively of glass, the 

 only indication of the presence of other minerals being in the 

 presence of forked microlites which may be referred to bronzite. 

 Occasionally these microlites are of a pronounced star-like form. 

 Chondri, or at least rounded spheres of nickel-iron, occur in 

 some meteorites, though they are not common. All gradations 

 occur from chondri which contain grains of nickel-iron to com- 

 plete spheres of nickel-iron. In the stone of Renazzo such 

 spheres have a covering of brown glass. Some of the spheres 

 or rounded fragments also contain troilite, but troilite of itself 

 never has been seen to form chondri. A more or less complete 

 rim of metal is a characteristic of many chondri. The metal may 

 occur in the form of rounded grains or as a continuous periph- 

 ery. It has been suggested by Daubree that such a rim shows 

 that the chondrus has been subject to the reducing action of 

 hydrogen. Besides the chondri colored black by inclusions of 

 iron and troilite, as previously described, black chondri, which 

 consist chiefly of maskelynite or granular plagioclase, occur in 

 the stones of Alfianello, Chateau Renard and others. These 

 chondri are transparent and colorless about their rim, but in the 

 interior are totally black from inclusions of angular rounded 

 grains, some of which are shown by their brown color to be 



