THE CONSTITUENTS OF METEORITES 399 



pyroxenes of meteorites are thus seen to be entirely compar- 

 able to the terrestrial minerals of the same name. 



Monoclinic pyroxenes. — Two kinds of monoclinic pyroxenes 

 have been identified in meteorites, the first bearing iron and 

 alumina, the second free from alumina and nearly free from 

 iron. The first may be considered similar to terrestrial augite, 

 the second to terrestrial diopside. Augite has been identified 

 in many meteorites, diopside positively only in one. Crystals 

 of meteoritic augite have been measured goniometrically and 

 eight forms similar to those of terrestrial augite found. As a 

 rule, however, the augite occurs as grains or splinters. It varies 

 from brown to green in color, in some meteorites is pleochroic 

 in thin section in others not at all. Parting parallel to the base, 

 owing to repeated twinning, is common and characteristic. It 

 is sometimes regularly intergrown with orthorhombic pyroxene. 

 Inclusions of glass and black dust are common. Pyroxene 

 resembling diopside was identified by Maskelyne in the Bustee 

 meteorite. It occurred in grains and splinters and was of a gra}^ 

 to violet color. A few goniometric measurements were possible. 

 Analysis showed the composition to be that of a calcium- 

 magnesium pyroxene. Crystals and grains from a few other 

 meteorites may perhaps be referred to diopside but the determi- 

 nation is not certain. 



Plagioclase . — Of the minerals of the feldspar group, anorthite 

 may be mentioned as forming an essential constituent of the 

 classes of stone meteorites known as eukrites and howardites 

 and as occurring in others. It forms according to Rammelsberg 

 about 35 per cent, of the stones of Juvinas and Stannern. Of 

 the other members of the plagioclase series, albite, oligoclase 

 and labradorite have been reported in single meteorites, but in 

 most cases where plagioclase has been found the species has not 

 been determined. Orthoclase has not yet been identified in any 

 meteorite. Crystals of anthortite from the Jonzac meteorite 

 reach a length of i'^'". From the druses of the Juvinas meteor- 

 ite anorthite crystals were obtained which served for goniomet- 

 ric measurement, eight forms being thus identified. Some 



