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BULLETIN 94, UNITED STATES NATIONAL MUSEUM. 



2. Monoclinic pyroxenes: diopside and diallage. These forms of 

 pyroxene are, on the whole, less common in meteorites than are the 

 orthorhombic forms, though it is possible that they are in reality 

 more abundant than is generally supposed, their close resemblance 

 in all but optical properties (which, owing to the small size and 

 poorly developed crystallization, can not always be determined) ren- 

 dering a sure discrimination somewhat difficult. The composition is, 

 presumably, fully as variable as that of the enstatites, but few actual 

 analyses of pure materials have been made, owing to the difficulty in 

 separating them from the associated minerals. Of the following 

 analyses No. I is by Maskelyne ^ and II by Tschermak.^ 



As with other silicate constituents, the monoclinic pyroxenes are 

 but poorly developed crystallographically, are nearly colorless., non- 

 pleochroic, and with extinction angles rarely going beyond 25°. 

 They are often intergrown with enstatites, and still more commonly 

 occur in twinned forms grouped in chondrules. 



8clireU)ersite. — This mineral, first described and named by Haidin- 

 ger in 1847 as a constituent of the Magura iron, and since found as 

 one of the commonest of the accessory meteoric constituents, is a 

 phosphide of nickel, iron, and cobalt, coijesponding to the formula 

 (FeNiCo)3P. It occurs commonly in thin angular plates of a tin- 

 white color, sometimes lying parallel with the taenite-kamacite 

 plates, sometimes in angular, jagged masses as in the Tombigbee 

 iron (see specimen No. 252, also pi. 36), and in dendritic forms as 

 in the iron of Arispe (see specimen No. 299 and pi. 33, fig. 2). In 

 the pallasites it may occur in thin plates lying between the olivines 

 and metallic mesh. It is magnetic, and difficultly soluble, the last 

 feature rendering its separation from the other constituents a matter 



1 Philos. Trans. Roy. Soc. London, vol. 160, 1870, p. 202. 

 2Sitz. Akad. Wiss. Wien, vol. 65, 1872, p. 126. 



