HOVEY, THE FOYER METEORITES 17 



taining some iron, which occurs in all the siderolites and most of the 

 aerolites, sometimes comprising a considerable portion of their mass. 

 It is a dark yellowish-green to black, glassv mineral usually occurring as 

 rounded or angular grains, but sometimes as crystals. It is prominent 

 in a slice of Brenham in the Foyer collection, where it forms glassy 

 grains in a mesh of nickel -iron. Olivine is the gem, peridot. 



The minerals belonging to the group known as orthorhombic py- 

 roxenes are next to olivine in point of abundance. Chemical analyses 

 show that all gradations are present from the colorless enstatite to the 

 almost black hypersthene members of the group. The monoclinic 

 pyroxenes, which are important constituents of terrestrial igneous rocks, 

 are represented in meteorites by only two forms, an iron-alumina pyrox- 

 ene like common augite and one nearly free from iron and without 

 alumina which is to be compared with diopside. The augite-like mineral 

 is brown to green in color and occurs usually in grains or splinters rarely 

 in crystals. It has been found in many meteorites, but diopside has 

 been identified only once with certainty. 



The great feldspar series has been identified in meteorites in four 

 of its forms, namely: anorthite, albite, oligoclase and labradorite. 

 Of these, anorthite has been found forming a large part (35 per cent.) 

 of some meteorites and measurable crystals have been obtained, but in 

 most cases where feldspar occurs in a meteorite, it has been possible to 

 go no farther than to identify it as belonging to the plagioclase section 

 of the mineral group. 



Maskelynite is a transparent, colorless, glassy mineral. In chemical 

 composition it is related to the terrestrial species leucite, but it is a dis- 

 tinct form and thus far is known only from meteorites. It is not known 

 to occur in any of the meteorites displayed in the Foyer. 



Accessory Constituents. 



Schreibersite is a phosphide of iron, nickel and cobalt which is 

 probably peculiar to meteorites. It is tin-white in color, changing to 

 bronze-yellow or steel gray on exposure to the air. In structure it is 

 granular, flaky, crystalline or needle-like. Next to nickel-iron schrei- 

 bersite is the most generally disseminated constituent of siderites and 

 forms some of the shining lines to be seen on etched sections. 



Carbon occurs in at least three forms in meteorites, as the diamond, 



