METEORITES OF NORTH AMERICA. 



379 



These areas are at times BO abundant as to form the base in which the other constituents are embedded. They are 

 evidently composed of a single mineral, the optical properties of which are BO ill-defined as to make a satisfactory deter- 

 mination impossible. At times it is quite isotropic, but more commonly it shows a faint double refraction, and in a 

 very few instances the attempt at obtaining an interference figure resulted in a very indistinct dark brush, suggestive 

 of a biaxial mineral. Between crossed nicols, if not always dark, it shows no definite extinction plane, but the dark 

 wave sweeps over the surface much as in an iaotropic mineral in a condition of strain. In a single instance one of these 

 areas adjoined and partially inclosed a minute particle showing the parallel twin bands of a plagioclase feldspar. The 

 mineral is regarded as unquestionably the same as that so common under similar conditions in the meteorite of Alfianello, 

 Italy, and which has been considered by V. Toullon as maekelynite, a conclusion adopted by Tschermak. The present 

 writer also noted its occurrence in the recently described meteoric stone from Coon Butte, Arizona. Compared with 

 terrestrial rocks, it is of interest to note that similar structures and associations of pyroxene or olivine, and what are 

 unquestionably feldspars, are found in peridotites of the wehrlite type, as described by the writer some years ago from 

 the Red Bluff region of Montana. 



In addition to the above is an occasional plate of a colorless silicate likewise of a doubtful nature. The plates are 

 of irregular outline, faintly gray or almost completely colorless, and show very faint, short, sharp cleavage lines, and 

 rarely any inclosures of other minerals which are so conspicuous a feature of the maskelynite. The surface viewed 

 under a high power has a peculiar roughness, in which also it differs from the above. Between crossed nicols it gives 

 weak polarization colors, and is optically biaxial, though good interference figures are not obtainable. The description, 

 given by Tschermak of a mineral referred to as possibly monticellite would apply equally well to this, though the present 

 writer confesses to a considerable feeling of doubt as to its true nature. 



The structure and composition of the stone, as a whole, is comparable with those of Lancon, France, and Bath 

 Furnace, Kentucky (Cia). It will be known as the Rich Mountain meteorite. 



CHEMICAL ANALYSIS BY MR. WIRT TASSIN. 



A very small portion of the meteorite, 5.8 grams in all, was available for analysis. This was treated in the usual 

 way, the native metals (I), sulphur (II), phosphorus (III), soluble and insoluble silicates (IV and V), and the alkalies 

 (VI), each being determined in separate portions. The values obtained are as follows: 



{Fe 7.07 

 Xi 73 

 Co 031 



II. S 1.42 



III. P 03 



Si0 2 i 18. 28 



FeO , 9.06 



IV.sAlA 50 



Cab 99 



MgO 18.16 



Si0 2 23.00 



FeO 4.92- 



A1 2 O 3 2.10 



V J CaO 1. 51 



MgO 8.27 



Fe 3 O 4 (magnetite) 15 



C (graphite) 015 



VI /K 3 16 



' IXajO 68 



From these several values the approximate composition of the mass may be arrived at as given below: 



Iron .' 7.070 



Nickel 730 



Cobalt 031 



Troilite 3.890 



Schreibersite 200 



Olivine 46. 990 



Insoluble silicates 40. 670 



Magnetite 150 



Graphite 015 



99.736 



In the analyses above given the absence of copper in the native metals and chromite among the compounds is to 

 be, noted. Attention is also to be called to the presence of carbon as graphite, occurring as graphitic chondrules, which 

 may or may not be contained in or surrounding particles of the native metals. The occurrence of the graphite is 

 especially interesting, since the relatively large amounts of it do not appreciably affect the color of the groundmass. 



The meteorite is chiefly in the possession of the United States National Museum. 



