360 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 99 



"Enstatite. About two-thirds of the nonopaque insohible material 

 is composed of enstatite. The enstatite grains are minute ; the crushed 

 grains show distinct prismatic cleavage. Its color is gray ; colorless in 

 thin fragments. Luster vitreous. Transparent to translucent. Opti- 

 cally positive with a large axial angle, 2F=T5°— 78°. Dispersion 

 distinct, r>v for most grains. The indices of refraction are : a= 1.659, 

 /8= 1.664, y= 1.670. The composition of the enstatite, estimated from 

 the optical properties, is En 93-94FS 6-7. 



"Chrome diopside. This green pyroxene is less abundant than the 

 enstatite in the insoluble residue. Its grains are rounded, transparent 

 to translucent. Optically positive; 2F approximately 60°. Disper- 

 sion distinct, r>v. Indices of refraction: a= 1.689, /?= 1.695, 

 y= 1.704. Birefringence measured in bakelitic mount by comparison 

 with quartz using Berek compensator 0.0264. Optical angle 55° — 60° ; 

 ZA(7 39°-40°. 



a= 1.6766, Na light on temperature cell. 



;8= 1.6828, calculated. 



7=1.7030, calculated from birefringence. 

 This pyroxene has enstatite exsolution lamellae perfectly developed 

 paralled to (001), which indicates very slow cooling in its original 

 environment. Estimate composition from the optical properties is 



W046En48FS6. 



"Oligoclase. This feldspar is present in amounts equal to the py- 

 roxene. Colorless with a good cleavage. Optically negative; 2F 

 moderately large. Indices of refraction are: a= 1.538, /3= 1.543, 

 y= 1.546. These properties indicate a composition close to AbgoAuao. 



"Maskelynite. A small amount of an isotropic material with an 

 index of refraction of 1.539 was observed which is probably mask- 

 elynite." 



COMPOSITION OF THE SILICATES IN LINWOOD, NEBRASKA, METEORITE 



Olivine Fo9„Fa4o 



Enstatite En93-94FsFse-7 



Chrome diopside WowEn^sFsa 



Oligoclase AbsoAnjo 



Chemically the pyroxenes are in equilibrium. 



Carbon is distributed through all the inclusions but not always 

 uniformly within each inclusion. Troilite is usually more or less 

 concentrated around the rims of inclusions, bordering the metal. 

 Only a few schreibersite bodies were observed in these inclusions, but 

 they seem always to occur adjacent to the metallic iron and not as 

 isolated masses in the graphite and silicate material. 



U. r. GOVERNMENT PRINTING OFFICE: 1949 



