4 PROCEEDINGS OF THE AMERICAN ACADEMY 



sible that a simple mixture of the two should become as magnetic as 

 magnetite. 



On referring to the analysis made by ^Ir. L. G. Eakins in the labo- 

 ratory of the United States Geological Survey, it appears that the 

 composition of the dark olivine somewhat resembled that of hyalosi- 

 derite, — a variety of olivine which might be strongly magnetic. The 

 question then arose as to whether the zone of dark olivine owed its 

 magnetism to the composition of the olivine, or whether it was due 

 to an admixture of a magnetic variety of sulphide of iron. 



It was very difficult to obtain pieces of the dark olivine free from 

 veins of troilite, but with sufficient care quite large fragments could 

 be picked out, which under the microscope showed a somewhat resinous 

 lustre, and a color varying from black and opaque to transparent red 

 and yellow or colorless, but with no signs of any characteristic grains 

 of troilite. After grinding the material to powder, the darker specks 

 could be separated by the magnet, leaving the light transparent part. 

 The magnetic portion thus selected would gelatinize with acid, but 

 also invariably would give the reaction for sulphur, although showing 

 no other characteristics of troilite even when examined in a thin sec- 

 tion under the microscope. The same material was found in the 

 Pallas and Prehistoric specimens, thoui>h of a still darker color and 

 giving a far stronger sulphur reaction. When it became evident 

 that the sulphur was a constant accessory of the magnetic olivine, it 

 precluded the possibility of the olivine being a distinct variety, like 

 hyalosiderite. 



The distribution of the dark olivine mainly near the exterior of the 

 mass and along the crack, with only occasional patches in the interior, 

 would suggest its being an alteration product. This appeared still 

 more probable after examining a thin section of one of the dark olivine 

 crystals. It was seen at once that the crystals of olivine were intact 

 except for a dark deposit along the cleavage cracks. "Where the dark 

 portion bordered on the green, the olivine was somewhat discolored, 

 red or yellow, but evidently it had not undergone any change from 

 weathering. It seemed more as if the dark portion had been fused 

 and drawn into the cracks of the olivine. Experiments were there- 

 fore made to see what the effect would be of fusing the olivine and 

 troilite of the Kiowa County pallasite, and it was found that, if non- 

 magnetic troilite and crystals of transparent green or colorless olivine 

 were heated together out of direct contact with the air, and the tem- 

 perature raised to near the melting point of the olivine, the troilite 

 would turn black, become strongly magnetic, and permeate all the 



