1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 117 



B. Like A, but more granular. 



0. Paler, nearly white, closer grained. 



D. Brownish, highly foliated. 



All four were analyzed with the subjoiued results : 



Studied in thin sections, under the microscope, the Alaskan nephrites 

 present the following characteristics : 



A. This sample, as seen in the slide and by ordinary light, presents a 

 uniformly colorless field of a homogeneous, nou-pleochroic mineral, and is 

 trausversed by fine wavy rifts running all in the same general direction. 

 The inclosures are very minute, some are mere dust-like particles, others 

 are distinctly recognizable as limouite. Between crossed nicols the en- 

 tire field is covered with very indefinitely outlined areas, which are 

 alternately light and dark as the stage is revolved. With a power of 

 two hundred and thirty diameters these areas are seen to be composed 

 of wavy and uneven scales and bundles of fibers so interwoven and con- 

 fused that no trustworthy measurements of extinction angles are obtain- 

 able. Many of the bundles seem to extinguish in directions approxi- 

 mately parallel with their length ; but others show wide angles. The 

 worked jade, 43415, from Cape Prince of Wales, has essentially the 

 same structure as A, and needs no separate description. No. 43440, 

 from St. Michaels, is also quite similar. In this specimen the fibers are 

 shout and scale-like. There are no inclosures of note, although there 

 is a plentiful sprinkling of amorphous dust-like material. No. 63733, 

 from Diomede Island, is also much like A. It presents no difference 

 which can be considered mineralogically essential, but the texture is 

 more uneven, and many of the fibrous tuft-like masses are larger. The 

 variations, however, are no greater than might occur in samples from 

 the same mass. 



B. This specimen in thin sections and by ordinary light isalso almost 

 colorless, or very faintly greenish, and without pleochroism. It shows 

 only a few yellowish and opaque inclusions, which are evidently of a 

 ferruginous nature. Between crossed nicols it exhibits the well-known 

 nephritic structure — a dense aggregate of short fibers and scales, the 

 fibers arranged in clusters, or radiating tuft-like bundles, without def- 

 inite boundaries, which merge into one another as the stage is revolved. 

 In cases where the bundles are composed of fibers lying approximately 



