Clarke — Pseudo-Serpentine from Washington. 397 



Art. XL. — A Pseudo- Serpentine from Stevens County, 

 Washington ; by F. W. Clarke. 



In the course of an investigation upon the ornamental stones 

 of Stevens County, Washington, Mr. R. W. Thatcher and 

 Professor Elton Fulmer, of the State Agricultural Experiment 

 Station, examined a supposed serpentine which proved to have 

 quite anomalous composition. To the unaided eye the rock 

 was ordinary serpentine of a typical yellowish green color; it 

 was fairly homogeneous, and capable of receiving a fine polish. 

 Incomplete analyses, however, by both of the above named 

 chemists showed that it was not serpentine, and as I had been 

 consulted with regard to the interpretation of the data, a sample 

 was sent to me for more exhaustive study. 



According to Professor S. Shedd of the Washington Agri- 

 cultural College, who is conducting the investigation, the 

 rock is from the quarry of the United States Marble Company, 

 12 miles north and west from Valley, a station on the Spokane 

 Falls and Northern Railroad. It outcrops on the face of a 

 high bluff at an elevation of about 4,070 feet above sea level, 

 and forms a wedge-shaped mass cutting across the mountains 

 in a direction 5° west of north. The adjacent rocks are slates, 

 which lie conformably upon a very coarsely crystalline, dark, 

 almost black, magnesian carbonate. The " serpentine" itself 

 varies a good deal in color, and a series of samples in the U. S. 

 National Museum show that the output of the locality is far from 

 uniform. They range from a white carbonate, through various 

 intermediate mixtures of the verde antique type, to material 

 which appears to be ordinary serpentine. The latter, however, 

 as shown by the serpentine under consideration, is distinctly 

 laminated in structure, and exhibits a splintery fracture. An 

 analysis by Mr. George Steiger gave the following results : 



Si0 2 _. 13-08 H 2 Oatl00° -85 



A1 2 G 3 1-63 H 2 at above 100° 23-94 



Fe 2 3 1-25 C0 2 2-03 



FeO -19 



MgO __ _.. 56-44 99-74 



CaO -33 



These figures at once suggest a probable admixture of bru- 

 cite with the serpentinous material, and a microscopic examina- 

 tion by Mr. J. S. Diller tends to confirm this supposition. 



According to Mr. Diller the specimen is mainly composed 

 of three minerals, a, h, and c. The first two have nearly equal 

 indices of refraction, but differ widely in birefringence. The 

 mineral a is the most abundant. In transmitted light it is 



