158 PROCEEDINGS OF THE AMERICAN ACADEMY 



IV. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



Presented by Josiah P. Cooke, Director, June 16, 1886. 



I. — ANALYSIS OF MICA FROM LEON CO., TEXAS. 



By George W. Leighton, B. S. 1886. 



This mica, submitted to our examination by Professor Cooke, was 

 received by him from Dr. A. E. Foote, of Pliiladelphia, wlio ideutifies 

 it as the Joakumite of the Texas Academy of Sciences. The mineral 

 attracted notice, as it presented cliaracteristics intermediate between 

 those of the vermiculites and the muscovites, and it was hoped that an 

 analysis might add to our knowledge of the relations between these 

 species. 



Description. — The mica is opaque except in thin laminte, and has 

 obviously undergone alteration. Cleavage basal eminent, laminae 

 flexible, but brittle and non-elastic. Lustre pearly. Color brownish 

 to yellowish green. Double refraction negative. Biaxial; with bi- 

 sectrix nearly if not absolutely normal to the cleavage, the optical 

 angle in air measuring about 37|^°, but could not be measured accu- 

 rately on account of opacity. In blow-pipe flame the laminag sepa- 

 rate, swelling to more than double the original thickness, and melting 

 on the edges, showing fusibiUty 5-6. Blow-pipe flame strongly col- 

 ored with potash, barely tinged with soda, and with traces of lithia. 

 No fluorine could be detected by the usual tests. 



The Analysis was made in the usual way, fusing with Na^COg for 

 the silica, decomposing with HF for the alumina, iron, and magnesia, 

 and by Lawrence Smith's method for the alkalies. The iron was all 

 in the ferric condition, and was determined volumetrically after weigh- 

 ing AlgOg and Fe^Og together. The potash was weighed as chloro- 

 platinate, and the water was determined by ignition. In the following 

 table, the results of our analysis are given in Column I. In Column 

 II. are the corresponding per cents of oxygen, and in Column III. 



