396 S. L. Ptnfield — Mineralogical Notes. 



Li[Al(OR).,],Si 2 O c . Below will be found the author's analysis 

 simplified by regarding all of the alkalies as represented by 

 their equivalent of Li 2 0, the Fe 2 0, as A1 2 3 and the F as OH 

 and the whole calculated to one hundred per cent, also the per- 

 centage composition from the proposed formula. 



Analysis as adjusted. Theory. 



Si0 2 34-46 35-09 



A1 2 3 45-95 44-74 



Li o 4-21 4-38 



H„0 15-38 15-79 



100-00 100-00 



The agreement is certainly satisfactory and the discrepancy 

 is probably the result of some slight impurity, which it is hard 

 to avoid in micaceous minerals. Most of the water is expelled 

 from cookeite at a high temperature, showing that it is proba- 

 bly formed from hydroxyl as assumed in the formula given 

 above. The analysis was made on air-dry powder and the fol- 

 lowing fractional determinations were made : 



Twenty hours over sulphuric acid in a desiccator, 0*82 per cent loss. 



One hour at 100° C 0-09 " " 



One hour at 300° C. (to constant weight) .... 0-91 " " 



Total ...1-82 " " 



If this small amount of water is deducted from the analysis 

 the ratio of Si0 2 : H 2 is nearer 4 : 5 but the formula then 

 becomes much more complicated. 



The essential difference between the author's analysis and 



that of Mr. Collier is in the alkalies, and it is impossible to 



give any explanation of his potash determination except that 



the material for the same was possibly contaminated with 



lepidolite. 



Mineralogical Laboratory of the Sheffield Scientific School, 

 New Haven, January, 1893. 



Aet. XLYII. — Mineralogical Notes; by Samuel L. 

 Penfield. 



The author takes this opportunity of expressing to the 

 Director of the U. S. Geological Survey his obligations for the 

 privilege of presenting the results of the following mineral- 

 ogical studies, which have been made upon material collected 

 by the writer during the summer of 1892, while engaged in 

 survey work. 



