OF ARTS AND SCIENCES. 453 



XIX. 



ON TWO NEW VARIETIES OF VERMICULITES, 



WITH A REVISION OF THE OTHER MEMBERS OF THIS GROUP. 



By Josiah p. Cooke, Jr., 



Erving Professor of Cliemisiry und Mineralogy at Harvard College, 



AND 



F. A. GOOCH, 



Assistant in the Chemical Laboratory. 



Presented, May 11, 1875. 



Since the publication of the writer's first monograph on the vermi- 

 culites,* two new varieties of this group of minerals have been brought 

 to his notice by Mr. W. W. Jefferis, of West Chester, Pa., wlio has 

 most kindly furnished the materials for the following investigation. 



The first of these varieties — which occurs at Lerni, Delaware Co., 

 Pa. — has the following characters : The unaltered mineral is of a dull 

 sea-green color, has a highly developed micaceous structure, is an 

 aggregate of rough hexagonal plates, and of very imperfect external 

 form. It is transparent in moderately thin laminae, and is free from 

 enclo5ed foreign matter. The optical characters of the mineral closely 

 resemble those of the Culsagee variety of vermiculite, the angle be- 

 tween the optical axes varying iu different parts of the same laminae 

 from 18° to 0°. Its hardness is about 1.5, and three determinations of 

 its specific gravity (taken in alcohol at 23° C.) gave 2.409, -2.308, and 

 2.373. Heated in a closed tube, it gives off water acid in reaction, 

 chaniies color, and doubles its volume. Heated before the blowpipe, 

 it fuses to a dirty enamel. 



The mineral was prepared for atialysis by drying at 100° until its 

 weight was constant, and in this condition was easily dacomposed by 

 hydrochloric acid. The bases, after the separation of silica, were con- 



* Tlie Vermiculites, their Crystallographic and Chemical Relations to tlie 

 Micas, by Josiah P. Cooke, Jr. These Proceedings, vol. ix. p. 35. The analyt- 

 ical work in tliis second paper has been done by Mr. Gooch. 



