﻿T. M. Chatard — Lucasite, a new variety of Vermiculite. 375 



completed, are those of the double stars, the four stars with 

 large proper motion, of the Pleiades, of the Prassepe, and of 

 the clusters Lac. 4,375 and Kappa Orucis. The corresponding 

 computations have been made, as yet, only for a portion of the 

 Pleiades impressions, but I am hopeful of completing all these 

 at a comparatively early date. We shall then be able not only 

 to compare the results with Bessel's of 45 years ago, but to test 

 the deduced values of the proper motions by means of the pho- 

 tographic determinations of 1865 and 1866. Meanwhile the 

 valuable memoir of Wolf has been published, giving closely 

 approximate positions for 571 stars of the group, and Dr. Elkin 

 has recently been executing at New Haven a heliometric 

 triangulation of the principal stars. Our photographic results 

 will have to be confronted with his delicate heliometric ones; 

 and should they bear this test with tolerable success, it will be 

 all that can reasonably be desired. 



Art. XLIV. — Lucasite, a new variety of Vermiculite;* by 

 Thomas M. Chatahd. 



In the course of an examination of the minerals occurring 

 with corundum at Corundum Hill, Macon Co., N. C, a vermic- 

 ulite has been found which appears to be a distinct variety of 

 this group. The name Lucasite has been given to it in honor 

 of Dr. H. S. Lucas, so well known in connection with the dis- 

 covery of the Chester, Mass., emery mine and with corundum 

 mining in the South. To him I am indebted for many facilities 

 and much valuable information. 



The specimen from which the material examined was taken 

 was found by me in situ in a corundum vein, and is a mass of 

 a yellowish brown, small foliated mineral, through the central 

 part of which runs an irregular seam of a fine granular, grass- 

 green mineral, shown by analysis to be actinolite, intermixed 

 with a small quantity of chromite and a large proportion of the 

 vermiculite scales, which are however much smaller than those 

 of the outer portions. The separation was made by means of 

 Thoulet's solution, the specific gravity of the actinolite being 

 3*062, while that of the Lucasite is 2'613 (in water 25 "5°). 

 General characteristics as follows : 



Foliated, compact, also disseminated ; folia generally small, 

 not over 2 mm across. Cleavage basal, eminent. Color, yellow- 

 ish-brown, the thinnest scales being almost colorless with 



* From a paper on "Gneiss-Dunyte Contacts," in the forthcoming Bulletin of 

 the Division of Chemistry, IT. S. G-eol. Survey, 1885-86. Communicated by per- 

 mission of the Director. 



