1873.] OJO [Genth. 



21. Chlorite. 



I have mentioned in the geological outline, that chlorite rocks have 

 been observed in almost every locality where corundum occurs in large 

 masses or beds. It remains to examine into a number of peculiar asso- 

 ciations between chlorite and corundum, in order to point out their re- 

 lation to that of the entire chloritic beds. 



a. Near Unionville, in the shaft alongside of the road to Kennett 

 Square, chlorite occurs very conspicuously ; it is intimately mixed with 

 spinel, containing a considerable admixture of corundum (see above). 

 The results of the explorations there, were not sufficiently encouraging, 

 and the mining operations have therefore been abandoned. They have 

 furnished, however, a few interesting scientific facts, as I have shown. 



b. At the principal Unionville locality, chlorite is found under various 

 circumstances. It sometimes forms a lining of minute dark green 

 crystals, between the corundum and the foliated damourite ; then, it is 

 disseminated through the corundum in small scales or seams ; and again 

 it is met with, adjoining the large corundum bed, in boulder-like masses 

 of fine scales, showing a lamination around a centre, which frequently, 

 in breaking them open, consists of a nucleus of granular corundum. 

 This chlorite is of a dull olive-green color, but often under the influence 

 of the atmosphere, converted into reddish or yellowish-brown scales or 

 even a ferruginous clay. 



In a specimen in the University collection of nearly one foot in diame- 

 ter, there seems to have been a fracture in the granular corundum, which 

 allowed the liquid, producing the alteration, to percolate to the centre of 

 the mass, and to deposit in the heart of the specimen, a small quantity of 

 green chlorite, surrounded by a concentric layer of white granular corun- 

 dum, upon which is a layer of scaly chlorite, slightly ferruginous and 

 yellowish in immediate contact with the corundum, graduating into 

 green. The whole nucleus, of about two inches in diameter is enveloped 

 in a mass of yellowish-gray and brownish decomposed chlorite, of which 

 I shall give two analyses by Dr. Koenig. (b, 1 and 2). 



c. Another variety of chlorite from Unionville, originates from the 

 alteration of damourite and tourmaline, which two minerals result from 

 that of corundum. The white pseudo-fibrous variety of damourite (c), 

 gradually assumes a slightly greenish tint from an admixture of fine 

 scales of chlorite, which rapidly increases and soon form a massive 

 variety of a light olive-green finely granular chlorite. The slender tour- 

 maline crystals, which start in the white damourite, pass on into the 

 chlorite, but for a short distance only ; they are soon entirely altered into 

 fine scaly chlorite, and these pseudomorphs of chlorite after tourmaline, 

 are imbedded in the granular matrix like the original tourmaline. This 

 is a highly interesting occurrence, and quite similar to that described by 

 G. Rose (1. c), as occurring in the chlorite slates associated with corun- 

 dum, at Kassoibrod in the Ural. 



Mr. Thos. M. Chatard has furnished me with two analyses, (c, 1 and 2) 

 A. p. s. — vol. xiii. 2x 



