from Ceylon and the Coast of Coromandel. 35 



some of them are in contact with others, and even penetrate 

 them. 



The mica is of a brown yellow colour, slightly orange by 

 refracted light; it forms, in this gangue, considerable masses, 

 to which we may give the name of " mica en masse lameUaire.'" 

 The detached parts of these masses are perfectly transparent, 

 and have a very brilliant lustre. By means of nitric acid I have 

 extricated one of them, of the dimensions of two inches by 

 one inch and three lines, from the carbonate of lime, which con- 

 stitutes a part of the gangue; this mass is perfectly pure, with 

 the exception of some insoluble particles which it contains; 

 among which are particles of magnetic pyrites. I have never yet 

 seen mica in such considerable masses presenting so beautiful 

 and brilliant an aspect. The mica, which in this specimen is 

 very pure, has sufficient solidity to resist pressure, and is con- 

 sequently very suitable for the illustration of what I asserted 

 for the first time in 1813, in the summary catalogue of my 

 collection, now become that of the King, that the integrant 

 particles of mica are of themselves of very great hardness, and 

 that this substance is so easily broken on account of the weak- 

 ness of the cohesive force which unites these particles to each 

 other; but that, when small fragments or crystals of mica 

 have sufficient thickness to resist pressure, they cut glass with 

 facility, and will even scratch quartz, or at least deprive it of 

 its polish, a fact which is further confirmed by the nature of 

 its refraction, as well as by that of its reflective power*. The 

 King's private collection possesses a suite of specimens of mica 

 for study, which presents this extremely interesting substance 

 under a great variety of aspects very little known. This 

 suite, which in my opinion is unique, should be consulted in 

 order to obtain a complete knowledge of this substance. 



The fifth gangue is very particular: it is a girasol, mixed 

 with particles of a slightly grayish white, with some of a yel- 

 lowish green, and with others in the state of girasol jasper, on 

 account of the hydrate of iron which is interposed in them. 

 The specimen placed in the Royal collection has adhering to 

 it a small piece in an earthy slate, mixed with much brown 



* All these characters induce me to believe that this fourth gangue 

 of Ceylon spinelle is the same as that, which, according to Dr. Davy, 

 forms hills in the vicinity of Candy, and in which he likewise observed cry- 

 stals of ceylanite, which he seems to consider as a different substance from 

 spinelle. I am ignorant of his reasons for making this distinction : cey- 

 lanite, it is true, contains a large proportion of iron, but the quantity of 

 that metal varies in the different analyses which have been made of 

 spinelle ; I think, therefore, that it is merely interposed in the ceylanite. 



E 2 mica, 



