3+ Count Bournon on certain Minerals brought 



lustre; they belong to the dolomite. The others have a gray 

 tint, and their fracture is less bright; they belong to car- 

 bonate of lime ; but they are mingled with interposed particles 

 of dolomite. 



In this gangue are disseminated some small icosahedrons of 

 pyrites, some crystals of mica, of an orange yellow ; some 

 amorphous particles, and also some regular crystals of apatite, 

 resembling in their green colour the variety called spargel- 

 stein of Spain. It likewise contains a still greater quantity of 

 this substance in small flattened hexahedral prisms, very diffi- 

 cult to recognise on account of a thin white layer which en- 

 tirely covers them ; but when this is removed, the green colour 

 of the apatite appears. I am ignorant whether this white layer 

 arises from an alteration of the apatite, or whether it belongs 

 to another substance which would be completely insoluble in 

 acids ; for it was in dissolving this rock in nitric acid that I 

 obtained these crystals. This gangue contains, besides, many 

 minute particles of magnetic pyrites, and likewise a considerable 

 quantity of small crystals of spinelle, of a fine rose colour. I 

 observed among the latter some complete octahedrons, some 

 with the edges replaced, and some, each of the solid angles 

 of which was replaced by four planes, placed upon the faces, as 

 frequently seen in the pleonaste spinelle of Mount Somma, 

 and which I have also observed in the red spinelles found in 

 the sand of the Ceylon rivers. Some of the yellow crystals of 

 mica have a brilliant lustre, on which account they might be 

 very easily taken for some of the hard stones called gems. 



The memoir on Corundum, which I presented to the Royal 

 Society of London, having been printed in the Journal des 

 Mines for 1803, by referring to pages 97 and 98 of the Num- 

 ber for May of that Journal, it will be seen that this gangue 

 is absolutely of the same nature as those sent to London, from 

 the island of Ceylon, in 1801 or 1802, for the first and the 

 last time*. 



The fourth gangue of spinelle is extremely interesting : it is 

 composed for the most part of spinelle and of mica. The spi- 

 nelle is in octahedral crystals Of a brown colour approaching 

 to violet, and they are much larger than those contained in 

 the gangues above described. The colour of some of them is 

 so deep, that they appear to be black ; they form one of the 

 varieties of the pleonaste spinelle of Ceylon. These crystals, 

 which are extremely abundant in this gangue, are very close 

 to each other, and often form considerable masses, in which 



• See also Phil. Trans, for 1S02, p. 308-311.— Edit. 



