SULPHURET OF LEAD, COPPER, AND ANTIMONY. £<* ~ 



I shall not enter into any similar details concerning the 

 other modifications, the number of each of these being af- 

 fixed in each crystal to the planes belonging to it, and the 

 table of these modifications, which will be annexed to this 

 paper, pointing out in this respect at a single view particu- 

 lars, which could scarcely be expressed, by long circumlocu- 

 tion. In consequence I shall confine myself to the follow- 

 ing observations. 



; All the varieties, from fig. 2 to fig. 20 inclusively, are Different v?.ri- 

 met with among the fragments of this substance, that are eaes - 

 brought from Cornwall. I have a very fine groupe of those 

 represented at figs. 7 and 8, and a separate crystal of 8 and 

 of 9. The variety fig. 8 is a regular aggregation, in the 

 form of a cro^s, of two of the crystals fig. 7 elongated paral- 

 lel to the planes or the 6th modification. It might also, 

 and perhaps more justty, be considered as resulting from 

 five crystals, similar to fig. 7, united by one of their planes. 

 I have likewise crystals of the Varieties 11, 12, 14, 15, and 

 19. ; With those at figs. 10, 13, 16, 17, and 18, I was fur- 

 nished by two very fine groupes, and a superb single crystal, 

 iu the possession of Mr. R. Phillips. Fig. iG answers to 

 that numbered 17 in my former paper, which was not quite 

 accurate. In 15 and 16 of the same paper the prism was 

 much too thick, and they are replaced at present by 17 and 

 18. ...... 



I have likewise the varieties from 21 to 26, in a very fine 

 group, which, with the fragments from Peru and Brasil al- 



often of veiy great use to indicate the direction of the laminx of crystal- 

 lization, and not seldom are they the only means, that the crystals of a 

 substance afford. Thus the lenticular rhomboidal carbonate of lime 

 pretty constantly indicates by its str -£ the direction cf the lamina;, and 

 Consequently that of the plants of the primitive crystal. In the hexae- 

 <Jral prism of the same sub-tance, the same stria; point cut the diivcuoa 

 to be given to the fractuies, on which Mr. Hai'y has established the di- 

 Jnensions of its primitive rhomboid. But we must beware of the illusion, 

 that may sometimes arise from suia;, which are indebted for their exist- 

 ence only to an aggregation of crystals, such frequent instance, or * iiiv.li 

 are exhibited by the tourmalin, thalliie, sulphuret of antimony, &c. : 

 an illusion by which 1 have shown 1 was at first misled myself with re- 

 spect lo the eudeliion, after having observed, that among its varieties 

 there existed a rectangular tetraedral prism, the planes of which are 

 frequently striata d. 



ready 



