125 



TAB. CCCLXVI. 



FERRUM sulphureum. 

 Sulphur et of Iron. 



Class. 3. Metals. Ord. 1. 

 Gen. 8. Iron. Spec. 5. Sulphuret. 



Biv. 1. Crystallized. 



1 his singular formation of Pyrites, although of old in my 

 collection, is, I believe, new in description. Crystallo- 

 graphers say very little of the concave or convex rounding 

 of crystals of any sort, although it is often a strong charac- 

 teristic of some substances, especially the convex, as in the 

 Diamond : — Crystallography, part 2d, and Galaena, tab. 131 

 of this work, &c. The concave is, however, much more 

 rare : indeed the appearance is so extraordinary, that it has 

 been looked at more with an eye of wonder than investiga- 

 tion. The present specimens are examples of this concave 

 formation, and of the tarnish and iridescence which partly 

 disguise substances. They are nearly the same within, 

 although the smallest is so light- coloured outside, and has 

 a yellow, red, and blue iridescence ; and the other nearly a 

 fair yellow metallic tarnish. This latter specimen also shows 

 the convex formation, which is so great a contrast to the 

 former that it is altogether a wonderful group, whether 

 caused by the solvent or quantity of material attracted for 

 aggregation. It seems to be an accumulated repetition of 

 this formation that represents the Cockscomb of the fol- 

 lowing table. We have, however, still some very valuable 

 and extraordinary specimens that primarily lead to this pe- 

 culiarity, of which we shall be happy to make observation, 

 as they are truly instructive. 



