334 
Count de Bournon's Observations on a new 
of which we find no other example in the immense quantity of 
crystallized carbonate of lime that has been hitherto examined, 
however perfect the form of the crystals, or however great their 
degree of transparency. In the second place, why should the 
above-mentioned cause change the character of the crystalline 
forms of carbonate of lime, when we see no instance of such a 
change in the crystalline forms of other substances, even when 
they show, by an increase in their hardness, in their specific 
gravity, and in their transparency, that a closer connection be- 
tween their constituent particles has actually taken place. 
It appears therefore impossible, in the present state of our 
knowledge, to determine the cause of the very great difference 
that exists between the common carbonate of lime and the hard 
kind here treated of ; yet it is equally impossible not to be sen- 
sible, that the said difference is of such a nature as absolutely 
prevents us from considering them as of the same species. 
Whether it is right to join the hard carbonate of lime wfth the 
Arragonite, is a question I have already in some measure dis- 
cussed, but respecting which, until I have had further opportu- 
nities of investigating the matter, I shall not venture to give a 
decided opinion.* 
* I have lately received, from my worthy friend M. Gillet de l’Aumont, 
some imperfectly formed and colourless crystals of hard carbonate of lime, which, he 
says, were found inclosed in lava, near Vertzeu, in the environs of Puy de Dome, 
in Auvergne, and which were considered as a kind of Arragonite. These crystals 
appear to me very similar to the hard carbonate of lime herein described ; and M. 
Gillet informs me, that the above is not the only part of Auvergne in which these 
crystals are found in old lava. I remember perfectly well, that when I was examining 
the volcanic products of that province, on the spot, and also those of Velay, of 
Vivarais, and of Forez, I observed, in many of the lavas of the extinct volcanos of 
those provinces, groups of thin diverging crystals of carbonate of lime, which 
appeared to .me much harder than crystals of common carbonate of lime in similar 
circumstances, so that I found it very easy to, preserve them entire. I think it very 
probable, that the Arragonite cylindroide of the Abbe Hauy ought to be referred 
to this substance. 
