1 62 Dr. Wollaston on the primitive Crystals , &c. 
perfectly free from carbonate of lime, as to render it highly 
probable that in other specimens, having the same angle, but 
containing also carbonate of lime or other ingredients inter- 
mixed, the form is really dependent on the carbonate of iron 
alone. 
It appears, however, not unlikely that when substances, 
which agree so nearly in their primitive angle, are intermixed 
in certain proportions, they may each exert their power; and 
may occasion that confused appearance of crystallization with 
curved surfaces, known by the name of pearl-spar. I cannot 
say that I have made any accurate comparative analyses which 
may be adduced in support of the hypothesis, that mixtures 
are more subject to curvature than pure chemical compounds ; 
but it is very evident, from the numerous analyses that have 
been made of iron-spar by other chemists, how extremely 
variable they are in their composition, and consequently how 
probable it is, that the greater part of them are to be regarded 
as mixtures ; although it be also possible, that there may exist 
a triple carbonate of lime and iron as a strict chemical com- 
pound. 
It seems not unlikely, that there may hereafter be found 
some carbonate allied to the preceding, which may owe its 
form to the presence of manganese ; but notwithstanding the 
liberality which happily prevails in general among those who 
have it in their power to assist in such inquiries, I have not 
had the good fortune to meet with any such compound ; and 
I am unwilling, merely in the hope of making such an addi- 
tion, any longer to defer communicating an observation, which 
I hope will be of real utility in the discrimination of bodies * 
that differ so essentially in their composition. 
