Count de Bournon’s Description of a 
Mr. Klaproth, of magnesia;* while, according to the 
same chemist, that which comes from Sweden, contains only 
yet both of them, most commonly, assume the primitive 
rhomboidal form of pure carbonate of lime. 
In like manner also, a proportion of iron greater than that 
which makes a constituent part of the garnet, is observed in that 
substance; and this proportion varies considerably, according 
to the circumstances which governed its formation. If we take, 
from among the various analyses of this substance, by different 
chemists, those only which were made by Mr. Vau£uelin, we 
shall find, that the red garnet of Bohemia afforded him of 
iron ; the black garnet of the Pic d’Eres -lids in the Pyrenees 
* This is likewise nearly the proportion of magnesia found in the magnesian car- 
bonate of lime which is so common in Derbyshire, and in many other parts of England. 
For our knowledge of this substance, which had till then been confounded with the 
martial carbonate of lime, (pearl spar,) we are indebted to the analysis made by Mr. 
Tennant. It is found in the form of small but very brilliant crystals, which belong 
to the primitive rhomboid of pure carbonate of lime; but these rhomboids do not 
appear to be subject to those variations in form so commonly met with in martial car- 
bonate of lime. More frequently, however, it is in the form of a more or less granu- 
lated mass, which very often, upon being examined with a lens, shows itself to be 
a confused aggregation of the same small rhomboids. This magnesian carbonate of 
lime, is nearly equal in hardness to the martial carbonate. It dissolves, however, 
much more readily, and with a slight effervescence, in nitric acid; but does not give 
the same yellow colour to that acid, when it happens to contain iron, which it almost 
always does, though in very small proportion. Its mean specific gravity, taken on 
three specimens from different parts of Derbyshire, which varied very little from each 
other, was found to be 2823 ; the same carbonate from Tyrol, gave a mean specific 
gravity of 3053. The specific gravity of the magnesian carbonate is therefore greater 
than that of pure carbonate of lime; and there must surely have been some error in the 
operation that gave to Mr. Klaproth 2480, as the specific gravity of the former 
substance. The magnesian carbonate shows no phosphorescence when thrown upon a 
hot iron. I think it probable that, in th£ cabinets of various mineralogists, specimens 
of it have been erroneously placed among those of pearl spar. 
