494 PROFESSOR HEDDLE ON THE RHOMBOHEDRAL CARBONATES. 
The analysis was executed on 25°025 grains, and afforded— 

Carbonate of lime, . ; : : d : 51804 
BR of magnesia, , ‘ é ; ; 37°998 
FS ofiron, . ; , : ‘ ‘ 7:82 
PP of manganese, ; ‘ : , : 2°314 
Silica (quartz), 3 : ; : : F "02 
99-956 
This is not the composition of Breunnerite; which is a magnesite, having 
about 10 per cent. of the carbonate of magnesia replaced almost solely by 
carbonate of iron. 
Moreover, neither the specific gravity nor the angular inclination agree with 
Breunnerite—the specific gravity of which is from 3° to 3:2, and its angle from 
107° 22’ to 107° 32’. 
As Ankerite is a Dolomite in which the magnesian carbonate is more or 
less completely replaced by carbonates of iron and magnesia, the Norwick 
mineral falls to rank under that name; though the amount of replacement hardly 
comes up to the limit separating it from Dolomite, as assigned by DANa. 
The equivalentic ratios of its constituents are nearly— 
Ca MgC FeC MnC 
52 43 7 2 
Or more generally— 
(CaMn)C + (MgFe)C 
The lime being to the manganese as 26 to 1, and the magnesia to the iron 
as 24 to 4. 
In gravity and cleavage angle, the mineral agrees fairly with Ankerite; the 
gravity of which is given as low as 2:95; and its angle by Mous at 106° 12’,— 
by Erriine at 106° 6’. 
The theoretical specific gravity of a substance formed with its constituents 
united in the above ratios is 2°94; and its theoretical cleavage angle, 106° 13’. 
Breunnerite, therefore, has to be excluded from the list of British minerals; 
the second analysis repones it, however. 
BREUNNERITE. 
On a hill slope overlooking from the north-west the bay of Haroldswick, 
in the same island of the Shetland group, some exposed portions of weathered 
talc were pointed out; these, on examination, proved to be from a vein running 
through serpentine towards the east coast; and appearing in an indentation 
thereof, called North Cross Geo. After two days’ blasting, unweathered 
specimens were obtained of the following minerals:—Apple-green talc in broad 


