DR T. THOMSON'S Analysis of some Minerals. 473 



It is unfortunate that the crystals in the specimen which I 

 possess do not admit of measurement. The angle of the rhom- 

 boid constituting common carbonate of iron is known to be 107. 

 Probably the measurement of the present species will deviate 

 somewhat. 



Third variety. 



This variety is implanted in small sphericles on the points of 

 long crystals of quartz. Its colour is brownish, and its lustre ra- 

 ther inclined to pearly. But in every other respect its charac- 

 ters are those of calcareous spar. Its specific gravity is 2.727- 

 Its constituents were found to be, 



Carbonic acid, . . . 44.405 



Lime, 56.090 



Magnesia, ......... 1.650 



Protoxide of iron, . . 1 .465 

 Alumina, . . . -' ^if'tto 1.120 



104.73 



The carbonic acid is little more than sufficient to saturate the 

 lime ; I have little doubt, however, that the magnesia is also in 

 the state of carbonate. The iron and alumina were probably 

 only accidental. It is obvious that this mineral is not a true 

 species, but merely a variety of common carbonate of lime. Its 

 locality was Transylvannia. It was marked Globular Brown 

 Spar. 



Fourth variety. 



It was composed of a congeries of small rhomboids with 

 curved faces. 



Lustre pearly. 



Surface brown ; but the interior of the mineral which had 

 not been exposed to the weather snow-white. 



Scratches calcareous spar, but not fluor-spar. Hardness 3.5. 



Opaque, or only slightly translucent on the edges. 



