252 



DESCRIPTIVE MINERALOGY. 



Columbia County. This mineral has been found in efflorescences on the slate near the city 

 of Hudson, and it is similarly found in the vicinity of Buffalo in Erie county. 



Essex County. Efflorescences of epsom salt and sulphate of lime form in dry weather 

 on the banks of clay in the neighborhood of Crown-Point, and it may be collected in a pure 

 state. Some wells in Addison, Vermont, in the same clay, are so highly charged with this 

 salt, that they cannot be used except as reservoirs of rain water. A portion of saline water 

 taken from the spring near Crown-Point, had a specific gravity of 1.014. 1000 parts by 

 weight contain 18.78 saline matter, the greater part of which is sulphate of magnesia, with 

 some sulphate of lime.* 



Monroe County. Efflorescences similar to those already described, are found on the lime- 

 stone and shale below the Genesee falls, near the city of Rochester. It is here, however, 

 usually mixed with common salt and a little sulphate of soda. 



Oneida County. Some locahties of epsom salt have been noticed in this county. 



Rensselaer County. Three miles above Lansingburgh, on the Hudson river, it occurs 

 in efflorescences on clay. After a long drought, the whole face of the bank is often nearly 

 covered with the salt. The marly clay which forms the bank contains magnesia and iron 

 pyrites, the latter in very minute grains and in variable proportions.! 



MAGNESIAN CARBONATE OF LTME. 



Magnesian Carbonate of Lime. Cleaveland. — Chaux Carbonatee Ferrifere Perloe, and Chaux Carbonatfe 

 Magnesifere. Haily. — Calcarco-Carbonate of Magnesia. TTiomson. — Bitter Spar. Phillips. — Dolomite, or 

 Macrotypous Limestone. Jameson. — Makrotypes Kallc-Haloicl. Mohs. — Gurhofian. Klaproth, and Mohs, 

 App. — Dolomite. Shepard and Dana. 



Description. Colour white, generally inclining to red or green, 

 red, brown, grey and black, owing to foreign admixtures. Streak 

 greenish white. It occurs regularly crystallized ; also massive and 

 disseminated. The primary form is a rhombohedron. Fig. 126. 

 P on P 106° 15'. Cleavage parallel with the primary rhombo- 

 hedron. Fracture splintery, conchoidal and slaty. Lustre vitreous, 

 inclining to pearly in some varieties. Varies from transparent to 

 translucent on the edges. Brittle and easily frangible. Hardness 

 from 3.5 to 4.0. Specific gravity from 2.81 to 2.88. 



Before the blowpipe, this mineral is scarcely distinguishable from 

 calcareous spar. Some varieties, however, become harder and 



assume a darker colour. It dissolves slowly and without much effervescence in acids, by 



which it may in general be distinguished from carbonate of lime. 



Varieties. Miemite. This has a greenish white or green colour. Internally it is splen- 

 dent and pearly. Fracture foliated and curved. It occurs crystallized and massive. 



'Emmons. New-York Geological Rfportt, 1838. 



fEatOD. American Journal of Science. XV. 242. 



