GUIDE TO THE MIXERAEOGIC COLLECTIONS 



81 



Calcite is probably the most widely distributed mineral. 

 Oreat beds of limestone are found among the rocks of nearly 

 every geologic horizon. Calcite also occurs as a vein mineral, in 

 the form of stalactites and stalagmites in caves, and as a fre- 

 quently associated mineral with metallic ores. 



As limestone and marble, calcite is quarried to a considerable 

 extent in Vermont, Georgia, Tennessee, Alabama, California, 

 New York, 1 Pennsylvania and Massachusetts. Calcite in the 

 form of limestone and marble is extensively used as a building- 

 stone; it is also burnt for quick lime, Portland and other cements 

 and is of value as a flux for certain silicious ores. Certain 

 varieties are used for lithographic stone,and the colorless, trans- 

 parent variety is employed in optical apparatus for polarizing 

 light. 



Dolomite (pearl spar) (CaMg)C0 3 



Dolomite is the carbonate of calcium and magnesium con- 

 taining 47.9^ carbon dioxid, 30.4^ lime and 21.7$ magnesia. 



In crystallization dolomite closely resembles the rhom- 

 bohedral forms of calcite. It may, however, be readily dis- 

 tinguished from the latter by the marked curvature of the rhom- 

 bohedral faces (pi. 26J. Massive coarse or fine granular 

 varieties are distinguished with difficulty from the correspond- 

 ing forms of calcite. 



The luster of dolomite is vitreous to pearly; the color is com- 

 monly white, pink or gray and less frequently rose-red, green, 

 brown or black. 



Dolomite in the form of dolomitic limestone constitutes exten- 

 sive strata in many geologic formations and forms a series from 

 pure limestone to pure dolomite. Compact and crystalline varie- 

 ties frequently occur with serpentine and other magnesium 

 minerals. 



In New York dolomite is found at Lockport and Niagara Falls, 

 Niagara co.; at Brewster, Putnam co.; Union Springs, Cayuga 

 <io., and in many other localities. 1 



It is used for much the same purposes as calcite. 



*N. Y. stato mus. Bui. 15. 1896. 



