GUIDE TO THE MINBBALOGIC COLLECTIONS 81 



I lalcite is probably the most widely distributed mineral. 

 Great 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 ;i 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)CO.. 



Dolomite is the carbonate of calcium and magnesium con- 

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



Jn 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. 2Gj). 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 

 pnre 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 eo.; at Brewster, Putnam co.; Union Springs, Cayuga 

 CO., and in many oilier localities. 1 



It is used for much the same purposes as calcite. 



X. V. sen.- muB. P.ul. 15. 1896. 



