MINERALOGY. 127 



has been found at Bath, Bedford, and Walpole, in small, grayish-white 

 efflorescences. It is easily recognized by its astringent taste. It is iso- 

 metric in crystallization, but is usually found in mealy crusts, 



S9. Calcite [Ca CO^]. 



Calcite, although abundant enough in New Hampshire, is generally 

 found in the massive condition, forming limestones, or, mixed with other 

 minerals, forming calcareous rocks : hence its consideration belongs 

 chiefly to lithology. Good rhombohedral crystals of calcite are, how- 

 ever, found at Amherst, Surry, Warren, and the Notch. The variety of 

 calcite called argentine is found at the iron mines in Lisbon. It is called 

 argentine on account of its silvery lustre. 



In its more ordinary forms, calcite is widely distributed. It occupies 

 veins in other rocks, as at Portsmouth, where it usually shows large 

 cleavage surfaces, indicating coarse crystallization. It also forms thick 

 beds interstratified with the surrounding rocks, as at Orford, Haverhill, 

 Meredith, and Littleton. At the latter place it is filled with fossils ; and 

 the accumulation of beds of limestone is supposed to be largely due to 

 the various organisms, whose calcareous shells are so often found in them. 

 When the last remnants of this organic life have been destroyed, the 

 limestones are white, while otherwise they are blue or gray. 



Calcite is constantly met with in thin sections of some classes of our 

 rocks, sometimes as an original component, and sometimes as a second- 

 ary product. As a constituent of the basic eruptive rocks, it has plainly 

 resulted from their decomposition, since it is usually found in little cav- 

 ities, though it is also scattered all through the rock, as can be proved 

 by moistening them with hydrochloric acid, and watching for an effer- 

 vescence. Such minerals as pyroxene, by slow acting agencies, give 

 up a part of their lime, and are converted into chlorite, while the basic 

 feldspars quite easily part with theirs, as was shown in the discussion 

 of anorthite. Thus results the calcite which so commonly fills all the 

 pores of such rocks, and by such processes the lime has been separated 

 from the original basic rocks to form beds by itself. 



The microscopic characters of calcite, as seen in thin sections, are 

 very characteristic. It is strongly double refracting, and the light 

 which passes through a crystal with its vibrations in a plane par- 



