32 MINERALOGY AND LITHOLOGY. 



material of some metallic veins, as, for example, at Croydon mountain. 

 Shelburne, Unity, Warren, Haverhill, Red hill in Moultonborough, Rich- 

 mond, Lebanon, Lyme, Lyman, Gardner mountain, and Monroe may be 

 mentioned as places where it is to be obtained in abundance, while hun- 

 dreds of square miles of the state are covered with pyritiferous rocks, 

 and it is common everywhere in little veins. It is often found in crys- 

 tals, the prevailing forms being, as usual, the cube with the planes of the 

 pentagonal dodecahedron. The crystals are often much distorted by the 

 oscillation between these two forms. 



Pyrites is a very common ingredient in rocks ; and, as its presence is 

 very deleterious in stones that are to be used for building purposes, a 

 careful examination of them is advisable, as, if pyrites be present, it de- 

 composes on exposure, and stains the stone. When present in consider- 

 able amount, it can be recognized with the naked eye, since its brassy 

 yellow metallic lustre makes it conspicuous ; and the minutest particles 

 of it can be recognized in microscopic sections by turning away the light 

 from below the stage of the instrument, when the pyrites, with its bright 

 yellow reflection, is very evident. In the slates and greenstones of the 

 Connecticut valley, it is often found in the most minute microscopic and 

 still perfect cubes. 



17. Marcasite [Fe, S^]. 



This, the dimorphous form of iron bisulphide, has been found at 

 Haverhill, associated with ordinary iron pyrites and the various other 

 sulphurets that occur there. Marcasite is orthorhombic, has a lower 

 specific gravity than pyrite, and, on account of its lighter yellow color, 

 is called white iron pyrites. The Haverhill mineral is found in fibrous 

 radiated masses. The crystalline form is not evident, but it is plainly 

 prismatic. It decomposes more readily than common iron pyrites; and 

 the outside of the fibrous masses is often changed into the hydrous oxide 

 of iron. All these characters make it easy to distinguish, though its 

 chemical reactions are like those of pyrites. 



iS. ClIALCOPYRITE [Cu, Fc, Sj]. 



Chalcopyrite is widely distributed over the state in varying amounts, 

 but never in such quantity as to make workable deposits, although open- 



