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, Sy]. 
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. 
18. CyaLcoryriTe [Cu, Fe, S,]. 
Chalcopyrite is widely distributed over the state in varying amounts, 
but never in such quantity as to make workable deposits, although open- 
