218 Decomposition of Iron Pyrites. 



discolored ; a well known example of this is shown in the unfor- 

 tunate staining of the white marble from Lee, Mass. (Pyrite 

 No. 57, Sp. Gr. 4.949), in the walls of the County Court 

 House in New York City, after weathering less than twenty 

 years. Observations of this character have led to the broad de- 

 nunciation, in general text-books dealing with the subject, of all 

 pyrites, without discrimination, as the source of injury to 

 building-stones, often in cases due to other causes and de- 

 fects. The popular distrust of pyritiferous stone thereby gen- 

 erated, has doubtless resulted in the rejection of quantities of 

 valuable and durable building materials. 



Dr. Geo. W. Hawes has protested^ against these unwise and 

 exaggerated statements, on the following ground : '* There are 

 other peculiarities of decomposition regarding which too abso- 

 lute rules have been laid down. Pyrites is considered to be the 

 enemy of the quarryman and constructor, as it decomposes with 

 ease and stains and discolors the rock. But here, too, there are 

 features, which very seriously modify the effect of this decom- 

 posing substance. Pyrites, in sharp, tvell defined crystals, some- 

 times decomposes with great difficulty. If a crystal or gi-ain of 

 pyrites is embodied in soft, porous, light colored sandstones, 

 like those which come from Ohio, its presence will with certain* 

 ty soon demonstrate itself by the black spot which will form 

 about it in the porous stone, and which will permanently dis- 

 figure and mar its beauty. If the same grain of pyrites is sit- 

 uated in a very hard, compact, non-absorbent stone, the 

 constituent minerals of which are not rifted or cracked, this 

 grain of pyrites may decompose and the product be washed 

 away, leaving the stone untarnished.*' In the passage above 

 italicised, there is implied a recognition of a broader ground of 

 view, one which we may now more clearly see to be founded on 

 an exact discrimination, not only of the crystalline species of 

 the pyrites occurring in any stone, but also of its internal con- 

 stitution, especially its proportion of enclosed or intermixed 

 marcasite. T. Egleston also remarks:'^ "As a general rule 

 when a limestone contains much pyrites it should be discarded, 



' Report on the the Building Stones of the U. S. , Introduction, page 13, 

 Tenth Census of the U. S., (1880), Vol. X. 

 '■' Trans. Am. Soc Civil Eno;., (1886) XV, 670. 



