CONCRETIONS— FREAKS IN STONE 



By R. S. Bassler 

 Head Curator of Geology, United States National Museum 



[With 3 plates] 



Among the thousands of geologic specimens received for examina- 

 tion every year at the Smithsonian Institution, certain kinds occur 

 very frequently. Among these are dark, heavy rocks mistaken for 

 meteorites; pieces of clear rock crystal or quartz, believed to be 

 diamonds; yellow iron pyrites, sulphide of iron, so often thought to 

 be true gold as to merit its common name " fool's gold " ; and sup- 

 posed petrified animals which usually prove to be concretions, the 

 subject of this paper. The last are probably the most mystifying, 

 and it is diiRcult — indeed sometimes impossible — to convince the 

 amateur collector that they are not what they seem, but simply ag- 

 gregatioAs of mineral matter which, through their method of forma- 

 tion, by chance assume the form of familiar objects. 



In the living world nature runs true to form in reproducing 

 animal and plant species after their own kind, but in the inanimate 

 kingdom she often turns playful and generates most bizarre-looking 

 objects. For example, in the realm of rocks and minerals, geo- 

 metric figures of amazing regularity, specimens resembling living 

 forms, and fantastic objects never seen elsewhere are found among 

 these special rock formations, concretions, some of which are so un- 

 usual that they might truly be called " sports of nature." Many 

 concretions assume such grotesque and marvelous shapes that it i^ 

 no wonder they excite popular curiosity, and in some countries are 

 believed to be of supernatural origin or are called fairy stones, and 

 sometimes are even used as charms. 



Stones, unendowed with life, do not grow like living things by 

 inward accretion, but by external additions. Concretions are the 

 stones that best show this method of growth, for they increase in 

 size, layer by layer over their surfaces, finally forming variously 

 and often very curiously shaped masses of firmly cemented mineral 

 matter. They are found embedded sometimes in porous but often 

 in very impervious rocks, or weathered out at the surface. Their 



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