THE PRODROMUS 247 



CONCERNING MARCASITES 



The substance of marcasites assumes divers forms, for 

 sometimes it incrusts the surface of a place, sometimes it 

 is condensed into bodies of many planes, sometimes it forms 

 rectangular parallelepipeds ^ which, after the usual mode of 

 speech, we shall call cubes, although regularity of all the planes 

 is found in but a few. 



Since I have had the opportunity to note various matters con- 

 cerning the cubes of marcasites, both the cubes themselves and 

 the place where they are found, I shall speak concerning those 

 matters only ; but their formation, nevertheless, differs from 

 the formation of a crystal : 



1. In time ; since the cubes of marcasites were formed before 

 P- 50. the formation of the strata in which they are contained, whereas 



crystals hardened after the formation of the strata. 



2. In place of production ; for a crystal, at least while it was 

 forming, was resting upon a solid body and so was contained 

 partly in a solid place, partly in a fluid, while the cubes of the 

 marcasites seem to have formed between two fluids, since there 

 are no traces, even in the larger cubes, of cohesion with another 

 body; although small cubes are frequently found which, while 

 growing, adhere to one another in the surface of the fluid. 

 Moreover we are taught by the weighty proofs of the great 

 Galileo ^ that heavier substances of this kind can cling together 

 on the surface of a fluid while one of their surfaces is in im- 

 mediate contact with an overlying and lighter fluid of another 

 kind. That one of the fluids referred to was aqueous, is shown 

 by the matter of the stratum which results from the same fluid. 



3. In the manner and place of accretion ; for the matter of 

 the marcasite is added to all the planes of the cubes in a manner 

 different from that which we have indicated in the case of 

 crystals. This fact is clearly shown by the uniformity of all the 

 surfaces of the cubes which I have myself cut from rocks; all 

 the planes of these had strice parallel to two sides, in such 



1 For Steno's use of the word marcasites, see p. 225, note i. 



" The treatise of Galileo (i 564-1 642) to which Steno refers is entitled Discorso al Serenis- 

 simo Don Cosimo 11, Gran Duca di Toscana, Intorno alle Cose che Stanno in Su VAcqua O 

 Che in Quella Si Muovono. Cf. Le Opere di Galileo Galilei, Edisione Nationale, Firenze, 

 Vol. IV, 1894, pp. 63-141. 



