S6 M. Repetti on Quartx Crystals and Siliceous Paste 



sawn in his own presence the shaft of a great column for the 

 new church of St Fran9ois at Naples, perceived a lucica. This 

 led him to probe the marble with an iron, when in an instant, 

 and to the great surprise of all those who assisted at the ope- 

 ration, there was seen a cavity larger than usual, every where 

 lined with crystals, and containing about a pound and a half 

 of liquid. With still greater astonishment they saw at the 

 bottom of the cavity a transparent pjvtuberance as large as 

 the Jist, and which seemed to have all the characters of rock 

 crystal. Transported with the idea that he was about to 

 possess himself of the purest specimen of hyaline quartz in the 

 world, he instantly attempted to detach it from its matrix ; but 

 alas ! he had scarcely withdrawn his hand from the cavity be- 

 fore he saw an elastic and pasty substance, which at first might 

 have taken any shape, and received any sort of impression. 

 It soon, however, became solid and opaque, when it had the 

 aspect of calcedony, or of a fine porcelain biscuit. Disap- 

 pointed by this unfortunate metamorphosis, and putting no 

 value on a substance, the whole importance of which seemed 

 to him to be gone, M. del Nero threw it in vexation among 

 the debris of marble collected in the ravine." 



Such is the account given in the very words of M. Repetti. 

 This naturalist does not dissemble that it may be considered 

 incredible ; but, according to him, every person present gives 

 the same account, and among these were several well worthy 

 of credit. Besides, he adds, the fact quoted by M. del Nero 

 is not unique, though examples of pasty crystals as large as 

 his have not occurred. 



When Spallanzani visited Carrara in 1783, the workmen 

 told him that they sometimes found in the marble crystals 

 which became hard after they were taken out. " But I have 

 discovered," says Spallanzani, " that this opinion is not true. 

 The quartz contained in the marble is as hard before its ex- 

 traction as after it is exposed to the air, which is also perfectly 

 conformable to the laws of crystallization." To this positive 

 denial of the fact related by M. Nero, M. Repetti replies, that 

 M. Spallanzani misunderstood the workmen, and that he mis- 

 took for a general law what was stated to him only as an ex- 

 ception. 



