Penfield and Pratt — Occurrence of Thaumasite, etc. 229 



Art. XXIV. — On the Occurrence of Thaumasite at West 

 Paterson, New Jersey ; by S. L. Penfield and J. H. 

 Pratt. 



In 1878 Baron von Nordenskiold* described a mineral 

 from the copper mines of Areskuta, Jemtland, Sweden, which, 

 according to the analyses of Lindstr6m,f had the composition 

 CaSi0 3 , CaCO s , CaS0 4 , 14H 2 and to which the name thau- 

 masite was given, from ^aojud^stp, to be surprised. The min- 

 eral was not found in distinct crystals but was crystalline and 

 on a fracture showed a fine fibrous structure. Its homogeneous 

 character and its right to be considered a distinct mineral 

 species rested upon the following : The material seemed to be 

 homogeneous when examined with the microscope, and the 

 three analyses of Lindstrom, made upon material collected in 

 the early part of this century by Polheimer, in 1859 by Nor- 

 denskiold, and in 1878 by Engberg, agreed not only very 

 closely with one another but also with the theory demanded 

 by the formula. 



That a mineral with such a remarkable composition was 

 capable of existence was not accepted by all mineralogists, and 

 Bertrand4 on examining thin sections of it with the microscope 

 was led to believe that it was a mixture, composed of a uniaxial 

 mineral with negative double refraction supposed to becalcite, 

 of a biaxial mineral gypsum, and of a third mineral, the optical 

 properties of which could not be made out, probably calcium 

 silicate or wollastonite. 



The idea of Bertrand's that thaumasite was a mixture was 

 not accepted by Nordenskiold, and the latter to sustain his 

 position presented the following arguments,! which were very 

 convincing: First, if it were possibly a mixture it certainly 

 would be very remarkable that three independent samples, 

 collected at such widely separated periods, should agree so 

 closely in percentage composition. Second, there is no known 

 hydrated calcium silicate which, when mixed with calcite and 

 gypsum, could yield a product containing over 42 per cent of 

 water. Third, it would not be possible for a mixture of cal- 

 cite, gypsum and wollastonite, with specific gravities of 2*72, 

 2 31 and 2 90 respectively, to yield a product with such a low 

 specific gravity as thaumasite, 1*877. 



Specimens were moreover sent to Lacroix for renewed 



* Oomptes Rendus. vol. lxxxvii, p 313, 1878. 



f Of v. Ak. Stockholm, vol. xxxv, No. 9, p 43, 1878. 



X Bull. Soc. Min. de France, vol. iii, p. 159, 1880, and vol. iv, p. 8, 1881. 



§ Geol. For. Forhandl., Stockholm, vol. v, p. 270, 1880. 



