392 Prof. B. Silliman, Jr., on some American Minerals. 



This mineral when first found, was called Pyrallolite, and is 

 now so labelled in some old collections. Baron Lederer's Cabinet 

 of American Minerals, now in the Yale College collections, con- 

 tains eight or ten specimens of this mineral from Bolton, under the 

 name Pyraliolite, which were received, as the catalogue indicates, 

 from Robinson, Shepard. Nuttall, Boyd, and other of the early cul- 

 tivators of American mineralogy. 



In his remarks on this mineral, Prof. Shepard says, it is believed 

 to be identical with the substance described by Dr. Thomson* 

 under the name of "bisilicate of magnesia ;" and accordingly the 

 analysis of Dr. Thomson is quoted under " Boltonite," as giving 

 the supposed chemical constitution of this substance. 



It will presently be shown that there is every probability that 

 Dr. Thomson applied the name bisilicate of magnesia to another 

 substance, and that the Boltonite of Prof. Shepard is not the sub- 

 stance which he analyzed. 



Having received specimens of Boltonite from Mr. Saemann, 

 a very intelligent and discriminating mineralogist from Berlin, I 

 was induced to undertake an analysis of it which gave me the 

 following results. The specimen analyzed was the yellow varie- 

 ty. 5753 gramme of substance gave: 



. Oxygen. 



Silica, 46-062= 23 93= 8 



Alumina, 5667 264 1 



Magnesia, 38-149 14-76 



Protox. Iron, 8-632 1-95 £ = 17-14 6 



Lime, 1-516 -43 



100 026 



• 



Formula 8Si lAll8Mg=R 2 (Si, Al) or (Mg, Ca, Fe) 2 (Si,Al) 



8 atoms silica = 370*08 =pr. ct. 46-556 



1 atom alumina = 51-47 " 6 -372 



18 atoms magnesia = 372-66 " 47-072 



794-91 100000 



If we consider the alumina as not an essential constituent 

 of the mineral instead of replacing a part of the silica, (a view, 

 which I am not disposed to take,) then we shall have a silicate 

 of magnesia and the other bases, whose formula will be 



• m * • 



R 9 Si*. 



Referring to Thomson's analysis and description of his bisili- 

 cate of magnesia, we read (loc. cit. p. 50) that the mineral received 

 by him from Mr. Nuttall, (from Bolton, Mass.,) bears so much 



* Am. Lye. Nat. Hist., New York, vol. iii, p. 50. 





