NOTES ON GEOLOGY AND MINERALOGY. lJi9 



SPECIMENS OF TIN-STONES FROM DURANGO. 

 Bt J. H. COLLINS. F.G.S. (Geological Gold Medallist R.LO.) 



The specimens of tin-stones from Mina del Diablo, Durango, 

 Mexico, marked A and B, were handed to me for the Museum of 

 the Royal Institution of Oorn^\rall by Mr. Eichard Pearce, F.Gr.S., 

 in the year 1893. They have been called pseudomorphs of 

 caasiterite after hematite and magnetite, but would be more 

 properly described as simultaneous crystallizations ; the ferrugi- 

 nous component predominating, in quantity and in crystallizing 

 force. The A variety has been well-described and figured by 

 Professors Genth and Vom Eath, and by L. V. Pirsson.* The 

 B variety presents an entirely different appearance, which I 

 have rudely represented in the sketch which accompanies speci- 

 men C. Here it appears that crystals of hematite have been 

 formed in presence of a large quantity of silica, which I believe 

 was at the time in a gelatinous condition ; and around the crys- 

 tals so formed, cassiterite in the radiated and imperfectly 

 crystalline form known as " wood-tin," has been abundantly 

 deposited, so as entirely to enclose the hematite. 



* Genth and Vom Eath, Proc. Am. Phil. Soc, 24, 23, 1887; Pirsson, Am. 

 Jour. Sc, 1891, p. 40. 



