340 Mr. William Phillips on the Oxyd of Tin. 



that some modifications of the primitive crystal of this substance are 

 principally the production of particular districts, as I am led to 

 suspect will be the case, might not an investigation of the nature and 

 peculiarities of the veins, and of the country through which they 

 pass, tend to throw some light on the circumstances, or laws, by 

 which the several modifications are produced : may not these cir- 

 cumstances be supposed in some degree to depend on the purity of 

 the substance itself, or to be affected by the various proportions of 

 other substances entering into combination with it ? The Bohemian 

 oxyd has not hitherto been observed to assume so great a diversity 

 of crystalline forms as the Cornish, which by the analysis of 

 Klaproth already noticed, appears to be by far the most pure. 



The crystals of this substance from Bohemia are generally much 

 larger than those from Cornwall, but Pryce mentions one he had 

 seen that weighed upwards of two ounces. Very large crystals, 

 mostly of the made, 1 believe, were found in Seal-hole and Trevonance 

 mines in St. Agness ; in the former they were lying loose in the 

 vein, and were conveyed without first breaking or purifying them, 

 immediately from the mine to the smeking-house. Some have also 

 lately been brought from a mine in the neighbourhood of the 

 Tamar, and others from near the Land's End ; but instances of this 

 kind are by no means common. The crystals of this substance are 

 generally in part imbedded in the matrix ; they are not commonly 

 so disposed as to shew both paramids, and are sometimes confusedly 

 grouped, but this appearance of confusion principally arises from a 

 circumstance which will be hereafter explained in speaking of the 

 made, to which the oxyd of tin is so liable. The crystals are rarely 

 disposed in radii, but I have one specimen on which they are so 

 disposed. Radiated schorl has often been mistaken for tin, to 

 which it frequently bears considerable resmblance. 



