AT THE TOURMALINE LOCALITY, CHESTERFIELD. 297 



from a letter of Mr. A. A. Hayes, to whom I submitted a portion 

 for examination. After detailing his proceedings, he observes : 



" From these experiments it appears that the mineral is a nearly- 

 pure oxide of tin, its hardness and closeness of texture, as indicat- 

 ed by its high lustre, exceed those of any specimen I ever ex- 

 amined. You have the satisfaction now of settling the question 

 which has been so long agitated in relation to oxide of tin having 

 been found in Massachusetts." 



Its physical characters are as follows : color black, lustre almost 

 metallic, with external iridescence ; powder of streak pale clay 

 color ; some of the very minute crystals are translucent, and of that 

 peculiar brown color so well known in oxide of tin ; the quantity 

 of crystals found does not exceed half a dozen, the largest^ of 

 which is one line at the base of the pyramid. Form, an obtuse 

 octahedron, with a square base, formed by the second modifica- 

 tion of Phillips, in his paper in the second volume of the Trans- 

 actions of the Geological Society of London, which answers to 

 modification/, of Brooke. On the minute crystals, Phillips's fourth 

 modification is very distinct ; it answers to Brooke's modification^ 

 but the planes of n are not sufficiently clear for measurement. 



I obtained the following measurements with the reflecting goni- 

 ometer, which are sufficiently approximative to those of Phillips, 

 to leave no doubt on the form, considering the usual difficulty of 

 measuring crystals of tin. 



Phillips. 

 / on /' on adjacent planes of pyramid, 121.25' " 121.40' 



/ on / over summit, . . . 92.50' " 92.55' 



/ on / over the base of the pyramids, 87.15' " 87.5' 



I did not find any twin crystals, as mentioned in Mohs. 



In reference to the above, and the mineral Pyroclilore found by 

 Prof Shepard at this locality, Mr. Hayes observes : 



" There is an interesting feature in this connection disclosed by 

 the examination made of the Titaniferous Tin and Cerium oxides. 

 The titanic oxide does not prohahly unite with the oxide of tin, 

 and our mineral, (pyrochlore,) probably consists of oxides and 

 silicates crystallizing in common." 

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