220 Discovery of Columbite in Chesterfield^ Mass, 



COLUMBITE. 



In May, 1828, while on a visit to the remarkable deposit ot 

 tourmahnes in Chesterfield, Mass., my attention was called 

 to a loose rock in the foundation of a stone fence, by the large 

 and delicate folia of yellow mica it contained. The mass 

 bore signs of having had fragments detached from it before; 

 but the wall being now displaced for the purpose of affording 

 a passage to cattle, I was enabled with the aid of a hammer, 

 to reduce it completely to fragments. Towards its centre, I 

 found imbedded, a number of black metallic crystals, whose 

 form and weight led me at once to think of Columbite. They 

 were situated within a few inches of each other; sometimes 

 engaged in feldspar, at others in beryl, and occasionally, 

 between the folia of the mica. They presented much di- 

 versity in their dimensions; the smallest of them not weigh- 

 ing above 15 grs., and the largest a little above 400 grs. 

 The weight of all the crystals and fragments obtained, as 

 near as I can estimate them at present, did not exceed 12 

 or 1 400 grs. Not having until very lately, been able com- 

 pletely to verify my conjecture, concerning their nature, I 

 have withheld until the present moment all notice of the lo- 

 cality; which 1 now take much pleasure in making public, 

 totfether with a minute account of the steps followed in ar- 

 riving at the conclusions here announced. 



Mineralogical Description. 



Form. Right rectangular prism : the height of which may 

 be represented by 8, the length of the base by 6, and the 

 breadth by 4. The annexed figure, presents the most fre- 

 quent modification observed among these crystals. Their 

 angles are determined, by the common goniometer. 



F on M, or T 90°,00 



M on T 90 ,00 



Ton«' 133,00 



Mona' 116,00 



Tono 156,00 



