J. H. Pratt — Miner alogical Notes. 



431 



Enstatite {Bronzite). — The occurrence of a bronzite diopside 

 rock (websterite) in the midst of an outcrop of dunite, near 

 Webster, Jackson County, N. C, has been described by 

 Williams* and Lewis.f Near the western border of this out- 

 crop bowlders were observed that were composed almost 

 entirely of bronzite. 



The mineral is of a resinous brown color and of a bronze- 

 like luster even on the unaltered surfaces. No distinct crystals 

 were observed, the specimens being a mass of interlocking 

 crystals making a very tough rock similar to the enstatite 

 described above. The material for analysis was carefully 

 selected by hand picking, and showed no impurities or decom- 

 position when examined with the magnifying glass. The 

 analysis of this mineral by Dr. Baskerville is given below : 



Si0 2 53-62 



A1,0," -97 



Cr s O, '50 



FeO _.. 9-06 



CaO 1-75 



MgO 33-53 



HO 19 



•012 



Ratio. 

 •894 

 •009 

 •003 

 •125 



•03i y 



•838 

 •001 



r 



i-ii 



99-62 



In the above analysis the ratio of the bivalent oxides to 

 silica is close to 1 : 1 and of ferrous oxide to magnesia and 

 lime is very near to 1 : 7 ; this would give the formula (MgFe) 

 SiO, with Mg:Fe = 7:l. 



Assuming that the A1 2 3 and Cr 2 3 belong to spinel, and 

 deducting RO sufficient to combine with them, the analysis, 

 after substituting for CaO its equivalent of MgO and recalcu- 

 lating to 100 per cent, is given below, together with the theo- 

 retical composition. 



Theory for 

 Found. (Mg,Fe)Si0 3 ; Mg : Fe = 7 : 1. 



Si0 2 55-35 57*69 



FeO 9-14 8-65 



MgO 35-51 33-66 



100-00 100-00 



The name bronzite is very appropriate for this Webster 

 enstatite, as the luster is of a decided bronzite-like character 

 throughout the entire mass, and it is undoubtedly not of sec- 

 ondary origin. A similar bronzite has been found at the Buck 

 Creek, Cullakeenee, corundum mine in Clay County. 



* American Geologist, vi, pp. 43-4, 1890. 

 f N. C. Geological Survey, Bull. 11, p. 27. 



Am. Jour. Sci.— Fourth Series, Vol. V, No. 30.— June, 1898. 

 29 



