440 Pirsson and Washington — Geology of Red Hill, N. H. 



In No. I the ratio of Na„0 : Fe„0 3 : SiO„ = 1-03 : 1-00 :4'00 

 and of (FeO,MgO,CaO) : (SiO.TiO,) = 1-00:0-97. In No. II 

 Na s O : Fe 2 3 : Si0 2 = 0-99 : 1-00 : 4'00 and (FeO,CaO) : Si0 2 = 

 1*00: 1*02. These calculations are worth giving thus in detail 

 because the feldspars having been calculated out of the rock 

 exactly, all of the errors of the analyses fall on the oxides in 

 the amphiboles except silica, and the exactness of these ratios 

 is a proof of the correct composition of these amphiboles, and 

 is also a striking tribute to the remarkable accuracy of Wash- 

 ington's analysis. 



In the first the ratio of NaFeSi 2 6 : FeSi0 3 = 1:3 and in the 

 second 1 : 2.5. 



Washington states for the Quincy mineral that c on 6 = 4°- 

 7° and in paisanal liparose from Magnolia, Essex Co., Mass.,* 

 he mentions the same arrangement of the axes of elasticity. 

 Thus the present instance makes the third occurrence in the 

 Novanglian province of alkalic hornblende in which c lies 

 nearest to 6. Whitef on this account calls it a glaucophane, 

 and Washington to some extent follows him. Rosenbusch;}: 

 has shown, however, that the arrangement of the optical sys- 

 tem in the alkalic hornblendes is variable and it is best to 

 make the distinction between the glaucophanes and the arfved- 

 sonite-riebeckite series a purely chemical one, as he does. 

 The present mineral then, determined by its chemical composi- 

 tion, would be a riebeckite with bluish-green colors and 

 abnormal axial position. 



In connection with the greenish blue or bluish green color 

 of riebeckite it is of interest to note that it resembles Prussian 

 blue ; the latter is a ferrous ferricyanide, riebeckite is a ferrous 

 ferri-silicate. Yivianite, the hydrous ferrous phosphate, is 

 colorless when fresh, but on exposure and oxidation of a part 

 of the iron to the ferric condition it becomes a Prussian blue 

 color. There is evidently a connection in these substances 

 between this particular blue color and an arrangement of fer- 

 rous-ferric molecules. 



In places it is bleaching and altering to epidote. 



Of biotite only a few flakes were seen. Also a number of 

 small grains of zircon occur and minute grains of an unknown 

 mineral of high single and low double refraction. Titanite 

 was not observed. 



The feldspars are microperthit.es and the albite lamellae fre- 

 quently show the albite twinning. They are developed in the 

 larger crystals as short, thick, tabular on the a axis and attain 

 a length of 2 - mm . Further description of them is deferred 



* Jour, of Geol., vol. vii, p. 113, 1899. 



f Petrog. Boston Basin, Proc. Bos. Soc. Nat. Hist., vol. xxviii, p. 130, 1897. 



X Micro. Pkys. Min., vol. i, pt. 2, p. 247, 1905. 



