26o 



FRANK D. ADAMS 



No. 3 



No. 4 



No. 5 



No. 6 



SiO.,. 



TiOs. 



AI2O, 



FegO' 



FeO. 



MnO. 



MgO. 



CaO. 



NaoO 



Kgb. 



H,0. 



38.633 



5 • 035 



11.974 



3-903 

 "•523 



0.729 

 10.200 

 12.807 



3-139 

 1.489 

 0.330 



39-75 

 5.40 



15.00 

 7.86 

 2.89 



14. 16 



12.97 



1 .92 



1. 61 



40.15 

 5.21 



14-34 

 7.80 



4-53 



13-14 

 11.75 



2-31 

 1. 14 



40.14 

 4.26 



14-30 

 7.07 

 6.27 

 0.21 



II .62 



12.00 

 2 .22 

 1-35 



41-35 

 4-97 



13.48 

 5-14 



10.33 



11.44 



10.93 



2. 10 



0.62 



0.48 



39.16 



14-39 

 12.42 



5.85 

 1.50 

 10.52 

 II. 18 

 2.48 

 2.01 

 0-39 



99.762 



101.56 



100.37 



99-44 



100.84 



99.90 



No. I. Hornblende. From the essexite of Mount Johnson, province of 



Quebec, Canada. 

 No. 2. Hornblende. From Bohemian Mittelgebirge. 



No. 3. Hornblende. From tuff of hornblende basalt, Hartlingen, Nassau. 

 No. 4. Hornblende. Basalt tuff, Hoheberg, near Giessen. 

 No. 5. Hornblende. From "hornblende diabase," Graveneck, near Weilburg. 

 No. 6. Hornblende. Syntagmatite. Jan Mayen. 



Analyses Nos. 2 to 6 are taken from Schneider's paper referred to below. 



The hornblende thus belongs to the class of basaltic horn- 

 blendes, and not to the barkevikites as might be expected. It 

 contains, however, proportionally more of the iron in a ferrous 

 condition, together with somewhat less alumina and a somewhat 

 larger proportion of alkalies than most basaltic hornblendes. 

 The unusually high extinction for a hornblende of this class 

 which it possesses is probably connected with the high content 

 in ferrous iron, since Schneider ^ has shown that the extinction 

 increases with the increase of iron in this state of oxidation. 



Pyroxene. — This mineral occurs intimately associated and 

 often intergrown with the hornblende, both minerals frequently 

 holding many inclusions of magnetite and apatite. It is very 

 pale-greenish in color, with no perceptible pleochroism, but with 

 a marked dispersion of the bisectrices. It is usually hypidio- 

 morphic, but is frequently idiomorphic, showing a distinct cleav- 

 age parallel to the pinacoids, but usually none parallel to the 

 prismatic faces. It belongs to the variety of diopside-like 



' "Zur Kenntniss basaltischer Hornblenden," Zeitsch?-. fiir Kryst., 1891, p. 579. 



