Augite from Vesuvius and Etna. 29 



The specific gravity of the crystal fragments used for 

 the analysis, determined with a pycnometer, was 3.373 

 referred to water at 22"^. 



Chemical composition. — The loose crystals appear to 

 be very pure, except for patches of a siliceous material 

 (which was readily removed by dilute hydrofluoric acid). 

 Small grains of yellow olivine project from the surfaces, 

 but they are not found in the interior of the crystals. 

 After crushing a batch of crystals to small fragments for 

 analysis, all these olivine particles were carefully 

 removed by repeated search under a binocular, and the 

 material used for analysis is confidently believed to have 

 been free from them. The crystals, however, contain a 

 small amount of minute inclusions of magnetite, which it 

 was impracticable to remove entirely. Treatment with 

 a magnet of about 0.6 g. of the powder analyzed showed 

 that this was present to the extent of 3.94 per cent, and 

 in column 2 of Table II the analysis is corrected for 4 

 per cent of magnetite. 



TABLE II. 



12 3 4 



SiO., 47.89 50.09 47.63 47.38 



Al,6; 3.55 3.71 6.74 5.52 



FeA • 4.17 1.47 n.d. 5.52 



Feb 5.98 4.96 11.39 7.89 



MgO 13.40 14.01 12.90 15.26 



CaO 21.49 22.48 20.87 19.10 



Na.,0 0.70 0.73 n.d. n.d. 



K,6 0.01 0.01 n.d. n.d. 



H..0+ 0.21 0.22 0.29 0.43 



TiO., 2.02 2.11 n.d. n.d. 



MnO 0.20 0.21 0.21 0.10 



99.62 100.00 100.03 99.53 



Sp.gr 3.373 2.886 2.935 



1. Augite, Monti Eossi, Etna. Washington analyst. 



2. Same, corrected for 4 per cent of magnetite. 



3. Augite, Monti Eossi, Etna. 8. van Waltershausen analyst. Der Etna, 



2, 490, 1880. (First published in 1853). 



4. Augite, Monti Eossi, Etna. Eammelsberg analyst. Pogg. Ann., 103, 



436, 1858. 



Only ^Ye or six published analyses of these augites are 

 to be found, and all suffer from. the same defects that 

 were pointed out in the case of the Vesuvian augite, that 

 is, non-determination of titanium and alkalies, and, in 

 many, non-separation of the iron oxides. 



Discussion. — Any extended discussion of my analysis 

 is unnecessary here, and will be reserved for a future 



