THE DIABASES 



83 



Chemical Composition of Diabase and Basalt 



Constituents. 



I 



n 



Hi 



lY 



V 



VI 



Silica (SiOa) . . . 

 Alumina (AI2O3) . 

 Ferric iron (FesOg) . 

 Ferrous iron (FeO) . 

 Lime (CaO) • . . 

 Magnesia (MgO) . 

 Potash (K2O). . . 

 Soda (NagO) . . . 

 Ignition .... 



63,13^ 

 13.74 

 1.08 

 ; 9.10 

 9.47 

 8.68 

 1.03 

 2.30 

 0.90 



45.46% 

 19.94 



} 15.36 



8.32 

 2.95 



3.21 

 2,12 

 2.30 . 



56.52% 

 13.53 



12.56 



5.31 

 2.79 

 3,59 

 3,71 

 0.81 



61,02% 

 18.36 

 r6.57 

 14.68 



7.36 



6.57 



2.10 



2,54 



2.86 



57.25% 

 16.45 



1.67 



4.72 



7.65 



6.74 



1.57 



3,00 



0.40 



46,90% 

 10.17 



1.22 



6.17 



6.20 

 20.98 



2.04 



1.16 



5.42 



Specific gravity . . 



99.33^ 

 2.96 



99.66% 

 2.945 



98.82% 



• • « • 



101.56% 



• • * • 



100.35% 



99.26% 

 2.86 



I. Diabase: Jersey City, New Jersey (G-. W. Hawes). II. Diabase: Pal- 

 mer Hill, Au Sable Forks, New York (J. F. Kemp). III. Melapbyr: 

 Hoekenberg, Silesia. IV. Melaphyr, Falgendorf, Bohemia (quoted from 

 ZirkePs Lehrbuch der PetrograpMe). Y. Quartz basalt: Snag Lake, Cali- 

 fornia (J, S. Diller). VI. Basalt (absarokite) : near Bozeman, Montana 

 (G. P. Merrill). 



augite may become conyerted into hornblende, as already de- 

 scribed (p. 36), and the rock pass over into diorite. The plagio- 



clase may be oligoelase, 

 labradorite, or anortbite. 

 Structure. — In struc- 

 ture the diabases are holo- 

 crystalline. Earely do 

 the constituents possess 

 perfect crystal outlines, 

 but are more or less im- 

 perfect and distorted, 

 owing to mutual inter- 

 ference in process of for- 

 mation, the granular 

 hypidiomorpkic structure 

 of Professor Eosenbusch. 

 The augite in the typical 



Fig. 4.^Mierostructure of diabase. *^™S ^^^^^^ ^^ ^^^^^ ^^^ 



sharply angular plates en- 

 closing the elongated or lath-shaped crystal of plagioclase, giving 



