FENNER, THE WATCH UN G BASALT 147 



include the amphiboles, but it may be inferred that somewhat analogous 

 relations hold. It seems most probable that the amphiboles consist of a 

 series of metasilicates which are capable of imiting among themselves in 

 compounds of definite composition and in mixed crystals (solid solutions) 

 of variable composition. In such complex solid solutions as are formed 

 by associations of various members of the series, equilibrium with the 

 liquid with which the crystals are in contact is necessarily easily dis- 

 placed by changes in the composition of the liquid, and periiaps also by 

 changes of temperature. The metamorphoses which the amphiboles of 

 the Watchung rocks are found to have experienced are in harmony with 

 this conception and would be expected from the conditions to which they 

 were subjected. 



Somewhat similar phenomena to those described are mentioned by J. P. 

 Iddings :*^ 



Common hornblende and basaltic hornblende in some instances alter by the 

 loss of color and subsequent passage into pale or colorless amphibole, re- 

 sembling actinolite and tremolite ; often becoming -recrystallized as acicular or 

 fibrous aggregates (strahlstein). . . . 



The chemically simpler varieties, like tremolite and actinolite, are more 

 stable than the more complex hornblendes. In fact, the former frequently 

 result from the breaking-down of the more complex amphiboles. 



Regarding relative stability, however, the present writer would adopt a 

 somewhat different form of expression. The more complex hornblendes 

 are probably perfectly stable under the conditions of deposition, but with 

 a change of external conditions they tend to change in accordance. 



In the study of the transformation of labradorite into albite, it was 

 found that the original crystals gave up to the liquid that constituent 

 which was in excess and received that which was deficient, but with the 

 amphiboles it appears that the process which prevailed was a breaking-up 

 and solution of old crystals and deposition of new. 



Specularite (Specular Hematite) 



Specularite is seldom present in large quantity, but a small amount is 

 often found. It has been observed without the microscope in dark blade- 

 like crystals or groups or as a bright crimson or iridescent purplish dust 

 on faces and as inclusions in crystals of almost every mineral in the series. 

 The magnetite of the original rock appears to have broken up almost as 

 soon as recrystallization began, and its place was taken by hematite. In 

 slide 53, it is found in tabular crystals, reddish-brown by transmitted, 



" "Rock Minerals," p. 340. 



