Bl.ASDALE.] 



Contribution to Mineralogy. 



335 



R' 9 .«, and the second as R 2l . u X 12 . 5 R'i . 6 i- The 

 composition of the two samples may then be represented thus: — 



I II 

 2.36 R" 2 X. 2 R' 4 \ R// v R/ 2.65 R"X,R'a _ R „ x R , 



4.03 r"JxJ } =R X ' 2 ' 80 R 3.90 R' 4 X, ; - R »•« *»•» K 



Finally it may be stated that in crystallization, in optical and 

 in other physical properties, the mineral presents no remarkable 

 features, and its differences of chemical composition are not 

 sufficient to warrant separation from the mineral actinolite. 



A BLUE HORNBLENDE. 



Hornblendes of a deep blue color are not uncommon in the 

 rocks of the Coast Ranges. One of these was considered by 

 Lacroix* and later by Becker t to be normal glaucophane; a 

 second, the only one fully described up to the present time, was 

 shown by Palache to be identical with a species from Custer 

 County, Colorado, and was named by him crossite. The material 

 used by Palache was obtained from a locality but a few miles to 

 the north of Berkeley, about midway between the two localities 

 here considered, but, as the sequel shows, differs from the mineral 

 here described. 



Occurrence. — Unlike the actinolite, the blue hornblende is found 

 in rock masses of considerable extent, which must be regarded 

 as one of the important rock formations of this range of hills. 

 Good exposures are not plentiful, but their extent and the variety 

 of facies they present is evinced by the abundance of float strewn 

 over certain areas of the hill slopes. This material often assumes 

 the form of boulders, not dissimilar to those of the actinolite, but 

 commonly consists of more or less angular masses, most of which 

 show a schistose structure. Many specimens consist wholly of the 

 pure mineral, the crystals varying greatly in size in different speci- 

 mens, and the whole forming an exceedingly hard, compact mass. 

 Other specimens show mixtures of the mineral with albite, chlorite, 

 garnet, or actinolite, mica, and quartz. One large detached rock 



* Report Cal. State Mineralogist (1884), p. 182. 

 t Monograph XIII, U. S. Geol. Survey, p. 76. 



