LARSEN AND STEIGER: MINERALOGIC NOTES 11 



mentioned, is made up largely of the chlorite of that vein but 

 contains some quartz, some chalky decomposed rhyolite, and a 

 few flakes of sericite. 



The three analyses of thuringite are very much alike, but the 

 Creede mineral is lower in ferrous oxide and correspondingly 

 higher in magnesia and manganous oxide; its somewhat higher 

 content of silica may be due to admixed quartz. 



III. GRIFFITHITE, A NEW MEMBER OF THE CHLORITE GROUP 



Introduction. The authors have hesitated before proposing 

 a new name for a member of the chlorite group, already over- 

 burdened with names that have little significance and less place 

 in a systematic scheme of classification. However, a chloritic 

 mineral filling amygdaloidal cavities in a basalt collected by 

 Mr. R. T. Hill from Cahuenga Pass, Griffith Park, Los Angeles, 

 California, differs so greatly, both optically and chemically, 

 from any of the chlorites previously described as to require a 

 new name, and the name griffithite, from the locality, is pro- 

 posed for the mineral. The amygdules of the basalt are up to 

 an inch in largest dimension and comprise a considerable part 

 of the rock; they are pure griffithite. 



Physical properties. The griffithite is dark-green in color, 

 it has a hardness of about 1, is sectile, and has a specific gravity, 

 as measured by the picnometer method, of 2.309. It is in basal 

 plates and shreds, and some of the plates are a millimeter across. 

 It has the usual cleavage of the chlorites. It fuses at about 4 

 with intumescence to a black magnetic slag. 



Optical properties. It is optically negative and 2V varies from 

 0° to 40°; X is normal to the cleavage. It has a strong bire- 

 fringence and a rather strong pleochroism. The indices of 

 refraction differ in different grains as much as 0.01; they and 

 the pleochroism are: 



a = 1.485 ± 0.01; pale yellowish, 

 = 1.569 ± 0.005; olive-green, 

 y = 1.572 ± 0.005; brownish green. 



