Vol. 4] Murgoci. — Classification of the AmpJtiboles. 



365 



uniaxial, occur frequently in the glaucophane schists of Califor- 

 nia, and some are faintly colored. Unfortunately there are no 

 analyses of these varieties to show us precisely in what the chem- 

 ical variation may consist. We can discuss the question from 

 the chemical point of view better after the consideration of the 

 next minerals. 



The constitution of the uniaxial glaucophane is that of a glau- 

 cophane with Al :Fe = 3 :1, viz. : 



{ Na 2 Si0 3 

 | FeSiO a 



\ 2MgSiO s Mg:Ca = 6:l Al:Pe = 3:l 



| (Fe'"Al) = Si 3 3 

 I H 2 Si0 3 



Crossite. — Charles Palache gave the name of crossite to a 

 blue amphibole-like glaucophane, which occurs in an albite schist 

 in the hills near Berkeley.* The chief property of crossite, which 

 on the original section I have determined independently of for- 

 mer observations, had been remarked already some ten years ago 

 by Dr. A. C. Lane, but has never been published. In the last 

 edition (IV) of Mikroskopische Physiographie I, Bd. II, Halfte, 

 H. Eosenbuseh gives almost the same properties determined on 

 specimens presented by Palache. My determinations were made 

 on the original sections just at the time of the publication of that 

 book and were communicated to Professor Eosenbuseh in a let- 

 ter.f Later I had the opportunity of finding this interesting 

 mineral in several rocks of the Coast Eanges of California, some- 

 times with characters even more distinct than in the original 

 sections. (See the material studied.) 



The properties of crossite are so important for the general 

 question of the amphiboles that I shall give more details here. 



The chief property of crossite is that the plane of the optic 

 axes is perpendicular to the plane of symmetry, the optic normal 

 making an angle of -16° with the vertical c' axis. Accordingly 

 the pleochroism, which is identical in its colors and crystallo- 

 graphic orientation with that of glaucophane, is: a = brilliant 

 yellow, 6 ~ dark Prussian blue, C = dark violet. Very strong 

 absorption, C = fa> a, sometimes b > C, and almost opaque. 



* C. Palache. On a new Soda Amphibole, etc. Bull. Dept. Geol. Univ. 

 Cal., 1. p. 181. 



t Eosenbuseh 's observation, loc. cit., p. 246-247; my communication, p. 395. 



