G. A. Ingersoll — HemimorjpTiio Wulfenite Crystals. 193 



apophyllite may be generated artificially from okenite, and 

 gyrolite occurs in nature both as the parent and as a derivative 

 of apophyllite. At New Almaden, apophyllite is the second- 

 ary mineral; while in Nova Scotia gyrolite appears to be 

 formed by its alteration. All three species, considered as 

 analogous in structure, are most simply represented as salts 

 of the acid H 6 Si 2 7 , and on this supposition they receive the 

 following formulae : 



Okenite. Gyrolite. Apophyllite. 



Ca /Si 2 7 .H 6 c /Si 2 7 .CaH 3 Ca /Si 2 7 - H 4 (CaOH) 



j>Si 2 7 . CaH, ^Si 2 7 . H 4 ^>Si 2 7 . H 4 



Ca \Si 2 7 . H 6 Ca \Si 2 7 . CaH s Ca \Si 2 7 . H 4 (CaOH) 



In apophyllite, the univalent — Ca— OH is partly replaced 

 by potassium, and the hydroxyl is often substituted by fluorine. 

 The somewhat uncertain plombierite may also be represented 

 as a memher of the same group, having the formula Ca 2 (Si o 7 ) 3 

 Ca 3 H 8 . 9H 2 0. 



Since the object of this paper is merely to give a prelimi- 

 nary statement of the conclusions which I have reached, I have 

 not thought it necessary to load down its pages with references 

 to literature or with discussions of analyses. A large mass of 

 data has been examined, and it is my intention to elaborate the 

 subject to a considerable extent within the near future. When 

 that is done the evidence will be presented with sufficient 

 fulness. 



U. S. Geol. Survey, Washington, June 20, 1894. 



Art. XXYII.-^tM IIemimo?yjuic Wulfenite Crystals from 

 JVeiv Mexico ; by Charles A. Ingersoll. 



The crystals that will be described in this communication 

 were found by Mr. William E. Hidden* at the Turquoise 

 mines in the Jarilla Mountains, Dona Ana County, New 

 Mexico, and were sent to Professor S. L. Penfielcl in the fall of 

 1892. They were implanted upon a brown siliceous gangue and 

 were described by Mr. Hidden as occurring in seams in trachyte, 

 associated with quartz, pyrite, chalcopyrite, malachite, gypsum, 

 jarosite and kaolin. They were said to be of quite rare occur- 

 rence, only a very few having thus far been found, and are of 

 especial interest on account of their peculiar hemimorphic and 

 pyramidally hemihedral development. 



*This Journal, IIT, xlvi, p. 401, 1893. 



