398 6*. L. Penfield — Mineralogical Notes. 



which the CI and F are isomorphous. Disregarding the small 

 amounts of P 2 B , CaO . Na 2 and Fe 2 3 the ratio of Si0 3 : 

 A1„0 3 : (CI . F.OH) is nearly 3:4:12, which is required by the 

 formula suggested by Professor P. Groth* [Al(Cl.F.OH) s ], 

 Al 2 Si 3 12 . The agreement between the author's and Mr. Hille- 

 brand's analyses is very satisfactory. Especially the percent- 

 ages of CI, F and hydroxyl, which are regarded as isomorph- 

 ous, are very close and yet there seems to be no definite pro- 

 portion in which these constituents are related to one another. 

 The relation of Cl + F : OH in the author's analysis is -380 : 1-236 

 or 1 : 3-25. 



Besides the occurrence of zunyite in the rock, as just de- 

 scribed, it also occurs at this same mine in a pulverulent form. 

 This material resembles some kinds of kaolin, is pure white 

 and consists of minute crystals, so loosely aggregated that they 

 can be disintegrated by rubbing between the fingers. Other 

 minerals found at the mine are enargite, pyrite, scorodite and 

 sulphur. The latter in small but highly modified crystals 

 showing the faces, 100, i-i; 010, «4; 110,7"; 101,14; 103, -J4; 

 011, 14; 111, 1 ; 113, i; 115, \ and 133, 1-3. The scorodite 

 was determined by proving it to be a hydrous ferric arseniate 

 of specific gravity 3 - 209. It is not crystallized but has formed 

 as a green, botryoidal incrustation on the enargite and decom- 

 posed rock. 



The author also visited the Zuili mine near Silverton where 

 the zunyite occurs intimately mixed with the sulpharsenite of 

 lead, guitermanite, and an earthy decomposition product con- 

 taining lead sulphate, as described by Mr. Hillebrand. Some 

 crystals were also found in the wall rock, which, like that from 

 Red Mountain, is a decomposed porphyrite. At both localities 

 zunyite is plainly a secondary mineral and has probably been 

 formed by fumerole action upon the silicates of the rock. 



The author takes pleasure in expressing to Mr. C. A. Taylor 

 of Red Mountain, and to Mr. R. H. Williams of Silverton, the 

 discoverer and owner of the Zuni mine, his obligations for 

 their kindness in supplying him with specimens and infor- 

 mation. 



2. JCenotime from Cheyenne Mountain, El Paso Co., Colorado. 



The occurrence of this mineral from the tysonite and bast- 

 naesite locality of El Paso County has already been noted by 

 Mr. W. E. Hidden. f His description was confined to a single 

 crystal, measuring over one centimeter in diameter, weighing 

 5*1 grams and which had suffered some superficial alteration. 

 The crystal to be described in the present article was given to 



* Tabellarische Uebersicht der Mineralien, 1889, p. 104. 

 f This Journal, xxix, p. 249, 1885. 



