Gen th and Vom Rath.] iiiA [April]?, 



"j'ai fait un essai preliminaire et 1g hasard m'afait detacliernn angle cl'un 

 "petit crista! passablenient translucide. II portait 2 faces m et 2 faces 

 "o(b^). De la patience, un pen d'adresse et beaucoup de bonheur m'ont 

 "permis d'arriver a una lame tres sensiblement parallele aux 2 aretes 

 "m : o, et passablenient transparente, lorsqu'elle a ele ties amincie. La 

 "masse est peu homogene comme dans les lames extraites des cristaux de 

 " Cdrdoba et une bande noir opaque la traverse en son milieu. II n'y a 

 ''done rien d'elonnant a ce que les analyses faitesjusqu'ici oflfrent des 

 "differences dans les proportions de zinc, de manganese ou de cuivre. 

 "Plan des axes parallele a la petite diagonale etbissectricene(7a<i«enormale 

 "a la lame et par consequant parallele a I'axe verticale ; malheureusenient 

 "les coles du triangle (de la lame) n'ont guere que f""", mais il y a bien 

 "d'esperer que quand on pourra sacrifier sans regret un ou deux gros 

 " cristaux pour les reduire en plaques excessiment minces, on arrivera a 

 "voir les anneaux dans I'huile, et par suite a s'assurer quel genre de dis- 

 "persion ils piesentent.' " 



From the foregoing it has been observed that the descloizite of the Sierra 

 Grande occurs in several varieties. In the first place there are : 



a. Minute crystals from microscopic to about 1™™ in size, often sharply 

 defined, varying in color, rarely orange-yellow, mostly from columbine- 

 red to cherry-red and reddish-brown to pale clove-brown. Powder pale 

 orange-yellow with a slight brownish tint. The crystals are isolated, but 

 generally united in groups, sometimes forming incrustations, and are asso- 

 ciated with calcite, quartz, iodyrite, vanadinite, pyrolusite and psilome- 

 lane, sometimes completely incrusted by the latter. Decrepitates on 

 ignition and fuses to a grayish-black mass. This variety is represented by 

 Fig. 2, and its composition is given in analysis a, 1, 2 and 3. 



b. The other variety. Fig. 3 and 4, is found in larger crystals, some of 

 which reach 8™" in size. They are brownish-black or black, either opaque 

 or, in transmitted light, of a reddish-brown color. Powder blackish-gray 

 with a yellow tint. Decrepitates on ignition and fuses to a black slag. 



As a rule, these crystals are very impure, being frequently penetrated by 

 a large admixture of pyrolusite which, on dissolving in dilute nitric acid, 

 remains behind. 



These dark crystals appear to be the oldest of the vanadates, found at 

 Lake Vallej'. They crystallize upon quartz and are associated with vana- 

 dinite, iodyrite, descloizite of a more recent origin, pyrolusite, psilomelane 

 and calcite. 



Analyses : 



a. Bed crystals. 



al. For a preliminary analysis 0.4769 grm red crystals, slightly coated 

 with pyrolusite, was used. They gave 0.0630 grm pyrolusite and quartz 

 which, deducted from the above, left 0.4139 grm pure descloizite which 

 gave : 0.3140 grm PbSO^, 0.0048 grm CuO, 0.0704 grm ZnO, 0.0082 grm 

 Mn^Ot and 0.0873 grm VjOj. 



