Page images




Dunnington' has pointed out a source of error to be guarded against in estimating titanium in rocks and minerals by Weller's method, due, as he believes, to the partial reversion, in certain cases, of ordinary titanic to meta-titanic acid, which does not afford a yellow color with hydrogen peroxide. It remains for me to indicate another source of error in the possible presence of fluorine in the hydrogen peroxide.

For two years the colorimetric method has given reasonable satisfaction in this laboratory, but recently a new lot of hydrogen peroxide was purchased of a different brand from that hitherto used, and after a time it was noticed that the results obtained were in some instances far too high, and that no two determinations agreed.

It is known that hydrogen peroxide does not produce a yellow color in titanium solutions carrying hydrofluoric acid or fluorides, and moreover the addition of even a drop of the dilute acid to an already peroxidized titanium solution weakens the color. For this reason it is necessary to take the greatest care to insure the complete expulsion of all fluorine when dissolving rocks or minerals by means of hydrofluoric and sulphuric acids prior to the colorimetric estimation. A drop of hydrofluosilicic acid acts similarly, but the latter reagent can not be made to completely discharge the color even if added in great excess.

This, however, was not suspected as the cause of our trouble until, on referring to the circular of one of the leading makers of hydrogen peroxide in this country, whose product has always given satisfactory results in titanium work, it was found that among the various acids enumerated as usually to be found in the commercial article, hydrofluroic acid appears. Talbot and Moody, in the Technology Quarterly, v. 123, mention hydrofluosilicic acid as of frequent occurrence in the peroxide manufactured a few years ago.

On examining the suspected peroxide by neutralizing with fixed alkali, evaporating to dryness, and heating with strong sulphuric acid, fluorine was detected by the odor of the acid evolved and by its action on glass.

It is therefore imperative to use only hydrogen peroxide which is free from fluorine in estimating titanium, for its presence may utterly vitiate the results, even if only 2 or 3 cubic centimeters of the peroxide are employed.

1 Jour. Am. Chem. Soc., Vol. XIII, p. 210.




The occurrence of tellurium in the ores of the mining district of Cripple Creek, Colorado, has been known from an early day in the as yet brief industrial history of that region. That it was, in part at least, associated with gold was likewise known from the observance of a crystallized gold-tellurium mineral. Although the ores of the district are chiefly gold carriers, they contain also a little silver, and since recognized silver minerals had not been observed, or at most only in minute amount, it seemed probable that the silver was associated with the gold in the tellurium compound. Indeed, Mr. R. Pearce, of Denver, came to the conclusion, from analyses of oxidized and unoxidized ores,' that this mineral was sylvanite, and he says: “Sylvanite itself appeared in little silver white specks disseminated through a mass of greenish rhyolite.” Notwithstanding that F. C. Knight? has identified calaverite by analysis and that sylvanite has not been identified by positive chemical and crystallographical tests, the evidence of Mr. Pearce as to its presence, in some portions of the district at least, is entitled to consideration.

The telluride examined by me was collected by R. A. F. Penrose, jr., who procured his material from three different mines in order to ascertain whether it was of constant or varying composition, or, in fact, whether there might not be more than one specific compound. That the composition does vary within narrow limits the analyses show; but there is no reason apparent for assuming the existence of more than one species in the ores of these particular mines.

The material from the Prince Albert mine, the first received, was with little trouble brought into an almost ideal condition of purity. It was in part apparently fairly well crystallized, but the measurements made by Prof. S. L. Penfield, of New Haven, are unfortunately not decisive as to the system of crystallization, as shown by his notes at the close of this paper. The specific gravity of this material was 8.91 at 24° C., which becomes 9 when corrected for a small admixture of silico-ferruginous gangue of assumed specific gravity 2.70 (probably

1 Proo. Colorado Sci. Soc., Vol. V, 1894, pp. 5, 11.

2 Ibid., Vol. V, 1894, p. 70.

low). The other samples were imperfectly crystallized and held too much foreign matter of uncertain composition to make specific gravity determinations of any value.

[blocks in formation]

a This was included with the insoluble matter in arriving at the corrected density.
6 Calculated from the Fe to make FeS2.
cAs MnO2?

d A part of the calcium found in solution was derived from fluorite, which likewise consti. tuted some of the insoluble matter in this instance.

Selenium has been reported in the oxidized ores of the district, but it could not be detected in the amount of mineral taken for the above analyses.

Excluding everything but gold, silver, and tellurium and recalculating to 100, the following comparison is obtained:

[blocks in formation]

The ratio here obtaining is that for sylvanite and calaverite, but the very low percentage of silver shows that the mineral is calaverite. Indeed the first analysis agrees almost exactly with Genth's analyses

1 F.C. Knight, Proc. Colorado Sci. Soo., Vol. V, 1804, p. 68.

of the species. Interesting is the slight variation in the ratio between gold and silver, and the very low percentage of silver in the mineral from the C. 0. D. and Raven mines. Calaverite, the lowest silver carrier of the gold-silver tellurides, has not heretofore been known to carry less than 3 per cent of silver.

The pyrognostic characteristics of the mineral from the Prince Albert mine were essentially those ascribed to calaverite. In the closed tube it fuses, giving a white coating near the assay, and a globular gray coating just above, which latter by strong heat can be in part driven higher up, leaving the glass covered with the same white fused coating as lower down. This latter is yellow while hot.

This latter is yellow while hot. On charcoal the mineral fuses with a green flaine, giving a white coating and similar fumes, and leaving a yellow bead. The color is pale bronzeyellow, in powder greenish gray. The hardness is not less than and perhaps a little over 3. Specific gravity, as given above, 9.

The identity of the telluride occurring at Cripple Creek, which in oxidizing gives free gold and oxidized tellurium compounds,' seems thus satisfactorily established, but unless there is another richer in silver, as believed by Pearce, the mode of occurrence of the silver in some of the ores is still in large part unaccounted for. It may be derived from a very rich argentiferous tetrahedrite of which Professor Penrose sub mitted a small specimen for identification. This carries over 11 per cent of silver, but is said to be excessively scarce and therefore hardly to be considered in this connection, unless indeed this should have been the original source of most of the silver and later have suffered oxidation to a great extent whereby the silver has become more evenly distributed throughout the ore.

Professor Penfield has kindly contributed the following notes on the crystallography of the mineral:

The crystals of calaverite which were examined were developed with prismatic habit, but the prismatic zone was striated to such an extent that it was impossible to identify a single face in the zone, and on the reflecting goniometer almost an unbroken band of signals was obtained in a revolution of 360°. Owing to oscillatory combinations the crystals were also much distorted, so that they did not present regular cross sections.

The prislns were attached so that doubly terminated ones were not observed, while the faces at the free end were small and developed with so little symmetry that after a study of a number of crystals it was found impossible to determine with certainty the system of crystallization,

The crystals do not exhibit the perfect cleavage ascribed to sylvanite and krennerite, but are similar to the former iu some of their angles. When placed in position to show their relation to sylvanite they have their prismatic development parallel to the b axis. One crystal, which owing to its development was more carefully measured than any of the others, was apparently a twin about 101, and showed

1 From tests made by myself on a number of specimens collected by Professor Penrose the combination seems to be chiefly if not altogether with iron, but whether as tellurite or tellurate could not be ascertained. Knight (loc. cit., p. 69), however, has shown that the combination, in some cases at least, is a tellurite, approximating to the formula 2(Fe,03, 2T002)+H30.

at the end the forms 111 and 110. The measurements compared with the corresponding ones of sylvanite are as follows:

Sylvanite. 111^(111) over twinning plane

93° 35' 94 30 110A(110) over twinning plane

35 2 34 43 110/111 .......

36 35 37 3 1101111 in twin crystal....

36 33 37 3 Other forms which were measured could not be referred to the sylvanite axes, and it seems probable from their development and lack of symmetry that the crystals are triclinic; but no satisfaction was obtained after a long and careful study of the limited supply of material on hand.

In conclusion therefore it may be stated that the crystals are probably triclinic, but near sylvanite in angles and axial ratio.

NOTE.-Since the foregoing work was completed additional analy. ses of Oripple Creek tellurides have been made by Profs. A. H. Chester and W. H. Hobbs.? From the crystallographic data they were able to obtain it would appear that neither of the minerals examined by them can be identical with calaverite, though both possess the same general formula MTez, in which, however, the ratio of gold to silver was not at all alike. The analysis of that one, which by its crystallographic features was identified as krennerite, has even less silver than the specimens of calaverite from the C. O. D. mine, while goldschmidtite, showing crystallographic relations with sylvanite, contains 8.95 per cent Ag to only 31.41 per cent Au, thus supporting, in a measure, Mr. Pearce's belief in the existence at Cripple Creek of a telluride much richer in silver than calaverite.


In a suite of tellurides from the Mother Lode region in California, collected by Mr. F. L. Ransome, of the United States Geological Survey, I have been able to identify a nickel telluride (melonite ?), a mercury telluride (coloradoite ?), besides petzite and bessite.


Several specimens from the old Stanislaus mine," the original source of Genth's melonite* (Ni, Tez?), but now included with the Melones and

"On krennerite from Cripple Creek, Colorado. Am. Jour. Sci., 4th series, Vol. V, 1898, p. 375. ? Goldschmidtite, a new mineral. Am. Jour. Sci., 4th series, Vol. VII, 1899, p. 357.

3 Mr. Ransome has kindly furnished the following notes: This mine is situated on the south slope of Carson Hill, Calaveras County, just above Robinsons Ferry, and has not been worked for several years. There is no prominent vein at this point, the ore being very irregularly distributed, and occurring in small, nearly horizontal, stringers in dark clay slates of Carboniferous age, with nearly vertical dip. This mine has long been known as a source of interesting tellurides, and Dana, in the sixth edition of his System of Mineralogy, cites petzite, calaverite, melonite, and altaite as occurring here. The other ore minerals are pyrite and galena, the latter in small quantities. The ore-bearing stringers are filled with quartz, or a mixture of quartz and calcite as a gangue. The rich masses of tellurides appear, however, to be usually associated with calcito (or dolomite). The melonite of specimen No. 16, shows at least one perfect cleavage, resembling in the thinness of the resulting lamine the cleavage of the micas. The cleavage faces are usually somewhat curved, and possess a splendent metallic luster. The cleavage can best be detected by carefully scraping thin folia from such a brilliant surface with a sharp knife point. The color of the cleavage faces is pale brunze yellow.

* Long o, accented (inel-y-nite).

« ՆախորդըՇարունակել »