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Neglecting the last three constituents in each case, the ratios become for Bastnäsite
R:F, CO3 =1:2.94
.R:F, CO3 = 1:3. 05 which ratio for tysonite is not changed by allowing for admixed bastnäsite.
The above direct fluorine determinations fully establish the hitherto assumed formulas R'' F3' for tysonite and R'" (FC0,'') for bastnäsite.
Early in 1896 Mr. George F. Kunz sent for examination a beautiful pale green mineral from Utah, supposed to be identical with the green variscite called by him utahlite in Mineral Resources of the United States, 1894, page 602. Under a recent date Mr. Kunz writes that Mr. T. H. Beck, of Provo, Utah, found the mineral “in 1895, in the Dugway mining district, Tooele County. It was found in a low range of hills about 5 miles long, surrounded by a desert on an arid region occurring as flat rock, associated with fluorite, native silver, slate, and trachytic rock (?), containing decomposed pyrite in which there was present a little free gold.”
Unexpectedly this was found to be the hydrous aluminum calcium fluoride prosopite, mixed with some quartz and probably tluorite, and colored by a small amount of some copper salt. A new and interesting occurrence for this very rare mineral is thus afforded.
The material as prepared for analysis after separation by a heavy solution proved to be still far from pure; quartz grains in amount from 1 to 2 per cent were left undissolved after complete conversion of the fluorides into sulphates, and presumably considerably more had been removed by the escaping fluorine. The total amount of quartz was not determined, and the material at hand did not suffice for attempts at more complete purification, so that the conclusions drawn from the analysis, while extremely probable, are not to be taken as altogether proven.
The specific gravity of the mineral as analyzed was 2.87 at 21° C. and the bardness about 4.5, both agreeing with the constants for prosopite. Furthermore, but little of the water (1.25 per cent) was expelled by several bours heating at 2800 C. Analysis gave:
Neglecting copper, alkalies, and the oxygen calculated for their oxides, and assuming the water to exist entirely as hydroxyl, the foilowing not very satisfactory atomic ratios result:
.7407 2 Ca...
. 3712 F.
1. 33541 Hydroxyl.
1.5808) if enough calcium and its equivalent in fluorine are subtracted to make the ratio Al : Ca exactly 2 : 1, on the not improbable assumption that fluorite is present as an admixture, an assumption that had to be made also for the Colorado prosopite in order to bring it into close agreement with Brandi's formula.
There is now a deficiency in the acidic radicals. The figures for Al, Ca, and H,0 are undoubtedly very nearly correct, while the fluorine may well be a half per cent low, having been determined by the Berzelian method, owing to the difficulty of securing complete decomposition of the fine powder by a single treatment with sulphuric acid. Let it be permitted to balance the basic and acidic radicals by raising the fluorine, and to figure the ideal percentages on this basis. These become of interest when compared with the corresponding figures for prosopite from Altenberg and Pikes Peak as given below:
If the assumptions made in the foregoing are justified, the Utah mineral is prosopite, and further evidence is arforded of the correctness of the view established by Penfield that fluorine and hydroxyl can mutually replace each other in many mineral species, for their relative proportions differ materially in the prosopite from the three known localities. The correctness of the formula as applied to the Colorado and Utah prosopite is, however, predicated, as said, on the unproven assumption that the material analyzed contains some admixed fluorite.
Two brown substances associated with franklinite and other zinc minerals from Franklin Furnace, New Jersey, so alike in appearance as to have been taken for the same mineral species, were received from Mr. George L. English. One was a little duller than the other and proved to be a mixture of several minerals, according to Mr. F.L. Ransome of the U. S. Geological Survey, largely pseudomorphic after some micaceous mineral. From Professor Clarke's calculations, based on the following analysis, it might be a mixture of a calcium-aluminum garnet, troostite, and limonite. Si0, 32.09, A1,0, 11.12, Fe2O3 5.16, MnO 15,85, ZnO 16.89, CaO 15.65, H,0 2.15, MgO and alk. 1.12; total 100.00.
The other was of a richer and deeper brown, and showed such a pronounced cleavage or parting in one direction as to produce a lamellar structure. The luster was brilliant on these cleavage surfaces. Other directions of cleavage were apparent. The hardness was about 5.5 and the density 3.39 at 21.5° C. Before the blowpipe a fragment fused with difficulty to a light-colored blebby glass. Analysis gave:
. 36 .37 7.43 3. 31 23. 68 12.57
Ti02, FeO, P205 absent.
Neglecting the sesquioxides, alkalies, and water, this leads to the ratio SiO2: RO=1: 1.02, and the formula is that of a metasilicate R'SiO3. According to Mr. Euglish, the material submitted by him had been pronounced by Professor Penfield on the basis of qualitative tests to be jeffersonite, a manganese-zinc pyroxene, a statement supported by the analysis above given, although neither the color of the mineral nor its quantitative composition agree with the hitherto published data. In Dana's Mineralogy the color is given as "greenish black, on the exposed surface chocolate brown," the density as 3.36 on page 358, but 3.63 on page 360. The discoverers of the species, Keating and Vanuxem, give 3.50-3.55 for the density and 4.5 for the hardness. The present mineral presents all the evidences of being fresh and unaltered, yet it is brown throughout, and its analysis furnishes figures widely at variance with those of Herrmann and of Pisani, but giving a better metasilicate ratio than either of their analyses. Notwithstanding these discrepancies, there is no reason for ascribing to the mineral a new subspecies name. The analysis is chiefly valuable as showing a wide range of composition for the mineral.
8. ANORTHITE AND EPIDOTE.
In specimens collected by T. F. Lamb at Phippsburg, Maine, these two iniuerals occur under unusual circumstances. The mass of the material is a highly metamorphosed contact limestone, carrying an abundance of cinnainon garnet and occasionally a green pyroxene. Now and then there is embedded in the masses of garnet a dark-gray mineral, nearly black in some specimens, in brilliant plates which nowise suggest epidote. Epidote, however, it proved to be, as shown by the subjoined partial analysis, and as verified by Mr. J. S. Diller under the microscope. The anorthite, also determined optically by Mr. Diller, and analytically by Mr. George Steiger, is associated sometimes with the epidote and sometimes in coarse crystals only with the garnet. The analyses are as follows:
In some ways the epidote resembles axinite, a mineral which has long been recorded as found at Phippsburg. Is the supposed axinite really epidote?
The rare mineral roscoelite has greatly needed reexamination, in order to reconcile the discrepancies between the analyses of Roscoe and Genth and to establish a satisfactory formula for this supposed vanadium mica. To the kindness of Mr. G. W. Kimble, of Placerville, California, I am indebted, through Mr. H.W.Turner, for specimens from the Stockslager mine, from which a limited amount of fairly pure material was picked out. This was then laboriously purified by the aid of Thoulet's solution, the result being a very nearly pure product weighing only 1.2 grams and having, after drying at 100° C., a density of 2.97 at 200 C.
Notwithstanding the small amount, it was possible by the exercise of care to make fairly satisfactory analyses.
With regard to the methods employed little need be said except as to the determination of the condition of the vanadium. For this purpose decomposition was effected by rather dilute H,SO, in sealed tubes, the greatest care being taken to expel every trace of air from the powder and acid, and to seal the tube during passage of a current of C02. Otherwise it is impossible to prevent oxidation of a considerable part