ART. XIV.—A Remarkable Nugget of Platinum; by PETER COLLIER, of Washington, D. C. 1888
SEVERAL years ago I came into possession of a nugget of platinum, said to have been found upon land adjacent to the village of Pittsburgh, New York. Upon examination, the nugget was found to be composed entirely of native platinum ana chromite disseminated through it. This chromite was black and of a somewhat resinous luster. The dimensions of the nugget were: length 4 cm., width 3 cm., thickness 26 cm. Its weight was 1044 grams. The specific gravity of the entire nugget was 10'446, and an average of three determinations with a pycnometer of small fragments of the native platinum gave 17'35 as their specific gravity.
This indicates the composition of the nugget by weight to "be about as follows: chromite 54 per cent, native platinum 46 per cent The nugget was found to be slightly attracted by the magnet, a fragment weighing -09 gram being raised by the magnet. The metallic portion, separated as completely as possible from adhering chromite, was dissolved in aqu? regia, leaving a slight residue, which was mainly chromite and sand, of only -74 per cent. The chromite was decomposed by fusion with bisulphatc of potassium. Its composition is given as iollows;
There appeared in the interstices of the mass a little earth which probably accounts for the above results of analysis. By deducting these impurities the above analysis would be:
Owing to the small quantity of the mineral taken for analysis, 1'45 grama, and the diffiy in separation, the above analysis is perhaps not rigidly exact, and in fact the presence of
mined. The above analysis, however, shows conclusively that-the specimen is a genuine nugget of native platinum ; and upon an investigation of the person who found the same, it-seems established beyond question that his statement is correct, aioce the mode of its occurrence and the locality is such as tcr render the statement quite credible.
Several other specimens were said to have been found at the time when this was discovered, but owing to their real value being unknown they were mislaid or lost. A personal examination of the locality shows it to be in a drift deposit which is of considerable extent Adjacent rocks exposed upon the surface show well-defined glacial scratches, and the bowlders constituting this deposit are mainly from rock not present in place in that immediate locality. The occurrence of the plaii. num metals in the St. Lawrence valley has long been known, and the presence of extensive deposits of cliromite and its mineral-associate, serpentine, in the same general locality is well established, but so far as I can learn this nugget appears to be remarkable not only for its size, but also an indication of the probable presence of this metal in a locality hitherto unsuspected.
The glacial striations near Platteburg have been reported by H. P. Gushing to run from S. 18? E. to 8. 15? W. and to be influenced by (.he local topography. Farther south the writer has noted them in the valley of the lake, as well as back in the mountains, to lie S.W. /N.E. as a rule. A southwesterly movement of the iee sheet would have brought glacial mattrial to Plattsburg from the great areas of serpentine which occur in Quebec north of Vermont and which are commercially productive of chromite. There seems little reason, therefore, to doubt that the nugget has been derived from this source, but as yet no platinum lias been announced in the serpentine region.
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