Page images
PDF
EPUB

expected. The plain in which it is found is a deposit of drift; a valley filled up with the debris of the neighboring mountains, consolidated by lime in which I found no fossils.

The meerschaum is found in this drift in masses more or less rounded; the other pebbles are fragments of magnesian and hornblende rocks.

I have examined with care the neighboring mountains which surround the plain, and have found that the rocks are of the same nature as the pebbles in the plain, except those of the meerschaum; but on the other hand I found carbonate of magnesia in the mountains which is not to be found in the plains. And this makes me suppose that the meerschaum owes its origin to the carbonate of magnesia of the mountains decom posed after its separation by water containing silica.

If this supposition be true we should naturally find meerschaum which not being completely altered contains the carbonate of magnesia. A chemical examination of several specimens has served to establish this fact. Some of the specimens, taken at the depth of ten feet, when placed in hydrochloric acid, give rise to an effervescence that will continue for some time; the piece will not change its form, it only absorbs the acid; the solution will be found to contain chloride of magnesium nearly pure. Another proof that the meerschaum probably owes its origin to the carbonate of magnesia is that I have found attached to the meerschaum serpentine similar to that found in contact with the carbonate of magnesia of the mountains.

The meerschaum of Eski-Shehr differs completely from several other specimens that I have seen, coming from other localities, and which exist in the fissures of rocks; it is certain that the quality of the first is most esteemed.

LESLEYITE OF CHESTER COUNTY, PENN.

AND ITS RELATIONS TO THE EPHESITE OF THE EMERY FORMATION NEAR EPHESUS, ASIA MINOR.

Several years ago a small amount of mineral from Chester County, Penn., was handed to me for examination by Dr. Isaac Lea, of Philadelphia. The specimen was too impure to warrant any conclusion upon analysis. Its character and associates, however, led me to suppose that it was the same mineral described by me as associated with the emery of Asia Minor, and to which I gave the name Ephesite. In the mean time Dr. Lea described his mineral as a new species, calling it Lesleyite; and in a recent number of the American Journal of Science and Arts, S. P. Sharples has given an analysis of it that at once brought to my recollection my original opinion that it was close to Ephesite, and on recurring to my examination of this mineral, making due allowance for the impurities contained in it, the opinion was confirmed.

I then obtained from Dr. Lea another specimen of his mineral, and proceeded to analyze both it and the Ephesite for mutual comparison. Much labor was bestowed in selecting the pure mineral from each, the greater part of a day having been consumed in procuring the necessary quantity for analysis. They are similar in their associations and identical in color and luster and general physical properties. They are both very difficult to decompose by carbonate of soda, even when aided with caustic potash; so that in both analyses the silica obtained was fused a second time, and much alumina separated from it.

My original description of the mineral will be found under Emery, in the American Journal of Science and Arts, 2d series, vol. x, 1850, as follows:

"It is of a pearly-white color, and lamellar in structure; cleavage difficult. It scratches glass easily, and has a specific gravity of from 3.15 to 3.20.

Heated before the blowpipe, it becomes milk white but does not fuse. At first sight it might be taken for white disthene. It is decomposed with great difficulty by carbonate of soda, even with the addition of a little caustic soda."

The lesleyite has identically the same properties. On analysis the two minerals were found to be composed as follows:

[blocks in formation]

The alkalies in the two varieties are reversed, the Ephesite containing principally soda and the Lesleyite potash.

This close relation of the two minerals is an interesting fact as regards the associate minerals of corundum found in different parts of the world.

In regard to the reddish variety of Lesleyite examined by Roepper, the analysis can not be considered as giving very satisfactory results, for the mineral may have been impure, and the difficulty in decomposing by the soda fusion may give very erroneous results in a silica determination.

13

TETRAHEDRITE, TENNANTITE, AND NACRITE,

OF THE KELLOGG MINES OF ARKANSAS.

A short time since Prof. E. T. Cox, of Indiana, sent to me an antimonial copper-ore containing silver, one fragment being the termination of a crystal having a number of small but beautiful faces; another was a minute crystal of a different form. In the hands of Prof. Cox a blowpipe analysis had given about five per cent. of silver in some of the mineral.

The crystalline fragments were first examined, and they enabled me clearly to trace out tetrahedrite in one and tennantite in the other. The faces on the tetrahedrite were small, but beautiful and very numerous; from the number on the fragment examined there would not have been less than from sixty to seventy had the crystal been perfect. It corresponds very nearly to the crystal figured in Dufrenoy's Mineralogy, plate 124, fig. 441, which he speaks of as coming from Moschellandsberg, a locality that I am not able to discover. Good measurements were made on a few of the faces.

P on P 70°: P on b3 159° 30'; P on a2 144° 30′.

Specific gravity of different specimens varied from 4.78 to 5.08; the latter was the specific gravity of the above crystal. The analysis of two specimens, No. 2 being a part of the crystal, gave

Antimony.

Sulphur..

Copper

Iron....

Zinc

Silver

Arsenic

1

2

[blocks in formation]

The quantity of No. 2 analyzed did not exceed three hundred milligrammes.

There are two minerals, consisting of minute micaceous scales, on the quartz containing this gray copper. One of them

I could not obtain in sufficient quantity for examination; from an imperfect examination I conclude that it is muscovite. The other mineral-a soft, unctuous, talc-like mineral-is nacrite, composed as follows:

[blocks in formation]

These minerals came from an exceedingly interesting mine in Arkansas that is as yet almost unexplored. I have obtained a description of it from Professor Cox, and I think it would be well to give it here; for, besides being likely to prove of considerable commercial value when properly explored, there will doubtless be found many interesting mineral species there.

The Kellogg mines are situated ten miles north of the city of Little Rock, in Pulaski County, Ark. The country in the vicinity is rolling; the highest hills are about two hundred and seventy feet above the water-level of the neighboring streams. The surface rocks are thick, and thin beds of sandstone alternating with shales occupying the base of the coal measures. The rocks are but little disturbed, and are for the most part horizontal. There are no metamorphic rocks showing themselves at the surface nearer than Little Rock, on the south side of the Arkansas River. Innumerable veins of milky quartz are seen traversing the sandstones and shales.

About seventeen years ago lead-ore was discovered at these mines by Mr. Kellogg; companies were organized and mining operations carried on extensively for about one year, when the flattering accounts of the gold discoveries in California caused the miners to leave, and the work, which had been badly conducted, was abandoned. Many tons of the ore, which is an argentiferous galena (containing sixty to two hundred ounces of silver to the ton), were extracted from the mine, and finally the greater part was shipped to England and sold at a good price. A smelting furnace has been erected on the grounds, but for lack of skill the proprietor never succeeded in working the ore profitably; consequently the impression was produced

« PreviousContinue »