14. PHYLLITE.

I have given this name to a mineral which I received about a year ago from Mr. Nuttall, from Sterling, in Massachusetts. The color of one portion composed of flat micaceous scales, is brownish-black; but the greatest part consists of thin bent plates, having a bluish-gray color, and no bad resemblance to plumbago in its appearance.

The lustre is shining and resinous, or rather semi-metallic. Feel greasy.

The flat brown plates are so hard as not to be scratched by the knife, and not easily by quartz. But the plumbago-looking portion (which constitutes almost the whole specimen) is so soft, that it may be scratched by the nail of the finger. Sectile.

Specific gravity 2.889.

The constituents of the plumbago-looking portion of this mineral, were found to be,

Were we to suppose the silicates of potash and magnesia to be extraneous, the mineral would be a compound of,

3 atoms silicate of alumina,

1 atom silicate of peroxide of iron.

But as it is not crystalized, we have no means at present of determining what are its essential constituents. It will probably constitute a new species, being very different in its appearance from any mineral which I have hitherto had an opportunity of seeing. The brownish-black plates in some of their characters, approach pinite; but the composition and characters of the plumbago-looking portion, are very different from all the other species of stony minerals that I have

seen.

Note. Mr. Nuttall, with whom I have conferred respecting the minerals which he sent to Dr. Thomson, is not altogether certain that he recognises the substance called "phyllite." The specimen examined in this analysis, was labelled in his catalogue "titaniferous iron ;" and he informs me, that the ore was imbedded in what he considered as a singular ferruginous mica-slate. It is the latter substance which was analyzed. The brownish-black micaceous scales noticed by Dr. Thomson, are what Mr. Nuttall supposed to be an ore of iron.

15. HYDROUS SILICATE OF MAGNESIA.

There seems no reason to doubt that the Swedish mineral described in 1813, by Haussmann, under the name of picrolite, is the same with the precious serpentine of Werner. The external characters, as far as they have been given, are very nearly the same; and if we compare the analyses of these minerals by Hisinger, Stromeyer and Almroth, we shall find that they agree very closely, as may be seen by the following table.

The mineral which I am going to describe, is obviously a specimen of precious serpentine. I got it from Mr. Nuttall, among a collection of North American minerals. It was found at Easton, in Pennsylvania.

The color was yellow, with a slight shade of green. It appeared when examined by a microscope, to be composed of a congeries of semi-transparent grains.

It was easily scratched by a knife, but not by fluor-spar. Its specific gravity was at first 2·53; but after digestion in muriatic acid, to remove some calcareous spar with which it was contaminated, the specific gravity was reduced to 3.39. The constituents were found to be,

Perhaps it may be considered as a compound of 5 atoms bisilicate of magnesia, and 3 atoms bihydrate of magnesia. The symbol would be 5 MnS2 + 6 MnAq. This view would accord with the constituents found, were we to consider the iron as an accidental ingredient.

16. BISILICATE OF MAGNESIA.

The mineral, which from its composition I distinguish by the name of bisilicate of magnesia, was sent me from Bolton, Massachusetts, by Mr. Nuttall. It bears so much resemblance to the picrosmine of Haidinger, both in its character and composition, that I strongly suspect the two minerals will turn out mere varieties.

The bisilicate of magnesia has a white colour, with a slight shade of green. Its powder is white.

It consists of a congeries of prismatic crystals very irregularly disposed, and so involved in each other, that the shape cannot be distinctly made out. The few faces which were tolerably distinct, lead to the notion that the crystals are four-sided oblique prisms.

Lustre glassy. Translucent on the edges.

The crystals cleave longitudinally, but in no other direction.

Scratched by the knife, but not easily.

Specific gravity 2.976.

The constituents of this mineral are,

If the alumina and protoxide of iron be only accidental substances, then the constituents of the mineral are,

The chief difference between the mineral described by Haidinger from Bohemia, and the American mineral, consists in the former containing 7.301 of water, while the latter is anhydrous. The specific gravity of Haidinger's mineral (owing to the water) is only 2·66, while that of the American mineral is 2.976. I have little doubt that they will be found ultimately, to be only varieties of the same species.

17. HYPERSTHENE.

The three mineral species, pyroxene, amphibole, and hypersthene, have considerable analogy both in their situation and composition. They all occur as constituents of trap rocks,