The difficulty of devising a natural classification of minerals has been recognized by most mineralogical writers, and up to the present time no very satisfactory arrangement has been generally adopted. In the classification of the animal and vegetable kingdoms, although the systems have greatly varied from time to time, something like uniformity has pretty generally existed ever since Linnaeus proposed his famous system of double nomenclature ; but in mineralogy every writer does that which is right in his own eyes—not because there is no king—but because they are many and mutually antagonistic.

Rather more than twelve months ago Sir D. Jephson Norreys, Bart., of Mallow Castle, county Cork, directed my attention to a beautiful mineral which had been obtained by a friend and neighbour of his, Miss Cotter, of Rockforest. Through his kindness I was enabled to see the circumstances under which the mineral occurred ; and also to obtain from Rockforest some fine specimens thereof.

The mineral itself is specially characterised by the peculiarity of its lustre, which it possesses in a high degree, producing an aspect of a very unique character. Concerning the kind of lustre, this is somewhat difficult to define.

In the course of an examination of such Scottish garnets as were pure enough for analysis, I found that four had a composition which was very similar, but which differed from that of any known, and that to an extent entitling them to be regarded as constituting a well-marked variety.

These garnets, from their purity of colour and transparency, would all be classed as precious garnets–they are, indeed, the most brilliantly coloured which the northern portion of the kingdom affords.

In No. V. of this Magazine (page 149) there appeared a paper on "Some new Minerals in the Collection of the Hunterian Museum, Glasgow," in which I gave a description and analysis of a new Sulphide of Lead, Manganese, Iron, and Zinc, to which I gave the name of "Youngite." In a note to his abstract of the above paper for the Journal of the Chemical Society of January, 1878, Dr. Burghardt, expressed an opinion that the "Youngite" was only a mixture of Galena, Blende, Alabandite (Mn S), and Iron Pyrites; and consequently had no claim to be called a new mineral. Although my analyses agreed closely, and coincided with such a probable formula that there was little reason to doubt their accuracy, I am glad to be able to place the matter beyond dispute.

In a paper read before the Chemical Society I gave a detailed account of a curious reaction of Manganese salts, and showed that Manganese dioxide resembling pyrolusite could be obtained by the reaction. I have since made many samples, and have obtained nodules so like the natural mineral, that I thought that an account of the method might have some interest for mineralogists. When manganous nitrate is dissolved in strong nitric acid and warmed, and a few chips of potassic chlorate added, there is precipitated in the liquid black oxide of manganese in the form of flat plates which, when very thin, are of a beautiful purple, but when thicker are of a red colour. The whole of the manganese is precipitated in this form, but when the strength of the acid and the temperature are made to vary, the distribution of the plates may be changed.

This is a highly vitreous transparent reddish brown mineral, which occurs with quartz and rhodocrosite. Its H. is 3.5, and sp. gr. only 2.49.

When heated in a tube closed at one end it gives off water, but is otherwise unchanged. More strongly heated in platinum forceps it loses colour and very slightly fuses on the edges.

It is brittle, and has a highly conchoidal fracture. When digested with hydrochloric acid, oxide of manganese is dissolved out, and the silica which remains is perfectly colourless.

The following brief notes may be of some interest to students of Cornish Mineralogy.

1 st.—New Localities.

Scheelite.—This occurs as a partial replacement of Wolfram at East Pool Mine, where it was first noticed by Mr. Cornelius Beringer, of Redruth, an Associate Member of this Society. Hitherto it has only been found at Pengelly Croft, Huel Mandlin, and Levant Mine, in Cornwall, and at Huel Friendship, in Devon.

The number of planes is extremely variable in many crystals. Those of the same substance produced under modified conditions, even when issuing from the same solution, are occasionally very different in this respect. Generally the forms become less complicated and the number of planes diminishes, a certain number Of them definitely disappearing, during the crystal's increase in volume. Such transitory planes are very frequently defective in parallelism.

Two kinds of planes may be distinguished on crystals of any system ; some which are constant, others which may be termed variable; the latter being occasionally wanting, are in other cases very numerous.