Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/517

 Of these, A is by Damour ; it is of Harmotome, the opaque variety. B, by Rammelsberg, is probably of the same ; it is simply called Harmotome from Strontian by him. C is by Damour ; it is one of two analyses of Morvenite, by which he established the identity of Morvenite with Harmotome. D is Dr. Reynolds's analysis.

From this it appears that these crystals are a particularly pure form of the mineral, being nearly perfectly free from alkalies ; and they certainly deserve a name, to the full as much as Thomson's Morvenite does.

The only special interest which they possess is crystallographical. In all the crystals of Harmotome figured by either Dufrenoy or Dana the termination of the prisms is quadrifacial. Dufrenoy mentions that occasionally a very obtuse quadrangular pyramid is found, similar to that which sometimes occurs in Anatase ; and Descloiseaux, in his recent paper* on the crystallography of the species, has determined the angle between the opposite faces of this pyramid to be 178° 20'. Dana gives in his last edition such a pyramid.

I have not myself been able to measure the angle between the faces of the dihedral termination of the prisms which I now submit to the Society ; it is an extremely obtuse one ; and it seems probable that they will ultimately turn out either to be two of the four faces spoken of by Deseloiseaux, or else the faces of the brachydome cor- responding to that pyramid.

In conclusion I would only draw attention to the specimens which I have brought down, as evidence that the neighbourhood of Strontian is still almost as promising a field for the mineralogist as any in these islands.

Discussion.

Mr. W. W. Smyth mentioned the wonderful collection of minerals from Strontian which had been brought to the Great Exhibition of 1851, which gave a most striking idea of the mineral riches of the locality. The occurrence of such a series of different substances in one locality in the granite was almost unparalleled, though in the Andreasberg mines, in clay slate, they were to some extent rivalled. The features, however, differed in the two places, more silver and a greater number of zeolites being present in the Hartz mines.

Mr. D. Forbes observed that Harmotome occurred also at the Kongsberg silver-mines in Norway, at a distance from granite. He thought it remarkable that these crystals of peculiar form occurred in the same spot and in connexion with crystals of the same sub- stance but of the ordinary form.

Mr. Davis remarked that Celestine was also to be placed on the list of the minerals from Strontian. Harmotome had been found in the same form of double crystals at Bodenmais in Bavaria.

Mr. Scott stated, in reply to a question from the Chairman, that the mineral had not been as yet optically examined, but that if he could procure more of it he should be happy to place it at the dis-


 * Ann. des Mines, 4th ser. torn. ix. p. 339.