The observations of Rose, however, on the Oreenstone of the Urslian Mountains, tend to prove the existence of that connection between the forms of Augite and hornblende which is essential to their constituting one genus, in a more satisfactory manner than any remark hitherto made. Ho discovered in a soft grayish Greenstone, near the village of Mostowaja, which is situated north of Katharinen burg, and on the road to Newiansk, and also at the gold-washings of Cavellinski, near Miask, in a Greenstone somewhat harder and darker than the former, imbedded crystals, having the form of A ugite, but not its cleavage planes, these last being found to coincide with those of Hornblende. This mineral was therefore either hornblende in the form of Augite, or Augite with the cleavage planes of hornblende.
At the village of lifuldakajewsk, near Miask, lie discovered still more interesting crystals embedded in a Greenstone similar to that last described. They were abundant, and possessed the form of A ugite : the smaller crystals had cleavage-planes parallel to the sides of the prism of Hornblende, and were similar in their appearance nod colour to those obtained from Cavellinski. The larger crystals, however, possessed a kernel of a grass-green colour, end of a lighter tint and greater lustre than the exterior. This kernel differed from the darker exterior portion of the the latter giving the cleavage of hornblende, while the former presented those of A vac, with faces sufficiently bright and perfeefsto admit of measurement by the reflect ing goniometer.
The observations of Mitscherlieh and Berthier on the formation of Augite as an artificial, product, are no interesting in themselves and throw so much light on the nature of A ugite in general, and on thou crystals we have just described, for which Rome proposes the name of Ural ite, that we cannot omit to notice them In this place. 2?Iitscher lieh has observed that at many foundries in Sweden and Germany the scoria NM/2MM the form, structu re, and chemical composition of co rta ir minerals found in nature. From tide source he has obtained epsverdt of forty varieties ; and among these specimens possessing the fora and structure of A ugite are frequently found, whereas //ornbissle has never been discovered. Guided by these observations, a mixture of silica, lime, and magnesia, in the proportion indicated by the formula of Diopside, given below, was submitted to fusion in the porcelain-ovens of Sevres, near Paris. On examination, the mass was found to have been completely fused: it possessed cleavage-planes corresponding with those of A +vile, and a hollow formed in the centre from the con traction in cooling contained crystals of the form of fig. 1. By these
processes they failed in obtaining crystals either of the form or struc ture of Hornblende.
Professor G. Rose, in accounting for this production of to the exclusion of hornblende, was led to consider that it was not the absence of the fluorine, or any error in the proportion of the elements, which prevented the production of Hornblende, but that it was the effect of the rapid cooling. This he fully confirmed by the following experiments :—A light-green variety of hornblende, the Straldstein of the Germans, from Zillerthal in the Tyrol, was submitted in a plati num crucible to the heat of a porcelain oven. It was completely fused, and in cooling had formed fibrous tufts of dark crystals, which however admitted of measurement by Wollaston'a goniometer, when the angles were found to correspond with those of Augite. A specimen of Dioptide, of the mine locality, was also fused ; it cooled into a dark mass, but regained its former structure.
We may therefore consider it to be demonstrated that A ugite is formed whenever the process of cooling, and consequently of crystal lisation, is rapid; and hornblende, when it is conducted more slowly. Many circumstances confirm this view : the L'ralites of Rose appear to be its natural consequence ; for as by the laws of caloric we know that the quantity of heat lost during equal portions of time varies with the temperature, the exterior portions of the crystal from this cause alone must have crystallised under a more gradual loss of heat than the interior, while at the same time the temperature would be maintained by the specific heat given out by the parts first consolidated. The general localities of A ugite and hornblende, and the minerals with which they are found associated, afford another argument in favour of this supposition; for hornblende is usually met with in Syenite, Trachyte, and Lava, accompanied by Quartz, Felspar, Albite, &c.,— minerals which decidedly require a slow process of cooling for their formation ; ou the contrary, A ugite occurs in Basalt and Lava with °Urine, which Mitacherlielt has recognised in the seorite of various foundries, and which is therefore formed by a process of rapid cooling. We are thus able to account for II. von Buch's remark in his observa tions on volcanoes, that those Lavas which contain Felspar have hornblende, but no A 'agile.