180 M. C. Deville on tlie origin of Granite. 



fusion. But it is scarcely necessary to dwell upon the absolute 

 difference of physical conditions between a few grammes of this 

 quartz fused and immediately cooled, and masses of the substance 

 imbedded in a granite block. If it be objected that in no case 

 in nature, not even in granitic veins of small dimensions, which 

 therefore are in conditions most resembling those of the labora- 

 tory, has quartz been found in a vitreous condition, it might be 

 answered that we are entirely ignorant of the limits to the sta- 

 bility of quartz in this condition. If, as I think, the vitreous 

 state is an abnormal condition for all bodies capable of acquiring 

 it* — a state in which the molecules are retained at too great 

 distances from each other by an excess of latent heat, — each of 

 them ought to tend to still further removal, in order to obtain 

 position of stable equilibrium, which is in fact the crystalline 

 state. This is well seen in sulphur, arsenious acid, &c. I have 

 shown that soft sulphur left to itself, although gradually ap- 

 proaching octahedral sulphur nearer and nearer, had not become 

 changed into that state even after several years : this was per- 

 ceptible from the differences of density. But inasmuch as there 

 are necessary limits to the operation, we see that by prolonging 

 the experiment as long as we like, we could never affirm that the 

 change was complete. Can it not be conceived that the quartz 

 of granite (originally vitreous like sulphur, like vitreous arse- 

 nious acid, like ordinary glass) has undergone, after a long time 

 and under favourable conditions, a molecular change which has 

 altered it into the crystalline state without imparting to it any 

 external geometrical form ? 



The beautiful experiments in which M. de Senarmont and 

 M. Daubree have produced quartz in small but perfect crystals 

 or in concretionary masses, are well fitted to explain the origin 

 of quartz in veins, in geodes, and even in stanniferous masses ; 

 in short, to use an idea of the first importance introduced into 

 science by M. Elie de Beaumont f, they explain the presence of 

 quartz in all cases in which it is connected with the phenomena 



* I have shown (Comptes Rendus, vol. xl. p. 769) that the properties of 

 superfusibility by temper are far from belonging to all bodies. The metals 

 which I have examined (lead, zinc, and bismuth) have not exhibited it ; 

 nor has chloride of sodium. It is remarkable that alumina, a body re- 

 sembling silica in many respects, is entirely free from it. While quartz 

 presented the greatest difference in density between the crystallized and 

 the vitreous state, fused and tempered corundum had exactly the same 

 density as natural corundum. 



t Note on Volcanic and Metalliferous Emanations " (Bulletin de la 

 Socie'te' Giologique de France, 2 seV. vol. iv. p. 1250). M. Bernhard Cotta, 

 in giving a complete translation of this memoir (Gangstudien, 4th part, 

 1850), has performed a real service for those persons on the other side of 

 the Rhine who are interested in these questions. 



